LDD3 sleepy 模块

LDD3 chapter6 sleepy模块在源代码的 misc-modules文件夹中。是一个简单的休眠-唤醒的例子。

sleepy.c

/*
 * sleepy.c -- the writers awake the readers
 *
 * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
 * Copyright (C) 2001 O'Reilly & Associates
 *
 * The source code in this file can be freely used, adapted,
 * and redistributed in source or binary form, so long as an
 * acknowledgment appears in derived source files.  The citation
 * should list that the code comes from the book "Linux Device
 * Drivers" by Alessandro Rubini and Jonathan Corbet, published
 * by O'Reilly & Associates.   No warranty is attached;
 * we cannot take responsibility for errors or fitness for use.
 *
 * $Id: sleepy.c,v 1.7 2004/09/26 07:02:43 gregkh Exp $
 */

#include <linux/module.h>
#include <linux/init.h>

#include <linux/sched.h>  /* current and everything */
#include <linux/kernel.h> /* printk() */
#include <linux/fs.h>     /* everything... */
#include <linux/types.h>  /* size_t */
#include <linux/wait.h>

MODULE_LICENSE("Dual BSD/GPL");

static int sleepy_major = 0;

static DECLARE_WAIT_QUEUE_HEAD(wq);
static int flag = 0;

ssize_t sleepy_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
{
	printk(KERN_DEBUG "process %i (%s) going to sleep\n",
			current->pid, current->comm);
	wait_event_interruptible(wq, flag != 0);
	flag = 0;
	printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);
	return 0; /* EOF */
}

ssize_t sleepy_write (struct file *filp, const char __user *buf, size_t count,
		loff_t *pos)
{
	printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",
			current->pid, current->comm);
	flag = 1;
	wake_up_interruptible(&wq);
	return count; /* succeed, to avoid retrial */
}


struct file_operations sleepy_fops = {
	.owner = THIS_MODULE,
	.read =  sleepy_read,
	.write = sleepy_write,
};


int sleepy_init(void)
{
	int result;

	/*
	 * Register your major, and accept a dynamic number
	 */
	result = register_chrdev(sleepy_major, "sleepy", &sleepy_fops);
	if (result < 0)
		return result;
	if (sleepy_major == 0)
		sleepy_major = result; /* dynamic */
	return 0;
}

void sleepy_cleanup(void)
{
	unregister_chrdev(sleepy_major, "sleepy");
}

module_init(sleepy_init);
module_exit(sleepy_cleanup);

Makefile:

KERN_DIR = /run/media/huntinux/F/huntinux_work/embeded_world/linux_kernel/mini2440-linux2.6.32.2

all:
    make -C $(KERN_DIR) M=`pwd` modules

clean:
    make -C $(KERN_DIR) M=`pwd` modules clean
    rm -rf modules.order

install:
    cp *.ko /nfs/busybox/fs_mini2440

obj-m    := sleepy.o

其中KERN_DIR变量表示内核源代码的目录，我用的是 2.6.32.2内核。

/nfs/busybox/fs_mini2440 是网络文件系统的根目录。

在pc机上

#make
#make install

然后开发板从网络挂在文件系统。

插入模块，并查询主设备号。（应为是动态分配，所以需要查询得到主设备号，然后使用该主设备号创建设备节点）

# insmod sleepy.ko

# cat /proc/devices  | grep "sleepy"
253 sleepy

在开发板上手动创建设备节点：

# mknod /dev/sleepy c 253 0

测试驱动：

# cat /dev/sleepy &

发现process ... going to sleep 没有打印出来。

原因很简单： 当前日志级别的数值 小于 KERN_DEBUG。数值越小优先级越高。见LDD chapter4 讲解printk的内容。

解决办法：修改当前日志级别为8即可：

# echo 8 >/proc/sys/kernel/printk
# cat /dev/sleepy &
process 680 (cat) going to sleep

对/dev/sleepy读的设备会休眠。

# echo "data">/dev/sleepy 
process 657 (sh) awakening the readers...
awoken 678 (cat)

写/dev/sleepy 会唤醒休眠的进程。

此外，手动创建节点太麻烦，与书上前几章的方法一样，用脚本实现自动创建节点。

sleey_load.sh:

#!/bin/sh

module="sleepy"
device="sleepy"
mode="664"

/sbin/insmod ./$module.ko $* || exit 1
major=$(awk "\$2==\"$module\" {print \$1}" /proc/devices)

rm -f /dev/${device}
mknod /dev/${device} c $major 0

在开发板上，执行该脚本即可完成装载模块，创建节点的任务。