75 lines
2.8 KiB
C
75 lines
2.8 KiB
C
/*
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* print_string.c - Send output to the tty we're running on, regardless if
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* it is through X11, telnet, etc. We do this by printing the string to the
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* tty associated with the current task.
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*/
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/sched.h> /* For current */
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#include <linux/tty.h> /* For the tty declarations */
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static void print_string(char *str)
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{
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/* The tty for the current task */
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struct tty_struct *my_tty = get_current_tty();
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/* If my_tty is NULL, the current task has no tty you can print to (i.e.,
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* if it is a daemon). If so, there is nothing we can do.
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*/
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if (my_tty) {
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const struct tty_operations *ttyops = my_tty->driver->ops;
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/* my_tty->driver is a struct which holds the tty's functions,
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* one of which (write) is used to write strings to the tty.
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* It can be used to take a string either from the user's or
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* kernel's memory segment.
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*
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* The function's 1st parameter is the tty to write to, because the
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* same function would normally be used for all tty's of a certain
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* type.
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* The 2nd parameter is a pointer to a string.
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* The 3rd parameter is the length of the string.
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*
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* As you will see below, sometimes it's necessary to use
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* preprocessor stuff to create code that works for different
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* kernel versions. The (naive) approach we've taken here does not
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* scale well. The right way to deal with this is described in
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* section 2 of
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* linux/Documentation/SubmittingPatches
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*/
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(ttyops->write)(my_tty, /* The tty itself */
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str, /* String */
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strlen(str)); /* Length */
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/* ttys were originally hardware devices, which (usually) strictly
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* followed the ASCII standard. In ASCII, to move to a new line you
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* need two characters, a carriage return and a line feed. On Unix,
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* the ASCII line feed is used for both purposes - so we can not
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* just use \n, because it would not have a carriage return and the
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* next line will start at the column right after the line feed.
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*
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* This is why text files are different between Unix and MS Windows.
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* In CP/M and derivatives, like MS-DOS and MS Windows, the ASCII
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* standard was strictly adhered to, and therefore a newline requires
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* both a LF and a CR.
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*/
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(ttyops->write)(my_tty, "\015\012", 2);
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}
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}
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static int __init print_string_init(void)
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{
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print_string("The module has been inserted. Hello world!");
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return 0;
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}
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static void __exit print_string_exit(void)
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{
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print_string("The module has been removed. Farewell world!");
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}
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module_init(print_string_init);
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module_exit(print_string_exit);
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MODULE_LICENSE("GPL");
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