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Каталог документации / Раздел "Программирование в Linux" / Оглавление документа

     
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 ^9.1. 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   

/* 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 <linux/kernel.h>   /* We're doing kernel work */
#include <linux/module.h>   /* Specifically, a module */

/* Deal with CONFIG_MODVERSIONS */
#if CONFIG_MODVERSIONS==1
#define MODVERSIONS
#include <linux/modversions.h>
#endif

/* Necessary here */
#include <linux/sched.h>    /* For current */
#include <linux/tty.h>      /* 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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