deploy: 48cb100473bb6fae52cb58d39192d50c08977463

index.html

@@ -17,7 +17,7 @@
 
 <h2 class='titleHead'>The Linux Kernel Module Programming Guide</h2>
 <div class='author'><span class='ecrm-1200'>Peter Jay Salzman, Michael Burian, Ori Pomerantz, Bob Mottram, Jim Huang</span></div><br />
-<div class='date'><span class='ecrm-1200'>August 16, 2021</span></div>
+<div class='date'><span class='ecrm-1200'>August 17, 2021</span></div>
                                                                   
 
                                                                   
@@ -280,7 +280,7 @@ module.
    <pre class='fancyvrb' id='fancyvrb10'><a id='x1-12008r1'></a><span class='ecrm-0500'>1</span><span id='textcolor3'><span class='ectt-0800'>/*</span></span> 
 <a id='x1-12010r2'></a><span class='ecrm-0500'>2</span><span id='textcolor4'><span class='ectt-0800'> * hello-1.c - The simplest kernel module.</span></span> 
 <a id='x1-12012r3'></a><span class='ecrm-0500'>3</span><span id='textcolor5'><span class='ectt-0800'> */</span></span> 
-<a id='x1-12014r4'></a><span class='ecrm-0500'>4</span><span id='textcolor6'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor7'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-12014r4'></a><span class='ecrm-0500'>4</span><span id='textcolor6'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor7'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-12016r5'></a><span class='ecrm-0500'>5</span><span id='textcolor8'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor9'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-12018r6'></a><span class='ecrm-0500'>6</span> 
 <a id='x1-12020r7'></a><span class='ecrm-0500'>7</span><span id='textcolor10'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> init_module(</span><span id='textcolor11'><span class='ectt-0800'>void</span></span><span class='ectt-0800'>)</span> 
@@ -425,7 +425,7 @@ technique:
 <a id='x1-13010r3'></a><span class='ecrm-0500'>3</span><span id='textcolor30'><span class='ectt-0800'> * This is preferred over using init_module() and cleanup_module().</span></span> 
 <a id='x1-13012r4'></a><span class='ecrm-0500'>4</span><span id='textcolor31'><span class='ectt-0800'> */</span></span> 
 <a id='x1-13014r5'></a><span class='ecrm-0500'>5</span><span id='textcolor32'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor33'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-13016r6'></a><span class='ecrm-0500'>6</span><span id='textcolor34'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor35'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-13016r6'></a><span class='ecrm-0500'>6</span><span id='textcolor34'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor35'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-13018r7'></a><span class='ecrm-0500'>7</span><span id='textcolor36'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor37'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-13020r8'></a><span class='ecrm-0500'>8</span> 
 <a id='x1-13022r9'></a><span class='ecrm-0500'>9</span><span id='textcolor38'><span class='ectt-0800'>static</span></span><span class='ectt-0800'> </span><span id='textcolor39'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> __init hello_2_init(</span><span id='textcolor40'><span class='ectt-0800'>void</span></span><span class='ectt-0800'>)</span> 
@@ -462,7 +462,7 @@ is as simple as this:
 see, some things get hardwired into the kernel (<span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-y</span></span></span>) but where are all those <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-m</span></span></span>
 gone? Those familiar with shell scripts will easily be able to spot them. For those not,
 the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-$(CONFIG_FOO)</span></span></span> entries you see everywhere expand into <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-y</span></span></span> or <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-m</span></span></span>,
-depending on whether the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>CONFIG_FOO</span></span></span> variable has been set to y or m. While we are
+depending on whether the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>CONFIG_FOO</span></span></span> variable has been set to <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>y</span></span></span> or <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>m</span></span></span>. While we are
 at it, those were exactly the kind of variables that you have set in the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>.config</span></span></span> file in
 the top-level directory of Linux kernel source tree, the last time when you said
 <code> <span class='ectt-1000'>make menuconfig</span>
@@ -494,7 +494,7 @@ memory: 236k freed, this is precisely what the kernel is freeing.
 <a id='x1-14009r2'></a><span class='ecrm-0500'>2</span><span id='textcolor57'><span class='ectt-0800'> * hello-3.c - Illustrating the __init, __initdata and __exit macros.</span></span> 
 <a id='x1-14011r3'></a><span class='ecrm-0500'>3</span><span id='textcolor58'><span class='ectt-0800'> */</span></span> 
 <a id='x1-14013r4'></a><span class='ecrm-0500'>4</span><span id='textcolor59'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor60'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-14015r5'></a><span class='ecrm-0500'>5</span><span id='textcolor61'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor62'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-14015r5'></a><span class='ecrm-0500'>5</span><span id='textcolor61'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor62'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-14017r6'></a><span class='ecrm-0500'>6</span><span id='textcolor63'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor64'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-14019r7'></a><span class='ecrm-0500'>7</span> 
 <a id='x1-14021r8'></a><span class='ecrm-0500'>8</span><span id='textcolor65'><span class='ectt-0800'>static</span></span><span class='ectt-0800'> </span><span id='textcolor66'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> hello3_data __initdata = 3;</span> 
@@ -543,7 +543,7 @@ example.
 <a id='x1-15005r2'></a><span class='ecrm-0500'>2</span><span id='textcolor82'><span class='ectt-0800'> * hello-4.c - Demonstrates module documentation.</span></span> 
 <a id='x1-15007r3'></a><span class='ecrm-0500'>3</span><span id='textcolor83'><span class='ectt-0800'> */</span></span> 
 <a id='x1-15009r4'></a><span class='ecrm-0500'>4</span><span id='textcolor84'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor85'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-15011r5'></a><span class='ecrm-0500'>5</span><span id='textcolor86'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor87'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-15011r5'></a><span class='ecrm-0500'>5</span><span id='textcolor86'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor87'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-15013r6'></a><span class='ecrm-0500'>6</span><span id='textcolor88'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor89'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-15015r7'></a><span class='ecrm-0500'>7</span> 
 <a id='x1-15017r8'></a><span class='ecrm-0500'>8</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor90'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
@@ -800,7 +800,7 @@ error as follows:
 insmod: error inserting 'poet_atkm.ko': -1 Invalid module format
 </pre>
 <!-- l. 489 --><p class='nopar'>
-</p><!-- l. 491 --><p class='indent'>   Less cryptical information are logged to the systemd journal:
+</p><!-- l. 491 --><p class='indent'>   Less cryptic information is logged to the systemd journal:
                                                                   
 
                                                                   
@@ -833,8 +833,8 @@ name:           hello_4
 vermagic:       5.4.0-70-generic SMP mod_unload modversions
 </pre>
 <!-- l. 513 --><p class='nopar'>
-</p><!-- l. 515 --><p class='indent'>   To overcome this problem we could resort to the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>--force-vermagic</span></span></span>
+</p><!-- l. 515 --><p class='indent'>   To overcome this problem we could resort to the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>--force-vermagic</span></span></span> option,
-option, but this solution is potentially unsafe, and unquestionably inacceptable
+but this solution is potentially unsafe, and unquestionably unacceptable
 in production modules. Consequently, we want to compile our module in
 an environment which was identical to the one in which our precompiled
 kernel was built. How to do this, is the subject of the remainder of this
@@ -847,11 +847,11 @@ tree: <code>  <span class='ectt-1000'>cp /boot/config-</span><span id='textcolo
 </code>.
 </p><!-- l. 524 --><p class='indent'>   Let’s focus again on the previous error message: a closer look at the version magic
 strings suggests that, even with two configuration files which are exactly the same, a
-slight difference in the version magic could be possible, and it is sufficient to
+slight difference in the version magic could be possible, and it is sufficient to prevent
-prevent insertion of the module into the kernel. That slight difference, namely
+insertion of the module into the kernel. That slight difference, namely the
-the custom string which appears in the module’s version magic and not in
+custom string which appears in the module’s version magic and not in the
-the kernel’s one, is due to a modification with respect to the original, in
+kernel’s one, is due to a modification with respect to the original, in the
-the makefile that some distribution include. Then, examine your <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>Makefile</span></span></span>,
+makefile that some distributions include. Then, examine your <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>Makefile</span></span></span>,
 and make sure that the specified version information matches exactly the
 one used for your current kernel. For example, you makefile could start as
 follows:
@@ -974,7 +974,7 @@ data into strings and write the string data using the low-level system call
 <a id='x1-21026r6'></a><span class='ecrm-0500'>6</span><span class='ectt-0800'>    </span><span id='textcolor262'><span class='ectt-0800'>return</span></span><span class='ectt-0800'> 0;</span> 
 <a id='x1-21028r7'></a><span class='ecrm-0500'>7</span><span class='ectt-0800'>}</span></pre>
 <!-- l. 608 --><p class='indent'>   with <code>  <span class='ectt-1000'>gcc -Wall -o hello hello.c</span>
-</code>. Run the exectable with <code>  <span class='ectt-1000'>strace ./hello</span>
+</code>. Run the executable with <code>  <span class='ectt-1000'>strace ./hello</span>
 </code>. Are you impressed? Every line you see corresponds to a system call. <a href='https://strace.io/'>strace</a> is a
 handy program that gives you details about what system calls a program is
 making, including which call is made, what its arguments are and what it
@@ -1036,8 +1036,8 @@ symbols.
 entire kernel, so this is definitely an issue. The best way to deal with this is to declare
 all your variables as static and to use a well-defined prefix for your symbols. By
 convention, all kernel prefixes are lowercase. If you do not want to declare everything
-as static, another option is to declare a symbol table and register it with a kernel. We
+as static, another option is to declare a symbol table and register it with the kernel.
-will get to this later.
+We will get to this later.
 </p><!-- l. 652 --><p class='indent'>   The file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/kallsyms</span></span></span> holds all the symbols that the kernel knows about and
 which are therefore accessible to your modules since they share the kernel’s
 codespace.
@@ -1583,7 +1583,7 @@ conditional compilation directives. The way to do this to compare the macro
 information to processes — the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> file system. Originally designed to allow easy
 access to information about processes (hence the name), it is now used by every bit
 of the kernel which has something interesting to report, such as <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/modules</span></span></span>
-which provides the list of modules and <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/meminfo</span></span></span> which stats memory usage
+which provides the list of modules and <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/meminfo</span></span></span> which gathers memory usage
 statistics.
 </p><!-- l. 943 --><p class='indent'>   The method to use the proc file system is very similar to the one used with device
 drivers — a structure is created with all the information needed for the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> file,
@@ -1620,7 +1620,7 @@ function <code>  <span class='ectt-1000'>procfile_read</span>
 </code>. The return value is a <code>  <span id='textcolor548'><span class='ectt-1000'>struct</span></span><span class='ectt-1000'> proc_dir_entry</span>
 </code>, and it will be used to configure the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> (for example, the owner
 of this file). A null return value means that the creation has failed.
-</p><!-- l. 959 --><p class='indent'>   Each time, everytime the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> is read, the function
+</p><!-- l. 959 --><p class='indent'>   Every time the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> is read, the function
 <code> <span class='ectt-1000'>procfile_read</span>
 </code> is called. Two parameters of this function are very important: the buffer
 (the second parameter) and the offset (the fourth one). The content of the
@@ -2200,7 +2200,7 @@ the same way as in the previous example.
 <!-- l. 1076 --><p class='indent'>   If you want more information, you can read this web page:
 </p>
      <ul class='itemize1'>
-     <li class='itemize'><a class='url' href='http://lwn.net/Articles/22355/'><span class='ectt-1000'>http://lwn.net/Articles/22355/</span></a>
+     <li class='itemize'><a class='url' href='https://lwn.net/Articles/22355/'><span class='ectt-1000'>https://lwn.net/Articles/22355/</span></a>
      </li>
      <li class='itemize'><a class='url' href='https://kernelnewbies.org/Documents/SeqFileHowTo'><span class='ectt-1000'>https://kernelnewbies.org/Documents/SeqFileHowTo</span></a></li></ul>
 <!-- l. 1083 --><p class='indent'>   You can also read the code of <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/fs/seq_file.c'>fs/seq_file.c</a> in the linux kernel.
@@ -2327,7 +2327,7 @@ device file to write things to the modem (either modem commands or data to
 be sent through the phone line) and read things from the modem (either
 responses for commands or the data received through the phone line). However,
 this leaves open the question of what to do when you need to talk to the
-serial port itself, for example to send the rate at which data is sent and
+serial port itself, for example to configure the rate at which data is sent and
 received.
                                                                   
 
@@ -2360,7 +2360,7 @@ ioctl.c.
 </p><!-- l. 1155 --><p class='indent'>   If you want to use ioctls in your own kernel modules, it is best to receive an
 official ioctl assignment, so if you accidentally get somebody else’s ioctls, or if they
 get yours, you’ll know something is wrong. For more information, consult the kernel
-source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/driver-api/ioctl.rst'>Documentation/driver-api/ioctl.rst</a>.
+source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/userspace-api/ioctl/ioctl-number.rst'>Documentation/userspace-api/ioctl/ioctl-number.rst</a>.
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb49'><a id='x1-39009r1'></a><span class='ecrm-0500'>1</span><span id='textcolor964'><span class='ectt-0800'>/*</span></span> 
@@ -2843,30 +2843,30 @@ source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/l
 <a id='x1-39951r196'></a><span class='ecrm-0500'>196</span> 
 <a id='x1-39953r197'></a><span class='ecrm-0500'>197</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1336'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-39955r198'></a><span class='ecrm-0500'>198</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1337'><span class='ectt-0800'>"This is test_ioctl module"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1165 --><p class='noindent'>
+<!-- l. 1164 --><p class='noindent'>
 </p>
                                                                   
 
                                                                   
