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。