This patch introduces static key technique and adds a kernel module
to demostrate how to use static key to optimize an almost unlikely
branch, the module can interact with userspace thru a character device.
Signed-off-by: Peter Lin <peterlin@qilai.dev>
Since the commit b8780c363d80 ("sched: remove sleep_on() and friends
"), the description about sleep_on is incorrect and the example code has
been fixed by replacing it with wait_event family. Let's also fix the
description to match the corrected code.
Since sys_open is deprecated and some architectures don't support it.
We switch the implementation to sys_openat.
Moreover, in some architectures like x86-64, the prototype of syscall,
for example, openat(), might have been changed to struct pt_regs [1]
but we cannot promise that so support the two types
(sys_openat and pt_regs).
Also, to prevent other untraced tasks print out the information, add
the uid checking in our_sys_openat().
[1] https://lore.kernel.org/lkml/20180405095307.3730-1-linux@dominikbrodowski.net/Close#159
It failed silently when crypto_alloc_tfm() failed, so add an error
message to inform the developer to enable sha256 algorithm support.
Signed-off-by: Yu Chien Peter Lin <peterlin.tw@pm.me>
Currently, the description of the proc_ops in the file operation section
will confuse the reader with registering the device. Add more hints to
avoid it.
Currently, in 13.2 Flashing keyboard LEDs, the description of the
control-flow integrity, "Furthermore, the function prototype with
unsigned long argument may be an obstacle to the control-flow integrity
.", will confuse the reader.
It may lead the reader to think about hardware-assisted CFI like Intel
CET uses the shadow stack attack for ROP (backward-edge protection). But
the description of CFI here talks about the function pointer checking
with the prototype (forward-edge protection).
So add more information to make it more clear.
Close#151
The description of the attribute was added in sysfs section and referenced in vinput section.
In vinput section, just described the class_attribute and some macros about sysfs class.
Add file name at vinput-related examples begin.
Previously ioctl.c is a userspace program for chardev2.c and chardev.h [1].
But now, this file is an independent kernel module, and the original code
disappear.
This patch adds back the original userspace code and renames it to
userspace_ioctl.c.
[1] https://tldp.org/LDP/lkmpg/2.4/html/x856.html
Instead of using the old register_chrdev / unregister_chrdev API,
cdev interface which is newer and would be better for new driver programmers
in most cases. This commit is trying to give the brief overview for
this different interface.
This script do mainly 2 things:
1.
Generate file `Contributors` with git log in following format:
Contributor's name,<1-st e-mail>[,<2nd e-mail>][,<3rd e-mail>]...
The 2-nd email and so on are based on file `.mailmap` in the root
directory of the repo.
Note that it will also append contributors in File `Include`; and
will NOT append contributors in File `Exclude`.
If there are new contributors, script will sort `Contributor` after
append new contributors into each file; Otherwise it do nothing.
2.
Generate contrib.tex based on `Contributors` into lib/contrib.tex in
following format:
[name], (reasonable width) % [1-st e-mail]
Which is inspired by The Not So Short Introduction to Latex 2e[1]
We need to maintain `.mailmap`, `Exclude` and `Include` manually.
All Chinese name should be converted into English/Pinyin in `.mailmap`,
otherwise we may need extra pkg for latex to parse Chinese characters.
[1] - https://tobi.oetiker.ch/lshort/lshort.pdfClose#68
The dmesg command allows you to review the messages that are stored in the
ring buffer. Some Linux distributions have strict requirements for
dmesg, and you need to use sudo to use dmesg.
Since Linux v3.14, the read, write and seek operations of "struct file" are
guaranteed for thread safety [1][2]. This patch added an explanation.
Here are the potential problems:
chardev.c:
- Move the "msg_ptr" pointer into the read function to remove unnecessary usage.
- List the clear states of "already_open" by using mnemonic enumeration.
chardev2.c:
- The "buffer" in the write function is user space data. It cannot use in the
kernel space.
- Reduce the redundant type transformation.
- List the states of "already_open". Same as chardev.c.
[1] https://lore.kernel.org/lkml/20140303210359.26624.qmail@science.horizon.com/T/#u
[2] 9c225f2655
Parameters are case-sensitive, so myintArray is different from myintarray, and people who are running the example with copy/paste will find it doesn't work as described in the text.
In file {chardev,chardev2,sleep}.c, the variable to determine
the exclusive access was of integer type, which led to race
condition.
This patch rewrote the above with atomic CAS respectively
to eliminate the race.
Close#93