    <h3 class='sectionHead' id='system-calls'><span class='titlemark'>0.10   </span> <a id='x1-400000.10'></a>System Calls</h3>
-<!-- l. 1167 --><p class='noindent'>So far, the only thing we’ve done was to use well defined kernel mechanisms to
+<!-- l. 1166 --><p class='noindent'>So far, the only thing we’ve done was to use well defined kernel mechanisms to
 register <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files and device handlers. This is fine if you want to do something the
 kernel programmers thought you’d want, such as write a device driver. But what if
 you want to do something unusual, to change the behavior of the system in some
 way? Then, you are mostly on your own.
-</p><!-- l. 1172 --><p class='indent'>   If you are not being sensible and using a virtual machine then this is where kernel
+</p><!-- l. 1171 --><p class='indent'>   If you are not being sensible and using a virtual machine then this is where kernel
 programming can become hazardous. While writing the example below, I killed the
 <code> <span class='ectt-1000'>open()</span>
 </code> system call. This meant I could not open any files, I could not run any
 programs, and I could not shutdown the system. I had to restart the virtual
-machine. No important files got anihilated, but if I was doing this on some live
+machine. No important files got annihilated, but if I was doing this on some live
 mission critical system then that could have been a possible outcome. To
 ensure you do not lose any files, even within a test environment, please run
 <code> <span class='ectt-1000'>sync</span>
 </code> right before you do the <code>  <span class='ectt-1000'>insmod</span>
 </code> and the <code>  <span class='ectt-1000'>rmmod</span>
 </code>.
-</p><!-- l. 1179 --><p class='indent'>   Forget about <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files, forget about device files. They are just minor details.
+</p><!-- l. 1178 --><p class='indent'>   Forget about <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files, forget about device files. They are just minor details.
 Minutiae in the vast expanse of the universe. The real process to kernel
 communication mechanism, the one used by all processes, is <span class='ecti-1000'>system calls</span>. When a
 process requests a service from the kernel (such as opening a file, forking to a new
@@ -2875,11 +2875,11 @@ change the behaviour of the kernel in interesting ways, this is the place to do
 it. By the way, if you want to see which system calls a program uses, run
 <code> <span class='ectt-1000'>strace &lt;arguments&gt;</span>
 </code>.
-</p><!-- l. 1187 --><p class='indent'>   In general, a process is not supposed to be able to access the kernel. It can not
+</p><!-- l. 1186 --><p class='indent'>   In general, a process is not supposed to be able to access the kernel. It can not
 access kernel memory and it can’t call kernel functions. The hardware of the CPU
 enforces this (that is the reason why it is called “protected mode” or “page
 protection”).
-</p><!-- l. 1191 --><p class='indent'>   System calls are an exception to this general rule. What happens is that the
+</p><!-- l. 1190 --><p class='indent'>   System calls are an exception to this general rule. What happens is that the
 process fills the registers with the appropriate values and then calls a special
 instruction which jumps to a previously defined location in the kernel (of course, that
 location is readable by user processes, it is not writable by them). Under Intel CPUs,
@@ -2887,7 +2887,7 @@ this is done by means of interrupt 0x80. The hardware knows that once you jump t
 this location, you are no longer running in restricted user mode, but as the
 operating system kernel — and therefore you’re allowed to do whatever you
 want.
-</p><!-- l. 1196 --><p class='indent'>   The location in the kernel a process can jump to is called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>system_call</span></span></span>. The
+</p><!-- l. 1195 --><p class='indent'>   The location in the kernel a process can jump to is called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>system_call</span></span></span>. The
 procedure at that location checks the system call number, which tells the kernel what
 service the process requested. Then, it looks at the table of system calls
 (<code>  <span class='ectt-1000'>sys_call_table</span>
@@ -2900,7 +2900,7 @@ different process, if the process time ran out). If you want to read this code,
 at the source file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>arch/$(architecture)/kernel/entry.S</span></span></span>, after the line
 <code> <span class='ectt-1000'>ENTRY(system_call)</span>
 </code>.
-</p><!-- l. 1202 --><p class='indent'>   So, if we want to change the way a certain system call works, what we need to do
+</p><!-- l. 1201 --><p class='indent'>   So, if we want to change the way a certain system call works, what we need to do
 is to write our own function to implement it (usually by adding a bit of our own
 code, and then calling the original function) and then change the pointer at
 <code> <span class='ectt-1000'>sys_call_table</span>
@@ -2908,7 +2908,7 @@ code, and then calling the original function) and then change the pointer at
 don’t want to leave the system in an unstable state, it’s important for
 <code> <span class='ectt-1000'>cleanup_module</span>
 </code> to restore the table to its original state.
-</p><!-- l. 1205 --><p class='indent'>   The source code here is an example of such a kernel module. We want to “spy” on a certain
+</p><!-- l. 1204 --><p class='indent'>   The source code here is an example of such a kernel module. We want to “spy” on a certain
 user, and to <code>  <span class='ectt-1000'>pr_info()</span>
 </code> a message whenever that user opens a file. Towards this end, we
 replace the system call to open a file with our own function, called
@@ -2918,7 +2918,7 @@ spy on, it calls <code>  <span class='ectt-1000'>pr_info()</span>
 </code> to display the name of the file to be opened. Then, either way, it calls the original
 <code> <span class='ectt-1000'>open()</span>
 </code> function with the same parameters, to actually open the file.
-</p><!-- l. 1211 --><p class='indent'>   The <code>  <span class='ectt-1000'>init_module</span>
+</p><!-- l. 1210 --><p class='indent'>   The <code>  <span class='ectt-1000'>init_module</span>
 </code> function replaces the appropriate location in
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> and keeps the original pointer in a variable. The
@@ -2936,7 +2936,7 @@ with <code>  <span class='ectt-1000'>B_open</span>
 </code>, which will call what it thinks is the original system call,
 <code> <span class='ectt-1000'>A_open</span>
 </code>, when it’s done.
-</p><!-- l. 1218 --><p class='indent'>   Now, if B is removed first, everything will be well — it will simply restore the system
+</p><!-- l. 1217 --><p class='indent'>   Now, if B is removed first, everything will be well — it will simply restore the system
 call to <code>  <span class='ectt-1000'>A_open</span>
 </code>, which calls the original. However, if A is removed and then B is removed, the
 system will crash. A’s removal will restore the system call to the original,
@@ -2959,7 +2959,7 @@ problem. When A is removed, it sees that the system call was changed to
 </code> will still try to call <code>  <span class='ectt-1000'>A_open</span>
 </code> which is no longer there, so that even without removing B the system would
 crash.
-</p><!-- l. 1226 --><p class='indent'>   Note that all the related problems make syscall stealing unfeasiable for
+</p><!-- l. 1225 --><p class='indent'>   Note that all the related problems make syscall stealing unfeasible for
 production use. In order to keep people from doing potential harmful things
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> is no longer exported. This means, if you want to do something more than a mere
@@ -2967,8 +2967,8 @@ dry run of this example, you will have to patch your current kernel in order to
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> exported. In the example directory you will find a README and the patch. As you
 can imagine, such modifications are not to be taken lightly. Do not try this on
-valueable systems (ie systems that you do not own - or cannot restore easily). You
+valuable systems (ie systems that you do not own - or cannot restore easily). You will
-will need to get the complete sourcecode of this guide as a tarball in order to get the
+need to get the complete sourcecode of this guide as a tarball in order to get the
 patch and the README. Depending on your kernel version, you might even need to
 hand apply the patch.
 </p><!-- l. 1 --><p class='indent'>
@@ -3110,13 +3110,13 @@ hand apply the patch.
 <a id='x1-40302r135'></a><span class='ecrm-0500'>135</span><span class='ectt-0800'>module_exit(syscall_end);</span> 
 <a id='x1-40304r136'></a><span class='ecrm-0500'>136</span> 
 <a id='x1-40306r137'></a><span class='ecrm-0500'>137</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1471'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1237 --><p class='noindent'>
+<!-- l. 1236 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='blocking-processes-and-threads'><span class='titlemark'>0.11   </span> <a id='x1-410000.11'></a>Blocking Processes and threads</h3>
-<!-- l. 1239 --><p class='noindent'>
+<!-- l. 1238 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='sleep'><span class='titlemark'>0.11.1   </span> <a id='x1-420000.11.1'></a>Sleep</h4>
-<!-- l. 1241 --><p class='noindent'>What do you do when somebody asks you for something you can not do right
+<!-- l. 1240 --><p class='noindent'>What do you do when somebody asks you for something you can not do right
 away? If you are a human being and you are bothered by a human being, the
 only thing you can say is: "<span class='ecti-1000'>Not right now, I’m busy. Go away!</span>". But if you
 are a kernel module and you are bothered by a process, you have another
@@ -3127,21 +3127,21 @@ processes are being put to sleep by the kernel and woken up all the time (that
                                                                   
 is the way multiple processes appear to run on the same time on a single
 CPU).
-</p><!-- l. 1247 --><p class='indent'>   This kernel module is an example of this. The file (called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/sleep</span></span></span>) can only
+</p><!-- l. 1246 --><p class='indent'>   This kernel module is an example of this. The file (called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/sleep</span></span></span>) can only
 be opened by a single process at a time. If the file is already open, the kernel module
 calls <code>  <span class='ectt-1000'>wait_event_interruptible</span>
 </code>. The easiest way to keep a file open is to open it with:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb53'><a id='x1-42004r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>tail -f</span></pre>
-<!-- l. 1256 --><p class='indent'>   This function changes the status of the task (a task is the kernel data structure
+<!-- l. 1255 --><p class='indent'>   This function changes the status of the task (a task is the kernel data structure
 which holds information about a process and the system call it is in, if any) to
 <code> <span class='ectt-1000'>TASK_INTERRUPTIBLE</span>
 </code>, which means that the task will not run until it is woken up somehow, and adds it to
 WaitQ, the queue of tasks waiting to access the file. Then, the function calls the
 scheduler to context switch to a different process, one which has some use for the
 CPU.
-</p><!-- l. 1260 --><p class='indent'>   When a process is done with the file, it closes it, and
+</p><!-- l. 1259 --><p class='indent'>   When a process is done with the file, it closes it, and
 <code> <span class='ectt-1000'>module_close</span>
 </code> is called. That function wakes up all the processes in the queue (there’s no
 mechanism to only wake up one of them). It then returns and the process which just
@@ -3151,20 +3151,20 @@ Eventually, one of the processes which was in the queue will be given control
 of the CPU by the scheduler. It starts at the point right after the call to
 <code> <span class='ectt-1000'>module_interruptible_sleep_on</span>
 </code>.
-</p><!-- l. 1267 --><p class='indent'>   This means that the process is still in kernel mode - as far as the process
+</p><!-- l. 1266 --><p class='indent'>   This means that the process is still in kernel mode - as far as the process
 is concerned, it issued the open system call and the system call has not
 returned yet. The process does not know somebody else used the CPU for
 most of the time between the moment it issued the call and the moment it
 returned.
-</p><!-- l. 1270 --><p class='indent'>   It can then proceed to set a global variable to tell all the other processes that the
+</p><!-- l. 1269 --><p class='indent'>   It can then proceed to set a global variable to tell all the other processes that the
 file is still open and go on with its life. When the other processes get a piece of the
 CPU, they’ll see that global variable and go back to sleep.
-</p><!-- l. 1273 --><p class='indent'>   So we will use <code>  <span class='ectt-1000'>tail -f</span>
+</p><!-- l. 1272 --><p class='indent'>   So we will use <code>  <span class='ectt-1000'>tail -f</span>
 </code> to keep the file open in the background, while trying to access it with another
 process (again in the background, so that we need not switch to a different vt). As
 soon as the first background process is killed with kill %1 , the second is woken up, is
 able to access the file and finally terminates.
-</p><!-- l. 1276 --><p class='indent'>   To make our life more interesting, <code>  <span class='ectt-1000'>module_close</span>
+</p><!-- l. 1275 --><p class='indent'>   To make our life more interesting, <code>  <span class='ectt-1000'>module_close</span>
 </code> does not have a monopoly on waking up the processes which wait to access the file.
 A signal, such as <span class='ecti-1000'>Ctrl +c </span>(<span class='ecbx-1000'>SIGINT</span>) can also wake up a process. This is because we
 used <code>  <span class='ectt-1000'>module_interruptible_sleep_on</span>
@@ -3174,11 +3174,11 @@ used <code>  <span class='ectt-1000'>module_interruptible_sleep_on</span>
                                                                   
 </code> instead, but that would have resulted in extremely angry users whose <span class='ecti-1000'>Ctrl+c</span>’s are
 ignored.
-</p><!-- l. 1280 --><p class='indent'>   In that case, we want to return with
+</p><!-- l. 1279 --><p class='indent'>   In that case, we want to return with
 <code> <span class='ectt-1000'>-EINTR</span>
 </code> immediately. This is important so users can, for example, kill the process before it
 receives the file.
-</p><!-- l. 1282 --><p class='indent'>   There is one more point to remember. Some times processes don’t want to sleep, they want
+</p><!-- l. 1281 --><p class='indent'>   There is one more point to remember. Some times processes don’t want to sleep, they want
 either to get what they want immediately, or to be told it cannot be done. Such processes
 use the <code>  <span class='ectt-1000'>O_NONBLOCK</span>
 </code> flag when opening the file. The kernel is supposed to respond by returning with the error
@@ -3214,7 +3214,7 @@ $ cat_nonblock /proc/sleep
 Last input:
 $
 </pre>
-<!-- l. 1307 --><p class='nopar'>
+<!-- l. 1306 --><p class='nopar'>
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb54'><a id='x1-42018r1'></a><span class='ecrm-0500'>1</span><span id='textcolor1472'><span class='ectt-0800'>/*</span></span> 
@@ -3498,14 +3498,14 @@ $
 <a id='x1-42568r57'></a><span class='ecrm-0500'>57</span> 
 <a id='x1-42570r58'></a><span class='ecrm-0500'>58</span><span class='ectt-0800'>    </span><span id='textcolor1709'><span class='ectt-0800'>return</span></span><span class='ectt-0800'> 0;</span> 
 <a id='x1-42572r59'></a><span class='ecrm-0500'>59</span><span class='ectt-0800'>}</span></pre>
-<!-- l. 1313 --><p class='noindent'>
+<!-- l. 1312 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='completions'><span class='titlemark'>0.11.2   </span> <a id='x1-430000.11.2'></a>Completions</h4>
-<!-- l. 1315 --><p class='noindent'>Sometimes one thing should happen before another within a module having multiple threads.
+<!-- l. 1314 --><p class='noindent'>Sometimes one thing should happen before another within a module having multiple threads.
 Rather than using <code>  <span class='ectt-1000'>/bin/sleep</span>
 </code> commands, the kernel has another way to do this which allows timeouts or
 interrupts to also happen.
-</p><!-- l. 1318 --><p class='indent'>   In the following example two threads are started, but one needs to start before
+</p><!-- l. 1317 --><p class='indent'>   In the following example two threads are started, but one needs to start before
 another.
 </p><!-- l. 1 --><p class='indent'>
                                                                   
@@ -3588,31 +3588,31 @@ another.
 <a id='x1-43149r74'></a><span class='ecrm-0500'>74</span> 
 <a id='x1-43151r75'></a><span class='ecrm-0500'>75</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1760'><span class='ectt-0800'>"Completions example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-43153r76'></a><span class='ecrm-0500'>76</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1761'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1322 --><p class='indent'>   The <code>  <span class='ectt-1000'>machine</span>
+<!-- l. 1321 --><p class='indent'>   The <code>  <span class='ectt-1000'>machine</span>
 </code> structure stores the completion states for the two threads. At the exit
 point of each thread the respective completion state is updated, and
 <code> <span class='ectt-1000'>wait_for_completion</span>
 </code> is used by the flywheel thread to ensure that it does not begin prematurely.
-</p><!-- l. 1325 --><p class='indent'>   So even though <code>  <span class='ectt-1000'>flywheel_thread</span>
+</p><!-- l. 1324 --><p class='indent'>   So even though <code>  <span class='ectt-1000'>flywheel_thread</span>
 </code> is started first you should notice if you load this module and run
 <code> <span class='ectt-1000'>dmesg</span>
 </code> that turning the crank always happens first because the flywheel thread waits for it
 to complete.
-</p><!-- l. 1327 --><p class='indent'>   There are other variations upon the
+</p><!-- l. 1326 --><p class='indent'>   There are other variations upon the
 <code> <span class='ectt-1000'>wait_for_completion</span>
 </code> function, which include timeouts or being interrupted, but this basic mechanism is
 enough for many common situations without adding a lot of complexity.
-</p><!-- l. 1329 --><p class='noindent'>
+</p><!-- l. 1328 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='avoiding-collisions-and-deadlocks'><span class='titlemark'>0.12   </span> <a id='x1-440000.12'></a>Avoiding Collisions and Deadlocks</h3>
-<!-- l. 1331 --><p class='noindent'>If processes running on different CPUs or in different threads try to access the same
+<!-- l. 1330 --><p class='noindent'>If processes running on different CPUs or in different threads try to access the same
 memory, then it is possible that strange things can happen or your system can lock
 up. To avoid this, various types of mutual exclusion kernel functions are available.
 These indicate if a section of code is "locked" or "unlocked" so that simultaneous
 attempts to run it can not happen.
 </p>
    <h4 class='subsectionHead' id='mutex'><span class='titlemark'>0.12.1   </span> <a id='x1-450000.12.1'></a>Mutex</h4>
-<!-- l. 1336 --><p class='noindent'>You can use kernel mutexes (mutual exclusions) in much the same manner that you
+<!-- l. 1335 --><p class='noindent'>You can use kernel mutexes (mutual exclusions) in much the same manner that you
 might deploy them in userland. This may be all that is needed to avoid collisions in
 most cases.
 </p><!-- l. 1 --><p class='indent'>
@@ -3658,18 +3658,18 @@ most cases.
 <a id='x1-45078r39'></a><span class='ecrm-0500'>39</span> 
 <a id='x1-45080r40'></a><span class='ecrm-0500'>40</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1802'><span class='ectt-0800'>"Mutex example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-45082r41'></a><span class='ecrm-0500'>41</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1803'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1341 --><p class='noindent'>
+<!-- l. 1340 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='spinlocks'><span class='titlemark'>0.12.2   </span> <a id='x1-460000.12.2'></a>Spinlocks</h4>
-<!-- l. 1343 --><p class='noindent'>As the name suggests, spinlocks lock up the CPU that the code is running on,
+<!-- l. 1342 --><p class='noindent'>As the name suggests, spinlocks lock up the CPU that the code is running on,
 taking 100% of its resources. Because of this you should only use the spinlock
                                                                   
