Энциклопедия разработчика модулей ядра Linux

Замена для printk

В начале (глава1), я сказал, что X и программирование модулей ядра не совместимы. Это истинно при разработке модуля, но в фактическом использовании, Вы должны быть способны послать сообщениям любому tty[10]. Это важно для идентификации ошибок после того, как модуль выпущен, потому что он будет использоваться через любой из терминалов.

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 - 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"); 

}