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printk.c

/* printk.c - send textual output to the tty you're

* running on, regardless of whether it's passed

* through X11, telnet, etc.

*/

/* Copyright (C) 1998 by Ori Pomerantz */


/* The necessary header files */

/* Standard in kernel modules */

#include /* We're doing kernel work */

#include /* Specifically, a module */


/* Deal with CONFIG_MODVERSIONS */

#if CONFIG_MODVERSIONS==1

#define MODVERSIONS

#include

#endif


/* Necessary here */

#include /* For current */

#include /* For the tty declarations */


/* Print the string to the appropriate tty, the one

* the current task uses */

void print_string(char *str) {

struct tty_struct *my_tty;

/* The tty for the current task */

my_tty = current->tty;

/* If my_tty is NULL, it means that the current task

* has no tty you can print to (this is possible, for

* example, if it's a daemon). In this case, there's

* nothing we can do. */

if (my_tty != NULL) {

/* my_tty->driver is a struct which holds the tty's

* functions, one of which (write) is used to

* write strings to the tty. It can be used to take

* a string either from the user's memory segment

* or the kernel's memory segment.

*

* The function's first parameter is the tty to

* write to, because the same function would

* normally be used for all tty's of a certain type.

* The second parameter controls whether the

* function receives a string from kernel memory

* (false, 0) or from user memory (true, non zero).

* The third parameter is a pointer to a string,

* and the fourth parameter is the length of

* the string. */

(*(my_tty->driver).write)(

my_tty, /* The tty itself */

0, /* We don't take the string from user space */

str, /* String */

strlen(str)); /* Length */

/* ttys were originally hardware devices, which

* (usually) adhered strictly to the ASCII standard.

* According to ASCII, to move to a new line you

* need two characters, a carriage return and a

* line feed. In Unix, on the other hand, the

* ASCII line feed is used for both purposes - so

* we can't just use \n, because it wouldn't have

* a carriage return and the next line will

* start at the column right after the line feed.

*

* BTW, this is the reason why the text file

* is different between Unix and Windows.

* In CP/M and its derivatives, such as MS-DOS and

* Windows, the ASCII standard was strictly

* adhered to, and therefore a new line requires

* both a line feed and a carriage return. */

(*(my_tty->driver).write)(my_tty, 0, "\015\012", 2);

}

}


/* Module initialization and cleanup ****************** */


/* Initialize the module - register the proc file */

int init_module() {

print_string("Module Inserted");

return 0;

}


/* Cleanup - unregister our file from /proc */

void cleanup_module() {

print_string("Module Removed");

}


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