 
                                                                   
 mechanism around code which is likely to take no more than a few milliseconds to
-run and so will not noticably slow anything down from the user’s point of
+run and so will not noticeably slow anything down from the user’s point of
 view.
-</p><!-- l. 1346 --><p class='indent'>   The example here is <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>"irq safe"</span></span></span> in that if interrupts happen during the lock then
+</p><!-- l. 1345 --><p class='indent'>   The example here is <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>"irq safe"</span></span></span> in that if interrupts happen during the lock then
 they will not be forgotten and will activate when the unlock happens, using the
 <code> <span class='ectt-1000'>flags</span>
 </code> variable to retain their state.
@@ -3738,10 +3738,10 @@ they will not be forgotten and will activate when the unlock happens, using the
 <a id='x1-46123r61'></a><span class='ecrm-0500'>61</span> 
 <a id='x1-46125r62'></a><span class='ecrm-0500'>62</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1858'><span class='ectt-0800'>"Spinlock example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-46127r63'></a><span class='ecrm-0500'>63</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1859'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1350 --><p class='noindent'>
+<!-- l. 1349 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='read-and-write-locks'><span class='titlemark'>0.12.3   </span> <a id='x1-470000.12.3'></a>Read and write locks</h4>
-<!-- l. 1352 --><p class='noindent'>Read and write locks are specialised kinds of spinlocks so that you can exclusively
+<!-- l. 1351 --><p class='noindent'>Read and write locks are specialised kinds of spinlocks so that you can exclusively
 read from something or write to something. Like the earlier spinlocks example, the
 one below shows an "irq safe" situation in which if other functions were triggered
 from irqs which might also read and write to whatever you are concerned with
@@ -3806,14 +3806,14 @@ module.
 <a id='x1-47106r53'></a><span class='ecrm-0500'>53</span> 
 <a id='x1-47108r54'></a><span class='ecrm-0500'>54</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1906'><span class='ectt-0800'>"Read/Write locks example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-47110r55'></a><span class='ecrm-0500'>55</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1907'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1358 --><p class='indent'>   Of course, if you know for sure that there are no functions triggered by irqs
+<!-- l. 1357 --><p class='indent'>   Of course, if you know for sure that there are no functions triggered by irqs
 which could possibly interfere with your logic then you can use the simpler
 <code> <span class='ectt-1000'>read_lock(&amp;myrwlock)</span>
 </code> and <code>  <span class='ectt-1000'>read_unlock(&amp;myrwlock)</span>
 </code> or the corresponding write functions.
 </p>
    <h4 class='subsectionHead' id='atomic-operations'><span class='titlemark'>0.12.4   </span> <a id='x1-480000.12.4'></a>Atomic operations</h4>
-<!-- l. 1361 --><p class='noindent'>If you are doing simple arithmetic: adding, subtracting or bitwise operations, then
+<!-- l. 1360 --><p class='noindent'>If you are doing simple arithmetic: adding, subtracting or bitwise operations, then
 there is another way in the multi-CPU and multi-hyperthreaded world to stop other
 parts of the system from messing with your mojo. By using atomic operations you
 can be confident that your addition, subtraction or bit flip did actually happen
@@ -3898,21 +3898,21 @@ below.
                                                                   
 
                                                                   
-<!-- l. 1368 --><p class='noindent'>
+<!-- l. 1367 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='replacing-print-macros'><span class='titlemark'>0.13   </span> <a id='x1-490000.13'></a>Replacing Print Macros</h3>
-<!-- l. 1370 --><p class='noindent'>
+<!-- l. 1369 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='replacement'><span class='titlemark'>0.13.1   </span> <a id='x1-500000.13.1'></a>Replacement</h4>
-<!-- l. 1372 --><p class='noindent'>In Section <a href='#x1-80042'>2<!-- tex4ht:ref: sec:using_x  --></a>, I said that X Window System and kernel module programming do not
+<!-- l. 1371 --><p class='noindent'>In Section <a href='#x1-80042'>2<!-- tex4ht:ref: sec:using_x  --></a>, I said that X Window System and kernel module programming do not
 mix. That is true for developing kernel modules. But in actual use, you want to be
 able to send messages to whichever tty the command to load the module came
 from.
-</p><!-- l. 1376 --><p class='indent'>   "tty" is an abbreviation of <span class='ecti-1000'>teletype</span>: originally a combination keyboard-printer
+</p><!-- l. 1375 --><p class='indent'>   "tty" is an abbreviation of <span class='ecti-1000'>teletype</span>: originally a combination keyboard-printer
 used to communicate with a Unix system, and today an abstraction for the text
 stream used for a Unix program, whether it is a physical terminal, an xterm on an X
 display, a network connection used with ssh, etc.
-</p><!-- l. 1378 --><p class='indent'>   The way this is done is by using current, a pointer to the currently running task,
+</p><!-- l. 1377 --><p class='indent'>   The way this is done is by using current, a pointer to the currently running task,
 to get the current task’s tty structure. Then, we look inside that tty structure to find
 a pointer to a string write function, which we use to write a string to the
 tty.
@@ -3995,16 +3995,16 @@ tty.
 <a id='x1-50150r75'></a><span class='ecrm-0500'>75</span><span class='ectt-0800'>module_exit(print_string_exit);</span> 
 <a id='x1-50152r76'></a><span class='ecrm-0500'>76</span> 
 <a id='x1-50154r77'></a><span class='ecrm-0500'>77</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2032'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1383 --><p class='noindent'>
+<!-- l. 1382 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='flashing-keyboard-leds'><span class='titlemark'>0.13.2   </span> <a id='x1-510000.13.2'></a>Flashing keyboard LEDs</h4>
-<!-- l. 1385 --><p class='noindent'>In certain conditions, you may desire a simpler and more direct way to communicate
+<!-- l. 1384 --><p class='noindent'>In certain conditions, you may desire a simpler and more direct way to communicate
 to the external world. Flashing keyboard LEDs can be such a solution: It is an
 immediate way to attract attention or to display a status condition. Keyboard LEDs
 are present on every hardware, they are always visible, they do not need any setup,
 and their use is rather simple and non-intrusive, compared to writing to a tty or a
 file.
-</p><!-- l. 1389 --><p class='indent'>   The following source code illustrates a minimal kernel module which, when
+</p><!-- l. 1388 --><p class='indent'>   The following source code illustrates a minimal kernel module which, when
 loaded, starts blinking the keyboard LEDs until it is unloaded.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4100,7 +4100,7 @@ loaded, starts blinking the keyboard LEDs until it is unloaded.
                                                                   
 
                                                                   
-<!-- l. 1393 --><p class='indent'>   If none of the examples in this chapter fit your debugging needs,
+<!-- l. 1392 --><p class='indent'>   If none of the examples in this chapter fit your debugging needs,
 there might yet be some other tricks to try. Ever wondered what
 <code> <span class='ectt-1000'>CONFIG_LL_DEBUG</span>
 </code> in <code>  <span class='ectt-1000'>make menuconfig</span>
@@ -4111,22 +4111,22 @@ everything what your code does over a serial line. If you find yourself porting
 kernel to some new and former unsupported architecture, this is usually amongst the
 first things that should be implemented. Logging over a netconsole might also be
 worth a try.
-</p><!-- l. 1400 --><p class='indent'>   While you have seen lots of stuff that can be used to aid debugging here, there are
+</p><!-- l. 1399 --><p class='indent'>   While you have seen lots of stuff that can be used to aid debugging here, there are
 some things to be aware of. Debugging is almost always intrusive. Adding debug code
 can change the situation enough to make the bug seem to dissappear. Thus you
 should try to keep debug code to a minimum and make sure it does not show up in
 production code.
-</p><!-- l. 1404 --><p class='noindent'>
+</p><!-- l. 1403 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='scheduling-tasks'><span class='titlemark'>0.14   </span> <a id='x1-520000.14'></a>Scheduling Tasks</h3>
-<!-- l. 1406 --><p class='noindent'>There are two main ways of running tasks: tasklets and work queues. Tasklets are a
+<!-- l. 1405 --><p class='noindent'>There are two main ways of running tasks: tasklets and work queues. Tasklets are a
 quick and easy way of scheduling a single function to be run. For example, when
 triggered from an interrupt, whereas work queues are more complicated but also
 better suited to running multiple things in a sequence.
-</p><!-- l. 1410 --><p class='noindent'>
+</p><!-- l. 1409 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='tasklets'><span class='titlemark'>0.14.1   </span> <a id='x1-530000.14.1'></a>Tasklets</h4>
-<!-- l. 1412 --><p class='noindent'>Here is an example tasklet module. The
+<!-- l. 1411 --><p class='noindent'>Here is an example tasklet module. The
 <code> <span class='ectt-1000'>tasklet_fn</span>
 </code> function runs for a few seconds and in the mean time execution of the
 <code> <span class='ectt-1000'>example_tasklet_init</span>
@@ -4170,7 +4170,7 @@ better suited to running multiple things in a sequence.
 <a id='x1-53072r35'></a><span class='ecrm-0500'>35</span> 
 <a id='x1-53074r36'></a><span class='ecrm-0500'>36</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2152'><span class='ectt-0800'>"Tasklet example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-53076r37'></a><span class='ecrm-0500'>37</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2153'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1417 --><p class='indent'>   So with this example loaded <code>  <span class='ectt-1000'>dmesg</span>
+<!-- l. 1416 --><p class='indent'>   So with this example loaded <code>  <span class='ectt-1000'>dmesg</span>
 </code> should show:
                                                                   
 
@@ -4182,11 +4182,11 @@ Example tasklet starts
 Example tasklet init continues...
 Example tasklet ends
 </pre>
-<!-- l. 1424 --><p class='nopar'>
+<!-- l. 1423 --><p class='nopar'>
-</p><!-- l. 1426 --><p class='noindent'>
+</p><!-- l. 1425 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='work-queues'><span class='titlemark'>0.14.2   </span> <a id='x1-540000.14.2'></a>Work queues</h4>
-<!-- l. 1428 --><p class='noindent'>To add a task to the scheduler we can use a workqueue. The kernel then uses the
+<!-- l. 1427 --><p class='noindent'>To add a task to the scheduler we can use a workqueue. The kernel then uses the
 Completely Fair Scheduler (CFS) to execute work within the queue.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4224,19 +4224,19 @@ Completely Fair Scheduler (CFS) to execute work within the queue.
 <a id='x1-54064r32'></a><span class='ecrm-0500'>32</span> 
 <a id='x1-54066r33'></a><span class='ecrm-0500'>33</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2181'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-54068r34'></a><span class='ecrm-0500'>34</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2182'><span class='ectt-0800'>"Workqueue example"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1433 --><p class='noindent'>
+<!-- l. 1432 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='interrupt-handlers'><span class='titlemark'>0.15   </span> <a id='x1-550000.15'></a>Interrupt Handlers</h3>
-<!-- l. 1435 --><p class='noindent'>
+<!-- l. 1434 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='interrupt-handlers1'><span class='titlemark'>0.15.1   </span> <a id='x1-560000.15.1'></a>Interrupt Handlers</h4>
-<!-- l. 1437 --><p class='noindent'>Except for the last chapter, everything we did in the kernel so far we have done as a
+<!-- l. 1436 --><p class='noindent'>Except for the last chapter, everything we did in the kernel so far we have done as a
 response to a process asking for it, either by dealing with a special file, sending an
 <code> <span class='ectt-1000'>ioctl()</span>
 </code>, or issuing a system call. But the job of the kernel is not just to respond to process
 requests. Another job, which is every bit as important, is to speak to the hardware
 connected to the machine.
-</p><!-- l. 1441 --><p class='indent'>   There are two types of interaction between the CPU and the rest of the
+</p><!-- l. 1440 --><p class='indent'>   There are two types of interaction between the CPU and the rest of the
 computer’s hardware. The first type is when the CPU gives orders to the hardware,
 the order is when the hardware needs to tell the CPU something. The second, called
 interrupts, is much harder to implement because it has to be dealt with when
@@ -4246,14 +4246,14 @@ lost.
                                                                   
 
                                                                   
-</p><!-- l. 1446 --><p class='indent'>   Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
+</p><!-- l. 1445 --><p class='indent'>   Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
 are two types of IRQ’s, short and long. A short IRQ is one which is expected to take
 a very short period of time, during which the rest of the machine will be blocked and
 no other interrupts will be handled. A long IRQ is one which can take longer, and
 during which other interrupts may occur (but not interrupts from the same
 device). If at all possible, it is better to declare an interrupt handler to be
 long.
-</p><!-- l. 1452 --><p class='indent'>   When the CPU receives an interrupt, it stops whatever it is doing (unless it is
+</p><!-- l. 1451 --><p class='indent'>   When the CPU receives an interrupt, it stops whatever it is doing (unless it is
 processing a more important interrupt, in which case it will deal with this one
 only when the more important one is done), saves certain parameters on
 the stack and calls the interrupt handler. This means that certain things
@@ -4265,10 +4265,10 @@ the new information at a later time (this is called the "bottom half") and
 return. The kernel is then guaranteed to call the bottom half as soon as
 possible – and when it does, everything allowed in kernel modules will be
 allowed.
-</p><!-- l. 1458 --><p class='indent'>   The way to implement this is to call
+</p><!-- l. 1457 --><p class='indent'>   The way to implement this is to call
 <code> <span class='ectt-1000'>request_irq()</span>
 </code> to get your interrupt handler called when the relevant IRQ is received.
-</p><!-- l. 1460 --><p class='indent'>   In practice IRQ handling can be a bit more complex. Hardware is often
+</p><!-- l. 1459 --><p class='indent'>   In practice IRQ handling can be a bit more complex. Hardware is often
 designed in a way that chains two interrupt controllers, so that all the IRQs
 from interrupt controller B are cascaded to a certain IRQ from interrupt
 controller A. Of course, that requires that the kernel finds out which IRQ it
@@ -4278,11 +4278,11 @@ them requires handlers to be written in assembler, so they do not really
 fit into the kernel. They can be made to work similar to the others, but
 after that procedure, they are no longer any faster than "common" IRQs.
 SMP enabled kernels running on systems with more than one processor
-need to solve another truckload of problems. It is not enough to know if
+need to solve another truckload of problems. It is not enough to know if a
-a certain IRQs has happend, it’s also important for what CPU(s) it was
+certain IRQs has happened, it’s also important to know what CPU(s) it was
 for. People still interested in more details, might want to refer to "APIC"
 now.
-</p><!-- l. 1469 --><p class='indent'>   This function receives the IRQ number, the name of the function,
+</p><!-- l. 1468 --><p class='indent'>   This function receives the IRQ number, the name of the function,
 flags, a name for <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/interrupts</span></span></span> and a parameter to be passed to the
 interrupt handler. Usually there is a certain number of IRQs available.
 How many IRQs there are is hardware-dependent. The flags can include
@@ -4295,16 +4295,16 @@ already a handler on this IRQ, or if you are both willing to share.
                                                                   
