Энциклопедия разработчика модулей ядра Linux - [19]

. К сожалению, мы не имеем простой способ удалить задачу из списка задачи.

Так как cleanup_module не может вернуть код ошибки (она имеет тип возврата void), возникает решение не позволить возвращаться вообще. Вместо завершения модуля мы вызываем sleep_on или module_sleep_on[11] чтобы отправить в спячку сам rmmod. Перед этим мы сообщаем функции, вызываемой по прерыванию таймера, чтобы она убрала себя из списка, устанавливая глобальную переменную. На следующем прерывании таймера, процесс rmmod будет пробужден, когда наша функция больше не в очереди, и безопасно удалит модуль.

sched.c

/* sched.c - schedule a function to be called on
* every timer interrupt.
*/
/* 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 because we use the proc fs */
#include

/* We scheduale tasks here */
#include

/* We also need the ability to put ourselves to sleep
* and wake up later */
#include

/* In 2.2.3 /usr/include/linux/version.h includes a
* macro for this, but 2.0.35 doesn't - so I add it
* here if necessary. */
#ifndef KERNEL_VERSION
#define KERNEL_VERSION(a,b,c) ((a)*65536+(b)*256+(c))
#endif

/* The number of times the timer interrupt has been
* called so far */
static int TimerIntrpt = 0;

/* This is used by cleanup, to prevent the module from
* being unloaded while intrpt_routine is still in
* the task queue */
static struct wait_queue *WaitQ = NULL;
static void intrpt_routine(void *);

/* The task queue structure for this task, from tqueue.h */
static struct tq_struct Task = {
 NULL,   /* Next item in list - queue_task will do
         * this for us */
 0,      /* A flag meaning we haven't been inserted
         * into a task queue yet */
 intrpt_routine, /* The function to run */
 NULL    /* The void* parameter for that function */
};

/* This function will be called on every timer
* interrupt. Notice the void* pointer - task functions
* can be used for more than one purpose, each time
* getting a different parameter. */
static void intrpt_routine(void *irrelevant) {
 /* Increment the counter */
 TimerIntrpt++;
 /* If cleanup wants us to die */
 if (WaitQ != NULL) wake_up(&WaitQ);
 /* Now cleanup_module can return */
 else queue_task(&Task, &tq_timer);
 /* Put ourselves back in the task queue */
}

/* Put data into the proc fs file. */
int procfile_read(char *buffer, char **buffer_location, off_t offset, int buffer_length, int zero) {
 int len;  /* The number of bytes actually used */
 /* This is static so it will still be in memory
 * when we leave this function */
 static char my_buffer[80];
 static int count = 1;
 /* We give all of our information in one go, so if
 * the anybody asks us if we have more information
 * the answer should always be no. */
 if (offset > 0) return 0;
 /* Fill the buffer and get its length */
 len = sprintf(my_buffer, "Timer was called %d times so far\n", TimerIntrpt);
 count++;
 /* Tell the function which called us where the buffer is */
 *buffer_location = my_buffer;
 /* Return the length */
 return len;
}

struct proc_dir_entry Our_Proc_File = {
 0, /* Inode number - ignore, it will be filled by
     * proc_register_dynamic */
 5, /* Length of the file name */
 "sched", /* The file name */
 S_IFREG | S_IRUGO,
 /* File mode - this is a regular file which can
  * be read by its owner, its group, and everybody else */
 1,  /* Number of links (directories where
      * the file is referenced) */
 0, 0,  /* The uid and gid for the file - we give it to root */
 80, /* The size of the file reported by ls. */
 NULL, /* functions which can be done on the
        * inode (linking, removing, etc.) - we don't
        * support any. */
 procfile_read,
 /* The read function for this file, the function called
  * when somebody tries to read something from it. */
 NULL
 /* We could have here a function to fill the
  * file's inode, to enable us to play with
  * permissions, ownership, etc. */
};

/* Initialize the module - register the proc file */
int init_module() {
 /* Put the task in the tq_timer task queue, so it
 * will be executed at next timer interrupt */
 queue_task(&Task, &tq_timer);
 /* Success if proc_register_dynamic is a success,
 * failure otherwise */
#if LINUX_VERSION_CODE > KERNEL_VERSION(2,2,0)
 return proc_register(&proc_root, &Our_Proc_File);
#else
 return proc_register_dynamic(&proc_root, &Our_Proc_File);
#endif
}

/* Cleanup */
void cleanup_module() {
 /* Unregister our /proc file */
 proc_unregister(&proc_root, Our_Proc_File.low_ino);
 /* Sleep until intrpt_routine is called one last
 * time. This is necessary, because otherwise we'll
 * deallocate the memory holding intrpt_routine and
 * Task while tq_timer still references them.
 * Notice that here we don't allow signals to
 * interrupt us.
 *
 * Since WaitQ is now not NULL, this automatically
 * tells the interrupt routine it's time to die. */