Энциклопедия разработчика модулей ядра Linux

Путем этого достичь: используя текущий указатель на задачу, выполняемую в настоящее время, получить ее структуру tty. Затем мы смотрим внутри этой структура tty, чтобы найти указатель на функцию, пишущую строку на tty. Ее мы и используем для вывода.

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);

 }

}