 
                                                                   
-</p><!-- l. 1475 --><p class='noindent'>
+</p><!-- l. 1474 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='detecting-button-presses'><span class='titlemark'>0.15.2   </span> <a id='x1-570000.15.2'></a>Detecting button presses</h4>
-<!-- l. 1477 --><p class='noindent'>Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
+<!-- l. 1476 --><p class='noindent'>Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
 bunch of GPIO pins. Attaching buttons to those and then having a button press do
 something is a classic case in which you might need to use interrupts, so that instead
 of having the CPU waste time and battery power polling for a change in input state,
 it is better for the input to trigger the CPU to then run a particular handling
 function.
-</p><!-- l. 1481 --><p class='indent'>   Here is an example where buttons are connected to GPIO numbers 17 and 18 and
+</p><!-- l. 1480 --><p class='indent'>   Here is an example where buttons are connected to GPIO numbers 17 and 18 and
 an LED is connected to GPIO 4. You can change those numbers to whatever is
 appropriate for your board.
 </p><!-- l. 1 --><p class='indent'>
@@ -4454,14 +4454,14 @@ appropriate for your board.
 <a id='x1-57286r143'></a><span class='ecrm-0500'>143</span> 
 <a id='x1-57288r144'></a><span class='ecrm-0500'>144</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2289'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-57290r145'></a><span class='ecrm-0500'>145</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2290'><span class='ectt-0800'>"Handle some GPIO interrupts"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1486 --><p class='noindent'>
+<!-- l. 1485 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='bottom-half'><span class='titlemark'>0.15.3   </span> <a id='x1-580000.15.3'></a>Bottom Half</h4>
-<!-- l. 1488 --><p class='noindent'>Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
+<!-- l. 1487 --><p class='noindent'>Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
 way to do that without rendering the interrupt unavailable for a significant duration
 is to combine it with a tasklet. This pushes the bulk of the work off into the
 scheduler.
-</p><!-- l. 1492 --><p class='indent'>   The example below modifies the previous example to also run an additional task
+</p><!-- l. 1491 --><p class='indent'>   The example below modifies the previous example to also run an additional task
 when an interrupt is triggered.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4626,10 +4626,10 @@ when an interrupt is triggered.
 <a id='x1-58318r159'></a><span class='ecrm-0500'>159</span> 
 <a id='x1-58320r160'></a><span class='ecrm-0500'>160</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2411'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-58322r161'></a><span class='ecrm-0500'>161</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2412'><span class='ectt-0800'>"Interrupt with top and bottom half"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1496 --><p class='noindent'>
+<!-- l. 1495 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='crypto'><span class='titlemark'>0.16   </span> <a id='x1-590000.16'></a>Crypto</h3>
-<!-- l. 1498 --><p class='noindent'>At the dawn of the internet, everybody trusted everybody completely…but that did
+<!-- l. 1497 --><p class='noindent'>At the dawn of the internet, everybody trusted everybody completely…but that did
 not work out so well. When this guide was originally written, it was a more innocent
 era in which almost nobody actually gave a damn about crypto - least of all kernel
 developers. That is certainly no longer the case now. To handle crypto stuff, the
@@ -4638,10 +4638,10 @@ favourite hash functions.
                                                                   
 
                                                                   
-</p><!-- l. 1503 --><p class='noindent'>
+</p><!-- l. 1502 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='hash-functions'><span class='titlemark'>0.16.1   </span> <a id='x1-600000.16.1'></a>Hash functions</h4>
-<!-- l. 1506 --><p class='noindent'>Calculating and checking the hashes of things is a common operation. Here is a
+<!-- l. 1505 --><p class='noindent'>Calculating and checking the hashes of things is a common operation. Here is a
 demonstration of how to calculate a sha256 hash within a kernel module.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4707,21 +4707,21 @@ demonstration of how to calculate a sha256 hash within a kernel module.
 <a id='x1-60120r60'></a><span class='ecrm-0500'>60</span> 
 <a id='x1-60122r61'></a><span class='ecrm-0500'>61</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2462'><span class='ectt-0800'>"sha256 hash test"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-60124r62'></a><span class='ecrm-0500'>62</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2463'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1511 --><p class='indent'>   Make and install the module:
+<!-- l. 1510 --><p class='indent'>   Make and install the module:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb68'><a id='x1-60129r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>make</span> 
 <a id='x1-60131r2'></a><span class='ecrm-0500'>2</span><span class='ectt-1000'>sudo insmod cryptosha256.ko</span> 
 <a id='x1-60133r3'></a><span class='ecrm-0500'>3</span><span class='ectt-1000'>dmesg</span></pre>
-<!-- l. 1519 --><p class='indent'>   And you should see that the hash was calculated for the test string.
+<!-- l. 1518 --><p class='indent'>   And you should see that the hash was calculated for the test string.
-</p><!-- l. 1521 --><p class='indent'>   Finally, remove the test module:
+</p><!-- l. 1520 --><p class='indent'>   Finally, remove the test module:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb69'><a id='x1-60136r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>sudo rmmod cryptosha256</span></pre>
-<!-- l. 1527 --><p class='noindent'>
+<!-- l. 1526 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='symmetric-key-encryption'><span class='titlemark'>0.16.2   </span> <a id='x1-610000.16.2'></a>Symmetric key encryption</h4>
-<!-- l. 1529 --><p class='noindent'>Here is an example of symmetrically encrypting a string using the AES algorithm
+<!-- l. 1528 --><p class='noindent'>Here is an example of symmetrically encrypting a string using the AES algorithm
 and a password.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4922,13 +4922,13 @@ and a password.
 <a id='x1-61390r195'></a><span class='ecrm-0500'>195</span> 
 <a id='x1-61392r196'></a><span class='ecrm-0500'>196</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2609'><span class='ectt-0800'>"Symmetric key encryption example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-61394r197'></a><span class='ecrm-0500'>197</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2610'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1533 --><p class='noindent'>
+<!-- l. 1532 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='standardizing-the-interfaces-the-device-model'><span class='titlemark'>0.17   </span> <a id='x1-620000.17'></a>Standardizing the interfaces: The Device Model</h3>
-<!-- l. 1535 --><p class='noindent'>Up to this point we have seen all kinds of modules doing all kinds of things, but there
+<!-- l. 1534 --><p class='noindent'>Up to this point we have seen all kinds of modules doing all kinds of things, but there
 was no consistency in their interfaces with the rest of the kernel. To impose some
 consistency such that there is at minimum a standardized way to start, suspend and
-resume a device a device model was added. An example is show below, and you can
+resume a device a device model was added. An example is shown below, and you can
 use this as a template to add your own suspend, resume or other interface
 functions.
 </p><!-- l. 1 --><p class='indent'>
@@ -5035,24 +5035,23 @@ functions.
                                                                   
 
                                                                   
-<!-- l. 1541 --><p class='noindent'>
+<!-- l. 1540 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='optimizations'><span class='titlemark'>0.18   </span> <a id='x1-630000.18'></a>Optimizations</h3>
-<!-- l. 1543 --><p class='noindent'>
+<!-- l. 1542 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='likely-and-unlikely-conditions'><span class='titlemark'>0.18.1   </span> <a id='x1-640000.18.1'></a>Likely and Unlikely conditions</h4>
-<!-- l. 1545 --><p class='noindent'>Sometimes you might want your code to run as quickly as possible,
+<!-- l. 1544 --><p class='noindent'>Sometimes you might want your code to run as quickly as possible,
 especially if it is handling an interrupt or doing something which might
-cause noticible latency. If your code contains boolean conditions and if you
+cause noticeable latency. If your code contains boolean conditions and if
-know that the conditions are almost always likely to evaluate as either
+you know that the conditions are almost always likely to evaluate as either
 <code> <span class='ectt-1000'>true</span>
 </code> or <code>  <span class='ectt-1000'>false</span>
 </code>, then you can allow the compiler to optimize for this using the
 <code> <span class='ectt-1000'>likely</span>
 </code> and <code>  <span class='ectt-1000'>unlikely</span>
-</code> macros.
+</code> macros. For example, when allocating memory you are almost always expecting this
-</p><!-- l. 1549 --><p class='indent'>   For example, when allocating memory you are almost always expecting this to
+to succeed.
-succeed.
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb72'><a id='x1-64012r1'></a><span class='ecrm-0500'>1</span><span class='ectt-0800'>bvl = bvec_alloc(gfp_mask, nr_iovecs, &amp;idx);</span> 
@@ -5061,50 +5060,50 @@ succeed.
 <a id='x1-64018r4'></a><span class='ecrm-0500'>4</span><span class='ectt-0800'>    bio = NULL;</span> 
 <a id='x1-64020r5'></a><span class='ecrm-0500'>5</span><span class='ectt-0800'>    </span><span id='textcolor2688'><span class='ectt-0800'>goto</span></span><span class='ectt-0800'> out;</span> 
 <a id='x1-64022r6'></a><span class='ecrm-0500'>6</span><span class='ectt-0800'>}</span></pre>
-<!-- l. 1560 --><p class='indent'>   When the <code>  <span class='ectt-1000'>unlikely</span>
+<!-- l. 1558 --><p class='indent'>   When the <code>  <span class='ectt-1000'>unlikely</span>
 </code> macro is used, the compiler alters its machine instruction output, so that it
 continues along the false branch and only jumps if the condition is true. That
 avoids flushing the processor pipeline. The opposite happens if you use the
 <code> <span class='ectt-1000'>likely</span>
 </code> macro.
-</p><!-- l. 1564 --><p class='noindent'>
+</p><!-- l. 1562 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='common-pitfalls'><span class='titlemark'>0.19   </span> <a id='x1-650000.19'></a>Common Pitfalls</h3>
-<!-- l. 1567 --><p class='noindent'>
+<!-- l. 1565 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='using-standard-libraries'><span class='titlemark'>0.19.1   </span> <a id='x1-660000.19.1'></a>Using standard libraries</h4>
-<!-- l. 1569 --><p class='noindent'>You can not do that. In a kernel module, you can only use kernel functions which are
+<!-- l. 1567 --><p class='noindent'>You can not do that. In a kernel module, you can only use kernel functions which are
 the functions you can see in <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/kallsyms</span></span></span>.
                                                                   
 
                                                                   
-</p><!-- l. 1572 --><p class='noindent'>
+</p><!-- l. 1570 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='disabling-interrupts'><span class='titlemark'>0.19.2   </span> <a id='x1-670000.19.2'></a>Disabling interrupts</h4>
-<!-- l. 1574 --><p class='noindent'>You might need to do this for a short time and that is OK, but if you do not enable
+<!-- l. 1572 --><p class='noindent'>You might need to do this for a short time and that is OK, but if you do not enable
 them afterwards, your system will be stuck and you will have to power it
 off.
-</p><!-- l. 1576 --><p class='noindent'>
+</p><!-- l. 1574 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='where-to-go-from-here'><span class='titlemark'>0.20   </span> <a id='x1-680000.20'></a>Where To Go From Here?</h3>
-<!-- l. 1578 --><p class='noindent'>For people seriously interested in kernel programming, I recommend <a href='https://kernelnewbies.org'>kernelnewbies.org</a>
+<!-- l. 1576 --><p class='noindent'>For people seriously interested in kernel programming, I recommend <a href='https://kernelnewbies.org'>kernelnewbies.org</a>
 and the <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation'>Documentation</a> subdirectory within the kernel source code which is not
 always easy to understand but can be a starting point for further investigation. Also,
 as Linus Torvalds said, the best way to learn the kernel is to read the source code
 yourself.
-</p><!-- l. 1581 --><p class='indent'>   If you are interested in more examples of short kernel modules then searching on
+</p><!-- l. 1579 --><p class='indent'>   If you are interested in more examples of short kernel modules then searching on
 sites such as Github and Gitlab is a good way to start, although there is a lot of
 duplication of older LKMPG examples which may not compile with newer kernel
 versions. You will also be able to find examples of the use of kernel modules to attack
 or compromise systems or exfiltrate data and those can be useful for thinking about
 how to defend systems and learning about existing security mechanisms within the
 kernel.
-</p><!-- l. 1584 --><p class='indent'>   I hope I have helped you in your quest to become a better programmer, or at
+</p><!-- l. 1582 --><p class='indent'>   I hope I have helped you in your quest to become a better programmer, or at
 least to have fun through technology. And, if you do write useful kernel modules, I
 hope you publish them under the GPL, so I can use them too.
-</p><!-- l. 1587 --><p class='indent'>   If you would like to contribute to this guide or notice anything glaringly wrong,
+</p><!-- l. 1585 --><p class='indent'>   If you would like to contribute to this guide or notice anything glaringly wrong,
 please create an issue at <a class='url' href='https://github.com/sysprog21/lkmpg'><span class='ectt-1000'>https://github.com/sysprog21/lkmpg</span></a>.
-</p><!-- l. 1589 --><p class='indent'>   Happy hacking!
+</p><!-- l. 1587 --><p class='indent'>   Happy hacking!
 </p>
     
 </body> 

lkmpg-for-ht.html

@@ -17,7 +17,7 @@
 
 <h2 class='titleHead'>The Linux Kernel Module Programming Guide</h2>
 <div class='author'><span class='ecrm-1200'>Peter Jay Salzman, Michael Burian, Ori Pomerantz, Bob Mottram, Jim Huang</span></div><br />
-<div class='date'><span class='ecrm-1200'>August 16, 2021</span></div>
+<div class='date'><span class='ecrm-1200'>August 17, 2021</span></div>
                                                                   
 
                                                                   
@@ -280,7 +280,7 @@ module.
    <pre class='fancyvrb' id='fancyvrb10'><a id='x1-12008r1'></a><span class='ecrm-0500'>1</span><span id='textcolor3'><span class='ectt-0800'>/*</span></span> 
 <a id='x1-12010r2'></a><span class='ecrm-0500'>2</span><span id='textcolor4'><span class='ectt-0800'> * hello-1.c - The simplest kernel module.</span></span> 
 <a id='x1-12012r3'></a><span class='ecrm-0500'>3</span><span id='textcolor5'><span class='ectt-0800'> */</span></span> 
-<a id='x1-12014r4'></a><span class='ecrm-0500'>4</span><span id='textcolor6'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor7'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-12014r4'></a><span class='ecrm-0500'>4</span><span id='textcolor6'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor7'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-12016r5'></a><span class='ecrm-0500'>5</span><span id='textcolor8'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor9'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-12018r6'></a><span class='ecrm-0500'>6</span> 
 <a id='x1-12020r7'></a><span class='ecrm-0500'>7</span><span id='textcolor10'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> init_module(</span><span id='textcolor11'><span class='ectt-0800'>void</span></span><span class='ectt-0800'>)</span> 
@@ -425,7 +425,7 @@ technique:
 <a id='x1-13010r3'></a><span class='ecrm-0500'>3</span><span id='textcolor30'><span class='ectt-0800'> * This is preferred over using init_module() and cleanup_module().</span></span> 
 <a id='x1-13012r4'></a><span class='ecrm-0500'>4</span><span id='textcolor31'><span class='ectt-0800'> */</span></span> 
 <a id='x1-13014r5'></a><span class='ecrm-0500'>5</span><span id='textcolor32'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor33'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-13016r6'></a><span class='ecrm-0500'>6</span><span id='textcolor34'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor35'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-13016r6'></a><span class='ecrm-0500'>6</span><span id='textcolor34'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor35'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-13018r7'></a><span class='ecrm-0500'>7</span><span id='textcolor36'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor37'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-13020r8'></a><span class='ecrm-0500'>8</span> 
 <a id='x1-13022r9'></a><span class='ecrm-0500'>9</span><span id='textcolor38'><span class='ectt-0800'>static</span></span><span class='ectt-0800'> </span><span id='textcolor39'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> __init hello_2_init(</span><span id='textcolor40'><span class='ectt-0800'>void</span></span><span class='ectt-0800'>)</span> 
@@ -462,7 +462,7 @@ is as simple as this:
 see, some things get hardwired into the kernel (<span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-y</span></span></span>) but where are all those <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-m</span></span></span>
 gone? Those familiar with shell scripts will easily be able to spot them. For those not,
 the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-$(CONFIG_FOO)</span></span></span> entries you see everywhere expand into <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-y</span></span></span> or <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>obj-m</span></span></span>,
-depending on whether the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>CONFIG_FOO</span></span></span> variable has been set to y or m. While we are
+depending on whether the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>CONFIG_FOO</span></span></span> variable has been set to <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>y</span></span></span> or <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>m</span></span></span>. While we are
 at it, those were exactly the kind of variables that you have set in the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>.config</span></span></span> file in
 the top-level directory of Linux kernel source tree, the last time when you said
 <code> <span class='ectt-1000'>make menuconfig</span>
@@ -494,7 +494,7 @@ memory: 236k freed, this is precisely what the kernel is freeing.
 <a id='x1-14009r2'></a><span class='ecrm-0500'>2</span><span id='textcolor57'><span class='ectt-0800'> * hello-3.c - Illustrating the __init, __initdata and __exit macros.</span></span> 
 <a id='x1-14011r3'></a><span class='ecrm-0500'>3</span><span id='textcolor58'><span class='ectt-0800'> */</span></span> 
 <a id='x1-14013r4'></a><span class='ecrm-0500'>4</span><span id='textcolor59'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor60'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-14015r5'></a><span class='ecrm-0500'>5</span><span id='textcolor61'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor62'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-14015r5'></a><span class='ecrm-0500'>5</span><span id='textcolor61'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor62'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-14017r6'></a><span class='ecrm-0500'>6</span><span id='textcolor63'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor64'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-14019r7'></a><span class='ecrm-0500'>7</span> 
 <a id='x1-14021r8'></a><span class='ecrm-0500'>8</span><span id='textcolor65'><span class='ectt-0800'>static</span></span><span class='ectt-0800'> </span><span id='textcolor66'><span class='ectt-0800'>int</span></span><span class='ectt-0800'> hello3_data __initdata = 3;</span> 
@@ -543,7 +543,7 @@ example.
 <a id='x1-15005r2'></a><span class='ecrm-0500'>2</span><span id='textcolor82'><span class='ectt-0800'> * hello-4.c - Demonstrates module documentation.</span></span> 
 <a id='x1-15007r3'></a><span class='ecrm-0500'>3</span><span id='textcolor83'><span class='ectt-0800'> */</span></span> 
 <a id='x1-15009r4'></a><span class='ecrm-0500'>4</span><span id='textcolor84'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor85'><span class='ectt-0800'>&lt;linux/init.h&gt;   /* Needed for the macros */</span></span> 
-<a id='x1-15011r5'></a><span class='ecrm-0500'>5</span><span id='textcolor86'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor87'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for KERN_INFO */</span></span> 
+<a id='x1-15011r5'></a><span class='ecrm-0500'>5</span><span id='textcolor86'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor87'><span class='ectt-0800'>&lt;linux/kernel.h&gt; /* Needed for pr_info() */</span></span> 
 <a id='x1-15013r6'></a><span class='ecrm-0500'>6</span><span id='textcolor88'><span class='ectt-0800'>#include</span></span><span class='ectt-0800'> </span><span id='textcolor89'><span class='ectt-0800'>&lt;linux/module.h&gt; /* Needed by all modules */</span></span> 
 <a id='x1-15015r7'></a><span class='ecrm-0500'>7</span> 
 <a id='x1-15017r8'></a><span class='ecrm-0500'>8</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor90'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
@@ -800,7 +800,7 @@ error as follows:
 insmod: error inserting 'poet_atkm.ko': -1 Invalid module format
 </pre>
 <!-- l. 489 --><p class='nopar'>
-</p><!-- l. 491 --><p class='indent'>   Less cryptical information are logged to the systemd journal:
+</p><!-- l. 491 --><p class='indent'>   Less cryptic information is logged to the systemd journal:
                                                                   
 
                                                                   
@@ -833,8 +833,8 @@ name:           hello_4
 vermagic:       5.4.0-70-generic SMP mod_unload modversions
 </pre>
 <!-- l. 513 --><p class='nopar'>
-</p><!-- l. 515 --><p class='indent'>   To overcome this problem we could resort to the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>--force-vermagic</span></span></span>
+</p><!-- l. 515 --><p class='indent'>   To overcome this problem we could resort to the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>--force-vermagic</span></span></span> option,
-option, but this solution is potentially unsafe, and unquestionably inacceptable
+but this solution is potentially unsafe, and unquestionably unacceptable
 in production modules. Consequently, we want to compile our module in
 an environment which was identical to the one in which our precompiled
 kernel was built. How to do this, is the subject of the remainder of this
@@ -847,11 +847,11 @@ tree: <code>  <span class='ectt-1000'>cp /boot/config-</span><span id='textcolo
 </code>.
 </p><!-- l. 524 --><p class='indent'>   Let’s focus again on the previous error message: a closer look at the version magic
 strings suggests that, even with two configuration files which are exactly the same, a
-slight difference in the version magic could be possible, and it is sufficient to
+slight difference in the version magic could be possible, and it is sufficient to prevent
-prevent insertion of the module into the kernel. That slight difference, namely
+insertion of the module into the kernel. That slight difference, namely the
-the custom string which appears in the module’s version magic and not in
+custom string which appears in the module’s version magic and not in the
-the kernel’s one, is due to a modification with respect to the original, in
+kernel’s one, is due to a modification with respect to the original, in the
-the makefile that some distribution include. Then, examine your <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>Makefile</span></span></span>,
+makefile that some distributions include. Then, examine your <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>Makefile</span></span></span>,
 and make sure that the specified version information matches exactly the
 one used for your current kernel. For example, you makefile could start as
 follows:
@@ -974,7 +974,7 @@ data into strings and write the string data using the low-level system call
 <a id='x1-21026r6'></a><span class='ecrm-0500'>6</span><span class='ectt-0800'>    </span><span id='textcolor262'><span class='ectt-0800'>return</span></span><span class='ectt-0800'> 0;</span> 
 <a id='x1-21028r7'></a><span class='ecrm-0500'>7</span><span class='ectt-0800'>}</span></pre>
 <!-- l. 608 --><p class='indent'>   with <code>  <span class='ectt-1000'>gcc -Wall -o hello hello.c</span>
-</code>. Run the exectable with <code>  <span class='ectt-1000'>strace ./hello</span>
+</code>. Run the executable with <code>  <span class='ectt-1000'>strace ./hello</span>
 </code>. Are you impressed? Every line you see corresponds to a system call. <a href='https://strace.io/'>strace</a> is a
 handy program that gives you details about what system calls a program is
 making, including which call is made, what its arguments are and what it
@@ -1036,8 +1036,8 @@ symbols.
 entire kernel, so this is definitely an issue. The best way to deal with this is to declare
 all your variables as static and to use a well-defined prefix for your symbols. By
 convention, all kernel prefixes are lowercase. If you do not want to declare everything
-as static, another option is to declare a symbol table and register it with a kernel. We
+as static, another option is to declare a symbol table and register it with the kernel.
-will get to this later.
+We will get to this later.
 </p><!-- l. 652 --><p class='indent'>   The file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/kallsyms</span></span></span> holds all the symbols that the kernel knows about and
 which are therefore accessible to your modules since they share the kernel’s
 codespace.
@@ -1583,7 +1583,7 @@ conditional compilation directives. The way to do this to compare the macro
 information to processes — the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> file system. Originally designed to allow easy
 access to information about processes (hence the name), it is now used by every bit
 of the kernel which has something interesting to report, such as <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/modules</span></span></span>
-which provides the list of modules and <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/meminfo</span></span></span> which stats memory usage
+which provides the list of modules and <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/meminfo</span></span></span> which gathers memory usage
 statistics.
 </p><!-- l. 943 --><p class='indent'>   The method to use the proc file system is very similar to the one used with device
 drivers — a structure is created with all the information needed for the <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> file,
@@ -1620,7 +1620,7 @@ function <code>  <span class='ectt-1000'>procfile_read</span>
 </code>. The return value is a <code>  <span id='textcolor548'><span class='ectt-1000'>struct</span></span><span class='ectt-1000'> proc_dir_entry</span>
 </code>, and it will be used to configure the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> (for example, the owner
 of this file). A null return value means that the creation has failed.
-</p><!-- l. 959 --><p class='indent'>   Each time, everytime the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> is read, the function
+</p><!-- l. 959 --><p class='indent'>   Every time the file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/helloworld</span></span></span> is read, the function
 <code> <span class='ectt-1000'>procfile_read</span>
 </code> is called. Two parameters of this function are very important: the buffer
 (the second parameter) and the offset (the fourth one). The content of the
@@ -2200,7 +2200,7 @@ the same way as in the previous example.
 <!-- l. 1076 --><p class='indent'>   If you want more information, you can read this web page:
 </p>
      <ul class='itemize1'>
-     <li class='itemize'><a class='url' href='http://lwn.net/Articles/22355/'><span class='ectt-1000'>http://lwn.net/Articles/22355/</span></a>
+     <li class='itemize'><a class='url' href='https://lwn.net/Articles/22355/'><span class='ectt-1000'>https://lwn.net/Articles/22355/</span></a>
      </li>
      <li class='itemize'><a class='url' href='https://kernelnewbies.org/Documents/SeqFileHowTo'><span class='ectt-1000'>https://kernelnewbies.org/Documents/SeqFileHowTo</span></a></li></ul>
 <!-- l. 1083 --><p class='indent'>   You can also read the code of <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/fs/seq_file.c'>fs/seq_file.c</a> in the linux kernel.
@@ -2327,7 +2327,7 @@ device file to write things to the modem (either modem commands or data to
 be sent through the phone line) and read things from the modem (either
 responses for commands or the data received through the phone line). However,
 this leaves open the question of what to do when you need to talk to the
-serial port itself, for example to send the rate at which data is sent and
+serial port itself, for example to configure the rate at which data is sent and
 received.
                                                                   
 
@@ -2360,7 +2360,7 @@ ioctl.c.
 </p><!-- l. 1155 --><p class='indent'>   If you want to use ioctls in your own kernel modules, it is best to receive an
 official ioctl assignment, so if you accidentally get somebody else’s ioctls, or if they
 get yours, you’ll know something is wrong. For more information, consult the kernel
-source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/driver-api/ioctl.rst'>Documentation/driver-api/ioctl.rst</a>.
+source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/userspace-api/ioctl/ioctl-number.rst'>Documentation/userspace-api/ioctl/ioctl-number.rst</a>.
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb49'><a id='x1-39009r1'></a><span class='ecrm-0500'>1</span><span id='textcolor964'><span class='ectt-0800'>/*</span></span> 
@@ -2843,30 +2843,30 @@ source tree at <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/l
 <a id='x1-39951r196'></a><span class='ecrm-0500'>196</span> 
 <a id='x1-39953r197'></a><span class='ecrm-0500'>197</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1336'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-39955r198'></a><span class='ecrm-0500'>198</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1337'><span class='ectt-0800'>"This is test_ioctl module"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1165 --><p class='noindent'>
+<!-- l. 1164 --><p class='noindent'>
 </p>
                                                                   
 
                                                                   
    <h3 class='sectionHead' id='system-calls'><span class='titlemark'>0.10   </span> <a id='x1-400000.10'></a>System Calls</h3>
-<!-- l. 1167 --><p class='noindent'>So far, the only thing we’ve done was to use well defined kernel mechanisms to
+<!-- l. 1166 --><p class='noindent'>So far, the only thing we’ve done was to use well defined kernel mechanisms to
 register <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files and device handlers. This is fine if you want to do something the
 kernel programmers thought you’d want, such as write a device driver. But what if
 you want to do something unusual, to change the behavior of the system in some
 way? Then, you are mostly on your own.
-</p><!-- l. 1172 --><p class='indent'>   If you are not being sensible and using a virtual machine then this is where kernel
+</p><!-- l. 1171 --><p class='indent'>   If you are not being sensible and using a virtual machine then this is where kernel
 programming can become hazardous. While writing the example below, I killed the
 <code> <span class='ectt-1000'>open()</span>
 </code> system call. This meant I could not open any files, I could not run any
 programs, and I could not shutdown the system. I had to restart the virtual
-machine. No important files got anihilated, but if I was doing this on some live
+machine. No important files got annihilated, but if I was doing this on some live
 mission critical system then that could have been a possible outcome. To
 ensure you do not lose any files, even within a test environment, please run
 <code> <span class='ectt-1000'>sync</span>
 </code> right before you do the <code>  <span class='ectt-1000'>insmod</span>
 </code> and the <code>  <span class='ectt-1000'>rmmod</span>
 </code>.
-</p><!-- l. 1179 --><p class='indent'>   Forget about <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files, forget about device files. They are just minor details.
+</p><!-- l. 1178 --><p class='indent'>   Forget about <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc</span></span></span> files, forget about device files. They are just minor details.
 Minutiae in the vast expanse of the universe. The real process to kernel
 communication mechanism, the one used by all processes, is <span class='ecti-1000'>system calls</span>. When a
 process requests a service from the kernel (such as opening a file, forking to a new
@@ -2875,11 +2875,11 @@ change the behaviour of the kernel in interesting ways, this is the place to do
 it. By the way, if you want to see which system calls a program uses, run
 <code> <span class='ectt-1000'>strace &lt;arguments&gt;</span>
 </code>.
-</p><!-- l. 1187 --><p class='indent'>   In general, a process is not supposed to be able to access the kernel. It can not
+</p><!-- l. 1186 --><p class='indent'>   In general, a process is not supposed to be able to access the kernel. It can not
 access kernel memory and it can’t call kernel functions. The hardware of the CPU
 enforces this (that is the reason why it is called “protected mode” or “page
 protection”).
-</p><!-- l. 1191 --><p class='indent'>   System calls are an exception to this general rule. What happens is that the
+</p><!-- l. 1190 --><p class='indent'>   System calls are an exception to this general rule. What happens is that the
 process fills the registers with the appropriate values and then calls a special
 instruction which jumps to a previously defined location in the kernel (of course, that
 location is readable by user processes, it is not writable by them). Under Intel CPUs,
@@ -2887,7 +2887,7 @@ this is done by means of interrupt 0x80. The hardware knows that once you jump t
 this location, you are no longer running in restricted user mode, but as the
 operating system kernel — and therefore you’re allowed to do whatever you
 want.
-</p><!-- l. 1196 --><p class='indent'>   The location in the kernel a process can jump to is called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>system_call</span></span></span>. The
+</p><!-- l. 1195 --><p class='indent'>   The location in the kernel a process can jump to is called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>system_call</span></span></span>. The
 procedure at that location checks the system call number, which tells the kernel what
 service the process requested. Then, it looks at the table of system calls
 (<code>  <span class='ectt-1000'>sys_call_table</span>
@@ -2900,7 +2900,7 @@ different process, if the process time ran out). If you want to read this code,
 at the source file <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>arch/$(architecture)/kernel/entry.S</span></span></span>, after the line
 <code> <span class='ectt-1000'>ENTRY(system_call)</span>
 </code>.
-</p><!-- l. 1202 --><p class='indent'>   So, if we want to change the way a certain system call works, what we need to do
+</p><!-- l. 1201 --><p class='indent'>   So, if we want to change the way a certain system call works, what we need to do
 is to write our own function to implement it (usually by adding a bit of our own
 code, and then calling the original function) and then change the pointer at
 <code> <span class='ectt-1000'>sys_call_table</span>
@@ -2908,7 +2908,7 @@ code, and then calling the original function) and then change the pointer at
 don’t want to leave the system in an unstable state, it’s important for
 <code> <span class='ectt-1000'>cleanup_module</span>
 </code> to restore the table to its original state.
-</p><!-- l. 1205 --><p class='indent'>   The source code here is an example of such a kernel module. We want to “spy” on a certain
+</p><!-- l. 1204 --><p class='indent'>   The source code here is an example of such a kernel module. We want to “spy” on a certain
 user, and to <code>  <span class='ectt-1000'>pr_info()</span>
 </code> a message whenever that user opens a file. Towards this end, we
 replace the system call to open a file with our own function, called
@@ -2918,7 +2918,7 @@ spy on, it calls <code>  <span class='ectt-1000'>pr_info()</span>
 </code> to display the name of the file to be opened. Then, either way, it calls the original
 <code> <span class='ectt-1000'>open()</span>
 </code> function with the same parameters, to actually open the file.
-</p><!-- l. 1211 --><p class='indent'>   The <code>  <span class='ectt-1000'>init_module</span>
+</p><!-- l. 1210 --><p class='indent'>   The <code>  <span class='ectt-1000'>init_module</span>
 </code> function replaces the appropriate location in
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> and keeps the original pointer in a variable. The
@@ -2936,7 +2936,7 @@ with <code>  <span class='ectt-1000'>B_open</span>
 </code>, which will call what it thinks is the original system call,
 <code> <span class='ectt-1000'>A_open</span>
 </code>, when it’s done.
-</p><!-- l. 1218 --><p class='indent'>   Now, if B is removed first, everything will be well — it will simply restore the system
+</p><!-- l. 1217 --><p class='indent'>   Now, if B is removed first, everything will be well — it will simply restore the system
 call to <code>  <span class='ectt-1000'>A_open</span>
 </code>, which calls the original. However, if A is removed and then B is removed, the
 system will crash. A’s removal will restore the system call to the original,
@@ -2959,7 +2959,7 @@ problem. When A is removed, it sees that the system call was changed to
 </code> will still try to call <code>  <span class='ectt-1000'>A_open</span>
 </code> which is no longer there, so that even without removing B the system would
 crash.
-</p><!-- l. 1226 --><p class='indent'>   Note that all the related problems make syscall stealing unfeasiable for
+</p><!-- l. 1225 --><p class='indent'>   Note that all the related problems make syscall stealing unfeasible for
 production use. In order to keep people from doing potential harmful things
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> is no longer exported. This means, if you want to do something more than a mere
@@ -2967,8 +2967,8 @@ dry run of this example, you will have to patch your current kernel in order to
 <code> <span class='ectt-1000'>sys_call_table</span>
 </code> exported. In the example directory you will find a README and the patch. As you
 can imagine, such modifications are not to be taken lightly. Do not try this on
-valueable systems (ie systems that you do not own - or cannot restore easily). You
+valuable systems (ie systems that you do not own - or cannot restore easily). You will
-will need to get the complete sourcecode of this guide as a tarball in order to get the
+need to get the complete sourcecode of this guide as a tarball in order to get the
 patch and the README. Depending on your kernel version, you might even need to
 hand apply the patch.
 </p><!-- l. 1 --><p class='indent'>
@@ -3110,13 +3110,13 @@ hand apply the patch.
 <a id='x1-40302r135'></a><span class='ecrm-0500'>135</span><span class='ectt-0800'>module_exit(syscall_end);</span> 
 <a id='x1-40304r136'></a><span class='ecrm-0500'>136</span> 
 <a id='x1-40306r137'></a><span class='ecrm-0500'>137</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1471'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1237 --><p class='noindent'>
+<!-- l. 1236 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='blocking-processes-and-threads'><span class='titlemark'>0.11   </span> <a id='x1-410000.11'></a>Blocking Processes and threads</h3>
-<!-- l. 1239 --><p class='noindent'>
+<!-- l. 1238 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='sleep'><span class='titlemark'>0.11.1   </span> <a id='x1-420000.11.1'></a>Sleep</h4>
-<!-- l. 1241 --><p class='noindent'>What do you do when somebody asks you for something you can not do right
+<!-- l. 1240 --><p class='noindent'>What do you do when somebody asks you for something you can not do right
 away? If you are a human being and you are bothered by a human being, the
 only thing you can say is: "<span class='ecti-1000'>Not right now, I’m busy. Go away!</span>". But if you
 are a kernel module and you are bothered by a process, you have another
@@ -3127,21 +3127,21 @@ processes are being put to sleep by the kernel and woken up all the time (that
                                                                   
 is the way multiple processes appear to run on the same time on a single
 CPU).
-</p><!-- l. 1247 --><p class='indent'>   This kernel module is an example of this. The file (called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/sleep</span></span></span>) can only
+</p><!-- l. 1246 --><p class='indent'>   This kernel module is an example of this. The file (called <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/sleep</span></span></span>) can only
 be opened by a single process at a time. If the file is already open, the kernel module
 calls <code>  <span class='ectt-1000'>wait_event_interruptible</span>
 </code>. The easiest way to keep a file open is to open it with:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb53'><a id='x1-42004r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>tail -f</span></pre>
-<!-- l. 1256 --><p class='indent'>   This function changes the status of the task (a task is the kernel data structure
+<!-- l. 1255 --><p class='indent'>   This function changes the status of the task (a task is the kernel data structure
 which holds information about a process and the system call it is in, if any) to
 <code> <span class='ectt-1000'>TASK_INTERRUPTIBLE</span>
 </code>, which means that the task will not run until it is woken up somehow, and adds it to
 WaitQ, the queue of tasks waiting to access the file. Then, the function calls the
 scheduler to context switch to a different process, one which has some use for the
 CPU.
-</p><!-- l. 1260 --><p class='indent'>   When a process is done with the file, it closes it, and
+</p><!-- l. 1259 --><p class='indent'>   When a process is done with the file, it closes it, and
 <code> <span class='ectt-1000'>module_close</span>
 </code> is called. That function wakes up all the processes in the queue (there’s no
 mechanism to only wake up one of them). It then returns and the process which just
@@ -3151,20 +3151,20 @@ Eventually, one of the processes which was in the queue will be given control
 of the CPU by the scheduler. It starts at the point right after the call to
 <code> <span class='ectt-1000'>module_interruptible_sleep_on</span>
 </code>.
-</p><!-- l. 1267 --><p class='indent'>   This means that the process is still in kernel mode - as far as the process
+</p><!-- l. 1266 --><p class='indent'>   This means that the process is still in kernel mode - as far as the process
 is concerned, it issued the open system call and the system call has not
 returned yet. The process does not know somebody else used the CPU for
 most of the time between the moment it issued the call and the moment it
 returned.
-</p><!-- l. 1270 --><p class='indent'>   It can then proceed to set a global variable to tell all the other processes that the
+</p><!-- l. 1269 --><p class='indent'>   It can then proceed to set a global variable to tell all the other processes that the
 file is still open and go on with its life. When the other processes get a piece of the
 CPU, they’ll see that global variable and go back to sleep.
-</p><!-- l. 1273 --><p class='indent'>   So we will use <code>  <span class='ectt-1000'>tail -f</span>
+</p><!-- l. 1272 --><p class='indent'>   So we will use <code>  <span class='ectt-1000'>tail -f</span>
 </code> to keep the file open in the background, while trying to access it with another
 process (again in the background, so that we need not switch to a different vt). As
 soon as the first background process is killed with kill %1 , the second is woken up, is
 able to access the file and finally terminates.
-</p><!-- l. 1276 --><p class='indent'>   To make our life more interesting, <code>  <span class='ectt-1000'>module_close</span>
+</p><!-- l. 1275 --><p class='indent'>   To make our life more interesting, <code>  <span class='ectt-1000'>module_close</span>
 </code> does not have a monopoly on waking up the processes which wait to access the file.
 A signal, such as <span class='ecti-1000'>Ctrl +c </span>(<span class='ecbx-1000'>SIGINT</span>) can also wake up a process. This is because we
 used <code>  <span class='ectt-1000'>module_interruptible_sleep_on</span>
@@ -3174,11 +3174,11 @@ used <code>  <span class='ectt-1000'>module_interruptible_sleep_on</span>
                                                                   
 </code> instead, but that would have resulted in extremely angry users whose <span class='ecti-1000'>Ctrl+c</span>’s are
 ignored.
-</p><!-- l. 1280 --><p class='indent'>   In that case, we want to return with
+</p><!-- l. 1279 --><p class='indent'>   In that case, we want to return with
 <code> <span class='ectt-1000'>-EINTR</span>
 </code> immediately. This is important so users can, for example, kill the process before it
 receives the file.
-</p><!-- l. 1282 --><p class='indent'>   There is one more point to remember. Some times processes don’t want to sleep, they want
+</p><!-- l. 1281 --><p class='indent'>   There is one more point to remember. Some times processes don’t want to sleep, they want
 either to get what they want immediately, or to be told it cannot be done. Such processes
 use the <code>  <span class='ectt-1000'>O_NONBLOCK</span>
 </code> flag when opening the file. The kernel is supposed to respond by returning with the error
@@ -3214,7 +3214,7 @@ $ cat_nonblock /proc/sleep
 Last input:
 $
 </pre>
-<!-- l. 1307 --><p class='nopar'>
+<!-- l. 1306 --><p class='nopar'>
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb54'><a id='x1-42018r1'></a><span class='ecrm-0500'>1</span><span id='textcolor1472'><span class='ectt-0800'>/*</span></span> 
@@ -3498,14 +3498,14 @@ $
 <a id='x1-42568r57'></a><span class='ecrm-0500'>57</span> 
 <a id='x1-42570r58'></a><span class='ecrm-0500'>58</span><span class='ectt-0800'>    </span><span id='textcolor1709'><span class='ectt-0800'>return</span></span><span class='ectt-0800'> 0;</span> 
 <a id='x1-42572r59'></a><span class='ecrm-0500'>59</span><span class='ectt-0800'>}</span></pre>
-<!-- l. 1313 --><p class='noindent'>
+<!-- l. 1312 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='completions'><span class='titlemark'>0.11.2   </span> <a id='x1-430000.11.2'></a>Completions</h4>
-<!-- l. 1315 --><p class='noindent'>Sometimes one thing should happen before another within a module having multiple threads.
+<!-- l. 1314 --><p class='noindent'>Sometimes one thing should happen before another within a module having multiple threads.
 Rather than using <code>  <span class='ectt-1000'>/bin/sleep</span>
 </code> commands, the kernel has another way to do this which allows timeouts or
 interrupts to also happen.
-</p><!-- l. 1318 --><p class='indent'>   In the following example two threads are started, but one needs to start before
+</p><!-- l. 1317 --><p class='indent'>   In the following example two threads are started, but one needs to start before
 another.
 </p><!-- l. 1 --><p class='indent'>
                                                                   
@@ -3588,31 +3588,31 @@ another.
 <a id='x1-43149r74'></a><span class='ecrm-0500'>74</span> 
 <a id='x1-43151r75'></a><span class='ecrm-0500'>75</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1760'><span class='ectt-0800'>"Completions example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-43153r76'></a><span class='ecrm-0500'>76</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1761'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1322 --><p class='indent'>   The <code>  <span class='ectt-1000'>machine</span>
+<!-- l. 1321 --><p class='indent'>   The <code>  <span class='ectt-1000'>machine</span>
 </code> structure stores the completion states for the two threads. At the exit
 point of each thread the respective completion state is updated, and
 <code> <span class='ectt-1000'>wait_for_completion</span>
 </code> is used by the flywheel thread to ensure that it does not begin prematurely.
-</p><!-- l. 1325 --><p class='indent'>   So even though <code>  <span class='ectt-1000'>flywheel_thread</span>
+</p><!-- l. 1324 --><p class='indent'>   So even though <code>  <span class='ectt-1000'>flywheel_thread</span>
 </code> is started first you should notice if you load this module and run
 <code> <span class='ectt-1000'>dmesg</span>
 </code> that turning the crank always happens first because the flywheel thread waits for it
 to complete.
-</p><!-- l. 1327 --><p class='indent'>   There are other variations upon the
+</p><!-- l. 1326 --><p class='indent'>   There are other variations upon the
 <code> <span class='ectt-1000'>wait_for_completion</span>
 </code> function, which include timeouts or being interrupted, but this basic mechanism is
 enough for many common situations without adding a lot of complexity.
-</p><!-- l. 1329 --><p class='noindent'>
+</p><!-- l. 1328 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='avoiding-collisions-and-deadlocks'><span class='titlemark'>0.12   </span> <a id='x1-440000.12'></a>Avoiding Collisions and Deadlocks</h3>
-<!-- l. 1331 --><p class='noindent'>If processes running on different CPUs or in different threads try to access the same
+<!-- l. 1330 --><p class='noindent'>If processes running on different CPUs or in different threads try to access the same
 memory, then it is possible that strange things can happen or your system can lock
 up. To avoid this, various types of mutual exclusion kernel functions are available.
 These indicate if a section of code is "locked" or "unlocked" so that simultaneous
 attempts to run it can not happen.
 </p>
    <h4 class='subsectionHead' id='mutex'><span class='titlemark'>0.12.1   </span> <a id='x1-450000.12.1'></a>Mutex</h4>
-<!-- l. 1336 --><p class='noindent'>You can use kernel mutexes (mutual exclusions) in much the same manner that you
+<!-- l. 1335 --><p class='noindent'>You can use kernel mutexes (mutual exclusions) in much the same manner that you
 might deploy them in userland. This may be all that is needed to avoid collisions in
 most cases.
 </p><!-- l. 1 --><p class='indent'>
@@ -3658,18 +3658,18 @@ most cases.
 <a id='x1-45078r39'></a><span class='ecrm-0500'>39</span> 
 <a id='x1-45080r40'></a><span class='ecrm-0500'>40</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1802'><span class='ectt-0800'>"Mutex example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-45082r41'></a><span class='ecrm-0500'>41</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1803'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1341 --><p class='noindent'>
+<!-- l. 1340 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='spinlocks'><span class='titlemark'>0.12.2   </span> <a id='x1-460000.12.2'></a>Spinlocks</h4>
-<!-- l. 1343 --><p class='noindent'>As the name suggests, spinlocks lock up the CPU that the code is running on,
+<!-- l. 1342 --><p class='noindent'>As the name suggests, spinlocks lock up the CPU that the code is running on,
 taking 100% of its resources. Because of this you should only use the spinlock
                                                                   
 
                                                                   
 mechanism around code which is likely to take no more than a few milliseconds to
-run and so will not noticably slow anything down from the user’s point of
+run and so will not noticeably slow anything down from the user’s point of
 view.
-</p><!-- l. 1346 --><p class='indent'>   The example here is <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>"irq safe"</span></span></span> in that if interrupts happen during the lock then
+</p><!-- l. 1345 --><p class='indent'>   The example here is <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>"irq safe"</span></span></span> in that if interrupts happen during the lock then
 they will not be forgotten and will activate when the unlock happens, using the
 <code> <span class='ectt-1000'>flags</span>
 </code> variable to retain their state.
@@ -3738,10 +3738,10 @@ they will not be forgotten and will activate when the unlock happens, using the
 <a id='x1-46123r61'></a><span class='ecrm-0500'>61</span> 
 <a id='x1-46125r62'></a><span class='ecrm-0500'>62</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1858'><span class='ectt-0800'>"Spinlock example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-46127r63'></a><span class='ecrm-0500'>63</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1859'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1350 --><p class='noindent'>
+<!-- l. 1349 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='read-and-write-locks'><span class='titlemark'>0.12.3   </span> <a id='x1-470000.12.3'></a>Read and write locks</h4>
-<!-- l. 1352 --><p class='noindent'>Read and write locks are specialised kinds of spinlocks so that you can exclusively
+<!-- l. 1351 --><p class='noindent'>Read and write locks are specialised kinds of spinlocks so that you can exclusively
 read from something or write to something. Like the earlier spinlocks example, the
 one below shows an "irq safe" situation in which if other functions were triggered
 from irqs which might also read and write to whatever you are concerned with
@@ -3806,14 +3806,14 @@ module.
 <a id='x1-47106r53'></a><span class='ecrm-0500'>53</span> 
 <a id='x1-47108r54'></a><span class='ecrm-0500'>54</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor1906'><span class='ectt-0800'>"Read/Write locks example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-47110r55'></a><span class='ecrm-0500'>55</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor1907'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1358 --><p class='indent'>   Of course, if you know for sure that there are no functions triggered by irqs
+<!-- l. 1357 --><p class='indent'>   Of course, if you know for sure that there are no functions triggered by irqs
 which could possibly interfere with your logic then you can use the simpler
 <code> <span class='ectt-1000'>read_lock(&amp;myrwlock)</span>
 </code> and <code>  <span class='ectt-1000'>read_unlock(&amp;myrwlock)</span>
 </code> or the corresponding write functions.
 </p>
    <h4 class='subsectionHead' id='atomic-operations'><span class='titlemark'>0.12.4   </span> <a id='x1-480000.12.4'></a>Atomic operations</h4>
-<!-- l. 1361 --><p class='noindent'>If you are doing simple arithmetic: adding, subtracting or bitwise operations, then
+<!-- l. 1360 --><p class='noindent'>If you are doing simple arithmetic: adding, subtracting or bitwise operations, then
 there is another way in the multi-CPU and multi-hyperthreaded world to stop other
 parts of the system from messing with your mojo. By using atomic operations you
 can be confident that your addition, subtraction or bit flip did actually happen
@@ -3898,21 +3898,21 @@ below.
                                                                   
 
                                                                   
-<!-- l. 1368 --><p class='noindent'>
+<!-- l. 1367 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='replacing-print-macros'><span class='titlemark'>0.13   </span> <a id='x1-490000.13'></a>Replacing Print Macros</h3>
-<!-- l. 1370 --><p class='noindent'>
+<!-- l. 1369 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='replacement'><span class='titlemark'>0.13.1   </span> <a id='x1-500000.13.1'></a>Replacement</h4>
-<!-- l. 1372 --><p class='noindent'>In Section <a href='#x1-80042'>2<!-- tex4ht:ref: sec:using_x  --></a>, I said that X Window System and kernel module programming do not
+<!-- l. 1371 --><p class='noindent'>In Section <a href='#x1-80042'>2<!-- tex4ht:ref: sec:using_x  --></a>, I said that X Window System and kernel module programming do not
 mix. That is true for developing kernel modules. But in actual use, you want to be
 able to send messages to whichever tty the command to load the module came
 from.
-</p><!-- l. 1376 --><p class='indent'>   "tty" is an abbreviation of <span class='ecti-1000'>teletype</span>: originally a combination keyboard-printer
+</p><!-- l. 1375 --><p class='indent'>   "tty" is an abbreviation of <span class='ecti-1000'>teletype</span>: originally a combination keyboard-printer
 used to communicate with a Unix system, and today an abstraction for the text
 stream used for a Unix program, whether it is a physical terminal, an xterm on an X
 display, a network connection used with ssh, etc.
-</p><!-- l. 1378 --><p class='indent'>   The way this is done is by using current, a pointer to the currently running task,
+</p><!-- l. 1377 --><p class='indent'>   The way this is done is by using current, a pointer to the currently running task,
 to get the current task’s tty structure. Then, we look inside that tty structure to find
 a pointer to a string write function, which we use to write a string to the
 tty.
@@ -3995,16 +3995,16 @@ tty.
 <a id='x1-50150r75'></a><span class='ecrm-0500'>75</span><span class='ectt-0800'>module_exit(print_string_exit);</span> 
 <a id='x1-50152r76'></a><span class='ecrm-0500'>76</span> 
 <a id='x1-50154r77'></a><span class='ecrm-0500'>77</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2032'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1383 --><p class='noindent'>
+<!-- l. 1382 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='flashing-keyboard-leds'><span class='titlemark'>0.13.2   </span> <a id='x1-510000.13.2'></a>Flashing keyboard LEDs</h4>
-<!-- l. 1385 --><p class='noindent'>In certain conditions, you may desire a simpler and more direct way to communicate
+<!-- l. 1384 --><p class='noindent'>In certain conditions, you may desire a simpler and more direct way to communicate
 to the external world. Flashing keyboard LEDs can be such a solution: It is an
 immediate way to attract attention or to display a status condition. Keyboard LEDs
 are present on every hardware, they are always visible, they do not need any setup,
 and their use is rather simple and non-intrusive, compared to writing to a tty or a
 file.
-</p><!-- l. 1389 --><p class='indent'>   The following source code illustrates a minimal kernel module which, when
+</p><!-- l. 1388 --><p class='indent'>   The following source code illustrates a minimal kernel module which, when
 loaded, starts blinking the keyboard LEDs until it is unloaded.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4100,7 +4100,7 @@ loaded, starts blinking the keyboard LEDs until it is unloaded.
                                                                   
 
                                                                   
-<!-- l. 1393 --><p class='indent'>   If none of the examples in this chapter fit your debugging needs,
+<!-- l. 1392 --><p class='indent'>   If none of the examples in this chapter fit your debugging needs,
 there might yet be some other tricks to try. Ever wondered what
 <code> <span class='ectt-1000'>CONFIG_LL_DEBUG</span>
 </code> in <code>  <span class='ectt-1000'>make menuconfig</span>
@@ -4111,22 +4111,22 @@ everything what your code does over a serial line. If you find yourself porting
 kernel to some new and former unsupported architecture, this is usually amongst the
 first things that should be implemented. Logging over a netconsole might also be
 worth a try.
-</p><!-- l. 1400 --><p class='indent'>   While you have seen lots of stuff that can be used to aid debugging here, there are
+</p><!-- l. 1399 --><p class='indent'>   While you have seen lots of stuff that can be used to aid debugging here, there are
 some things to be aware of. Debugging is almost always intrusive. Adding debug code
 can change the situation enough to make the bug seem to dissappear. Thus you
 should try to keep debug code to a minimum and make sure it does not show up in
 production code.
-</p><!-- l. 1404 --><p class='noindent'>
+</p><!-- l. 1403 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='scheduling-tasks'><span class='titlemark'>0.14   </span> <a id='x1-520000.14'></a>Scheduling Tasks</h3>
-<!-- l. 1406 --><p class='noindent'>There are two main ways of running tasks: tasklets and work queues. Tasklets are a
+<!-- l. 1405 --><p class='noindent'>There are two main ways of running tasks: tasklets and work queues. Tasklets are a
 quick and easy way of scheduling a single function to be run. For example, when
 triggered from an interrupt, whereas work queues are more complicated but also
 better suited to running multiple things in a sequence.
-</p><!-- l. 1410 --><p class='noindent'>
+</p><!-- l. 1409 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='tasklets'><span class='titlemark'>0.14.1   </span> <a id='x1-530000.14.1'></a>Tasklets</h4>
-<!-- l. 1412 --><p class='noindent'>Here is an example tasklet module. The
+<!-- l. 1411 --><p class='noindent'>Here is an example tasklet module. The
 <code> <span class='ectt-1000'>tasklet_fn</span>
 </code> function runs for a few seconds and in the mean time execution of the
 <code> <span class='ectt-1000'>example_tasklet_init</span>
@@ -4170,7 +4170,7 @@ better suited to running multiple things in a sequence.
 <a id='x1-53072r35'></a><span class='ecrm-0500'>35</span> 
 <a id='x1-53074r36'></a><span class='ecrm-0500'>36</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2152'><span class='ectt-0800'>"Tasklet example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-53076r37'></a><span class='ecrm-0500'>37</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2153'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1417 --><p class='indent'>   So with this example loaded <code>  <span class='ectt-1000'>dmesg</span>
+<!-- l. 1416 --><p class='indent'>   So with this example loaded <code>  <span class='ectt-1000'>dmesg</span>
 </code> should show:
                                                                   
 
@@ -4182,11 +4182,11 @@ Example tasklet starts
 Example tasklet init continues...
 Example tasklet ends
 </pre>
-<!-- l. 1424 --><p class='nopar'>
+<!-- l. 1423 --><p class='nopar'>
-</p><!-- l. 1426 --><p class='noindent'>
+</p><!-- l. 1425 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='work-queues'><span class='titlemark'>0.14.2   </span> <a id='x1-540000.14.2'></a>Work queues</h4>
-<!-- l. 1428 --><p class='noindent'>To add a task to the scheduler we can use a workqueue. The kernel then uses the
+<!-- l. 1427 --><p class='noindent'>To add a task to the scheduler we can use a workqueue. The kernel then uses the
 Completely Fair Scheduler (CFS) to execute work within the queue.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4224,19 +4224,19 @@ Completely Fair Scheduler (CFS) to execute work within the queue.
 <a id='x1-54064r32'></a><span class='ecrm-0500'>32</span> 
 <a id='x1-54066r33'></a><span class='ecrm-0500'>33</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2181'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-54068r34'></a><span class='ecrm-0500'>34</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2182'><span class='ectt-0800'>"Workqueue example"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1433 --><p class='noindent'>
+<!-- l. 1432 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='interrupt-handlers'><span class='titlemark'>0.15   </span> <a id='x1-550000.15'></a>Interrupt Handlers</h3>
-<!-- l. 1435 --><p class='noindent'>
+<!-- l. 1434 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='interrupt-handlers1'><span class='titlemark'>0.15.1   </span> <a id='x1-560000.15.1'></a>Interrupt Handlers</h4>
-<!-- l. 1437 --><p class='noindent'>Except for the last chapter, everything we did in the kernel so far we have done as a
+<!-- l. 1436 --><p class='noindent'>Except for the last chapter, everything we did in the kernel so far we have done as a
 response to a process asking for it, either by dealing with a special file, sending an
 <code> <span class='ectt-1000'>ioctl()</span>
 </code>, or issuing a system call. But the job of the kernel is not just to respond to process
 requests. Another job, which is every bit as important, is to speak to the hardware
 connected to the machine.
-</p><!-- l. 1441 --><p class='indent'>   There are two types of interaction between the CPU and the rest of the
+</p><!-- l. 1440 --><p class='indent'>   There are two types of interaction between the CPU and the rest of the
 computer’s hardware. The first type is when the CPU gives orders to the hardware,
 the order is when the hardware needs to tell the CPU something. The second, called
 interrupts, is much harder to implement because it has to be dealt with when
@@ -4246,14 +4246,14 @@ lost.
                                                                   
 
                                                                   
-</p><!-- l. 1446 --><p class='indent'>   Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
+</p><!-- l. 1445 --><p class='indent'>   Under Linux, hardware interrupts are called IRQ’s (Interrupt ReQuests). There
 are two types of IRQ’s, short and long. A short IRQ is one which is expected to take
 a very short period of time, during which the rest of the machine will be blocked and
 no other interrupts will be handled. A long IRQ is one which can take longer, and
 during which other interrupts may occur (but not interrupts from the same
 device). If at all possible, it is better to declare an interrupt handler to be
 long.
-</p><!-- l. 1452 --><p class='indent'>   When the CPU receives an interrupt, it stops whatever it is doing (unless it is
+</p><!-- l. 1451 --><p class='indent'>   When the CPU receives an interrupt, it stops whatever it is doing (unless it is
 processing a more important interrupt, in which case it will deal with this one
 only when the more important one is done), saves certain parameters on
 the stack and calls the interrupt handler. This means that certain things
@@ -4265,10 +4265,10 @@ the new information at a later time (this is called the "bottom half") and
 return. The kernel is then guaranteed to call the bottom half as soon as
 possible – and when it does, everything allowed in kernel modules will be
 allowed.
-</p><!-- l. 1458 --><p class='indent'>   The way to implement this is to call
+</p><!-- l. 1457 --><p class='indent'>   The way to implement this is to call
 <code> <span class='ectt-1000'>request_irq()</span>
 </code> to get your interrupt handler called when the relevant IRQ is received.
-</p><!-- l. 1460 --><p class='indent'>   In practice IRQ handling can be a bit more complex. Hardware is often
+</p><!-- l. 1459 --><p class='indent'>   In practice IRQ handling can be a bit more complex. Hardware is often
 designed in a way that chains two interrupt controllers, so that all the IRQs
 from interrupt controller B are cascaded to a certain IRQ from interrupt
 controller A. Of course, that requires that the kernel finds out which IRQ it
@@ -4278,11 +4278,11 @@ them requires handlers to be written in assembler, so they do not really
 fit into the kernel. They can be made to work similar to the others, but
 after that procedure, they are no longer any faster than "common" IRQs.
 SMP enabled kernels running on systems with more than one processor
-need to solve another truckload of problems. It is not enough to know if
+need to solve another truckload of problems. It is not enough to know if a
-a certain IRQs has happend, it’s also important for what CPU(s) it was
+certain IRQs has happened, it’s also important to know what CPU(s) it was
 for. People still interested in more details, might want to refer to "APIC"
 now.
-</p><!-- l. 1469 --><p class='indent'>   This function receives the IRQ number, the name of the function,
+</p><!-- l. 1468 --><p class='indent'>   This function receives the IRQ number, the name of the function,
 flags, a name for <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/interrupts</span></span></span> and a parameter to be passed to the
 interrupt handler. Usually there is a certain number of IRQs available.
 How many IRQs there are is hardware-dependent. The flags can include
@@ -4295,16 +4295,16 @@ already a handler on this IRQ, or if you are both willing to share.
                                                                   
 
                                                                   
-</p><!-- l. 1475 --><p class='noindent'>
+</p><!-- l. 1474 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='detecting-button-presses'><span class='titlemark'>0.15.2   </span> <a id='x1-570000.15.2'></a>Detecting button presses</h4>
-<!-- l. 1477 --><p class='noindent'>Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
+<!-- l. 1476 --><p class='noindent'>Many popular single board computers, such as Raspberry Pi or Beagleboards, have a
 bunch of GPIO pins. Attaching buttons to those and then having a button press do
 something is a classic case in which you might need to use interrupts, so that instead
 of having the CPU waste time and battery power polling for a change in input state,
 it is better for the input to trigger the CPU to then run a particular handling
 function.
-</p><!-- l. 1481 --><p class='indent'>   Here is an example where buttons are connected to GPIO numbers 17 and 18 and
+</p><!-- l. 1480 --><p class='indent'>   Here is an example where buttons are connected to GPIO numbers 17 and 18 and
 an LED is connected to GPIO 4. You can change those numbers to whatever is
 appropriate for your board.
 </p><!-- l. 1 --><p class='indent'>
@@ -4454,14 +4454,14 @@ appropriate for your board.
 <a id='x1-57286r143'></a><span class='ecrm-0500'>143</span> 
 <a id='x1-57288r144'></a><span class='ecrm-0500'>144</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2289'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-57290r145'></a><span class='ecrm-0500'>145</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2290'><span class='ectt-0800'>"Handle some GPIO interrupts"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1486 --><p class='noindent'>
+<!-- l. 1485 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='bottom-half'><span class='titlemark'>0.15.3   </span> <a id='x1-580000.15.3'></a>Bottom Half</h4>
-<!-- l. 1488 --><p class='noindent'>Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
+<!-- l. 1487 --><p class='noindent'>Suppose you want to do a bunch of stuff inside of an interrupt routine. A common
 way to do that without rendering the interrupt unavailable for a significant duration
 is to combine it with a tasklet. This pushes the bulk of the work off into the
 scheduler.
-</p><!-- l. 1492 --><p class='indent'>   The example below modifies the previous example to also run an additional task
+</p><!-- l. 1491 --><p class='indent'>   The example below modifies the previous example to also run an additional task
 when an interrupt is triggered.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4626,10 +4626,10 @@ when an interrupt is triggered.
 <a id='x1-58318r159'></a><span class='ecrm-0500'>159</span> 
 <a id='x1-58320r160'></a><span class='ecrm-0500'>160</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2411'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-58322r161'></a><span class='ecrm-0500'>161</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2412'><span class='ectt-0800'>"Interrupt with top and bottom half"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1496 --><p class='noindent'>
+<!-- l. 1495 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='crypto'><span class='titlemark'>0.16   </span> <a id='x1-590000.16'></a>Crypto</h3>
-<!-- l. 1498 --><p class='noindent'>At the dawn of the internet, everybody trusted everybody completely…but that did
+<!-- l. 1497 --><p class='noindent'>At the dawn of the internet, everybody trusted everybody completely…but that did
 not work out so well. When this guide was originally written, it was a more innocent
 era in which almost nobody actually gave a damn about crypto - least of all kernel
 developers. That is certainly no longer the case now. To handle crypto stuff, the
@@ -4638,10 +4638,10 @@ favourite hash functions.
                                                                   
 
                                                                   
-</p><!-- l. 1503 --><p class='noindent'>
+</p><!-- l. 1502 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='hash-functions'><span class='titlemark'>0.16.1   </span> <a id='x1-600000.16.1'></a>Hash functions</h4>
-<!-- l. 1506 --><p class='noindent'>Calculating and checking the hashes of things is a common operation. Here is a
+<!-- l. 1505 --><p class='noindent'>Calculating and checking the hashes of things is a common operation. Here is a
 demonstration of how to calculate a sha256 hash within a kernel module.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4707,21 +4707,21 @@ demonstration of how to calculate a sha256 hash within a kernel module.
 <a id='x1-60120r60'></a><span class='ecrm-0500'>60</span> 
 <a id='x1-60122r61'></a><span class='ecrm-0500'>61</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2462'><span class='ectt-0800'>"sha256 hash test"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-60124r62'></a><span class='ecrm-0500'>62</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2463'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1511 --><p class='indent'>   Make and install the module:
+<!-- l. 1510 --><p class='indent'>   Make and install the module:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb68'><a id='x1-60129r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>make</span> 
 <a id='x1-60131r2'></a><span class='ecrm-0500'>2</span><span class='ectt-1000'>sudo insmod cryptosha256.ko</span> 
 <a id='x1-60133r3'></a><span class='ecrm-0500'>3</span><span class='ectt-1000'>dmesg</span></pre>
-<!-- l. 1519 --><p class='indent'>   And you should see that the hash was calculated for the test string.
+<!-- l. 1518 --><p class='indent'>   And you should see that the hash was calculated for the test string.
-</p><!-- l. 1521 --><p class='indent'>   Finally, remove the test module:
+</p><!-- l. 1520 --><p class='indent'>   Finally, remove the test module:
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb69'><a id='x1-60136r1'></a><span class='ecrm-0500'>1</span><span class='ectt-1000'>sudo rmmod cryptosha256</span></pre>
-<!-- l. 1527 --><p class='noindent'>
+<!-- l. 1526 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='symmetric-key-encryption'><span class='titlemark'>0.16.2   </span> <a id='x1-610000.16.2'></a>Symmetric key encryption</h4>
-<!-- l. 1529 --><p class='noindent'>Here is an example of symmetrically encrypting a string using the AES algorithm
+<!-- l. 1528 --><p class='noindent'>Here is an example of symmetrically encrypting a string using the AES algorithm
 and a password.
 </p><!-- l. 1 --><p class='indent'>
 </p>
@@ -4922,13 +4922,13 @@ and a password.
 <a id='x1-61390r195'></a><span class='ecrm-0500'>195</span> 
 <a id='x1-61392r196'></a><span class='ecrm-0500'>196</span><span class='ectt-0800'>MODULE_DESCRIPTION(</span><span id='textcolor2609'><span class='ectt-0800'>"Symmetric key encryption example"</span></span><span class='ectt-0800'>);</span> 
 <a id='x1-61394r197'></a><span class='ecrm-0500'>197</span><span class='ectt-0800'>MODULE_LICENSE(</span><span id='textcolor2610'><span class='ectt-0800'>"GPL"</span></span><span class='ectt-0800'>);</span></pre>
-<!-- l. 1533 --><p class='noindent'>
+<!-- l. 1532 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='standardizing-the-interfaces-the-device-model'><span class='titlemark'>0.17   </span> <a id='x1-620000.17'></a>Standardizing the interfaces: The Device Model</h3>
-<!-- l. 1535 --><p class='noindent'>Up to this point we have seen all kinds of modules doing all kinds of things, but there
+<!-- l. 1534 --><p class='noindent'>Up to this point we have seen all kinds of modules doing all kinds of things, but there
 was no consistency in their interfaces with the rest of the kernel. To impose some
 consistency such that there is at minimum a standardized way to start, suspend and
-resume a device a device model was added. An example is show below, and you can
+resume a device a device model was added. An example is shown below, and you can
 use this as a template to add your own suspend, resume or other interface
 functions.
 </p><!-- l. 1 --><p class='indent'>
@@ -5035,24 +5035,23 @@ functions.
                                                                   
 
                                                                   
-<!-- l. 1541 --><p class='noindent'>
+<!-- l. 1540 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='optimizations'><span class='titlemark'>0.18   </span> <a id='x1-630000.18'></a>Optimizations</h3>
-<!-- l. 1543 --><p class='noindent'>
+<!-- l. 1542 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='likely-and-unlikely-conditions'><span class='titlemark'>0.18.1   </span> <a id='x1-640000.18.1'></a>Likely and Unlikely conditions</h4>
-<!-- l. 1545 --><p class='noindent'>Sometimes you might want your code to run as quickly as possible,
+<!-- l. 1544 --><p class='noindent'>Sometimes you might want your code to run as quickly as possible,
 especially if it is handling an interrupt or doing something which might
-cause noticible latency. If your code contains boolean conditions and if you
+cause noticeable latency. If your code contains boolean conditions and if
-know that the conditions are almost always likely to evaluate as either
+you know that the conditions are almost always likely to evaluate as either
 <code> <span class='ectt-1000'>true</span>
 </code> or <code>  <span class='ectt-1000'>false</span>
 </code>, then you can allow the compiler to optimize for this using the
 <code> <span class='ectt-1000'>likely</span>
 </code> and <code>  <span class='ectt-1000'>unlikely</span>
-</code> macros.
+</code> macros. For example, when allocating memory you are almost always expecting this
-</p><!-- l. 1549 --><p class='indent'>   For example, when allocating memory you are almost always expecting this to
+to succeed.
-succeed.
 </p><!-- l. 1 --><p class='indent'>
 </p>
    <pre class='fancyvrb' id='fancyvrb72'><a id='x1-64012r1'></a><span class='ecrm-0500'>1</span><span class='ectt-0800'>bvl = bvec_alloc(gfp_mask, nr_iovecs, &amp;idx);</span> 
@@ -5061,50 +5060,50 @@ succeed.
 <a id='x1-64018r4'></a><span class='ecrm-0500'>4</span><span class='ectt-0800'>    bio = NULL;</span> 
 <a id='x1-64020r5'></a><span class='ecrm-0500'>5</span><span class='ectt-0800'>    </span><span id='textcolor2688'><span class='ectt-0800'>goto</span></span><span class='ectt-0800'> out;</span> 
 <a id='x1-64022r6'></a><span class='ecrm-0500'>6</span><span class='ectt-0800'>}</span></pre>
-<!-- l. 1560 --><p class='indent'>   When the <code>  <span class='ectt-1000'>unlikely</span>
+<!-- l. 1558 --><p class='indent'>   When the <code>  <span class='ectt-1000'>unlikely</span>
 </code> macro is used, the compiler alters its machine instruction output, so that it
 continues along the false branch and only jumps if the condition is true. That
 avoids flushing the processor pipeline. The opposite happens if you use the
 <code> <span class='ectt-1000'>likely</span>
 </code> macro.
-</p><!-- l. 1564 --><p class='noindent'>
+</p><!-- l. 1562 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='common-pitfalls'><span class='titlemark'>0.19   </span> <a id='x1-650000.19'></a>Common Pitfalls</h3>
-<!-- l. 1567 --><p class='noindent'>
+<!-- l. 1565 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='using-standard-libraries'><span class='titlemark'>0.19.1   </span> <a id='x1-660000.19.1'></a>Using standard libraries</h4>
-<!-- l. 1569 --><p class='noindent'>You can not do that. In a kernel module, you can only use kernel functions which are
+<!-- l. 1567 --><p class='noindent'>You can not do that. In a kernel module, you can only use kernel functions which are
 the functions you can see in <span class='obeylines-h'><span class='verb'><span class='ectt-1000'>/proc/kallsyms</span></span></span>.
                                                                   
 
                                                                   
-</p><!-- l. 1572 --><p class='noindent'>
+</p><!-- l. 1570 --><p class='noindent'>
 </p>
    <h4 class='subsectionHead' id='disabling-interrupts'><span class='titlemark'>0.19.2   </span> <a id='x1-670000.19.2'></a>Disabling interrupts</h4>
-<!-- l. 1574 --><p class='noindent'>You might need to do this for a short time and that is OK, but if you do not enable
+<!-- l. 1572 --><p class='noindent'>You might need to do this for a short time and that is OK, but if you do not enable
 them afterwards, your system will be stuck and you will have to power it
 off.
-</p><!-- l. 1576 --><p class='noindent'>
+</p><!-- l. 1574 --><p class='noindent'>
 </p>
    <h3 class='sectionHead' id='where-to-go-from-here'><span class='titlemark'>0.20   </span> <a id='x1-680000.20'></a>Where To Go From Here?</h3>
-<!-- l. 1578 --><p class='noindent'>For people seriously interested in kernel programming, I recommend <a href='https://kernelnewbies.org'>kernelnewbies.org</a>
+<!-- l. 1576 --><p class='noindent'>For people seriously interested in kernel programming, I recommend <a href='https://kernelnewbies.org'>kernelnewbies.org</a>
 and the <a href='https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation'>Documentation</a> subdirectory within the kernel source code which is not
 always easy to understand but can be a starting point for further investigation. Also,
 as Linus Torvalds said, the best way to learn the kernel is to read the source code
 yourself.
-</p><!-- l. 1581 --><p class='indent'>   If you are interested in more examples of short kernel modules then searching on
+</p><!-- l. 1579 --><p class='indent'>   If you are interested in more examples of short kernel modules then searching on
 sites such as Github and Gitlab is a good way to start, although there is a lot of
 duplication of older LKMPG examples which may not compile with newer kernel
 versions. You will also be able to find examples of the use of kernel modules to attack
 or compromise systems or exfiltrate data and those can be useful for thinking about
 how to defend systems and learning about existing security mechanisms within the
 kernel.
-</p><!-- l. 1584 --><p class='indent'>   I hope I have helped you in your quest to become a better programmer, or at
+</p><!-- l. 1582 --><p class='indent'>   I hope I have helped you in your quest to become a better programmer, or at
 least to have fun through technology. And, if you do write useful kernel modules, I
 hope you publish them under the GPL, so I can use them too.
-</p><!-- l. 1587 --><p class='indent'>   If you would like to contribute to this guide or notice anything glaringly wrong,
+</p><!-- l. 1585 --><p class='indent'>   If you would like to contribute to this guide or notice anything glaringly wrong,
 please create an issue at <a class='url' href='https://github.com/sysprog21/lkmpg'><span class='ectt-1000'>https://github.com/sysprog21/lkmpg</span></a>.
-</p><!-- l. 1589 --><p class='indent'>   Happy hacking!
+</p><!-- l. 1587 --><p class='indent'>   Happy hacking!
 </p>
     
 </body>