udev(九)-- 写个程序检测我们的设备插拔

长平狐 发布于 2013/01/11 10:33
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       原创文章,转载请注明出处,谢谢!       
       作者:清林,博客名:飞空静渡

 

在这个教程里我将写一个程序,其作用是检测系统的设备插拔事件,当有设备插入系统时,就可以检测到这个设备并把设备的信息显示出来,如果设备从系统里移除,也同样可以检测出来,并移除设备。这个代码是参考了udev-139的源码的,如果读者有兴趣也可以参考udev的源码。其中在udev-139代码中有个小小的错误,我将在下面的代码中说出。

 

首先先说一下udev的一个命令,你可以在控制台下运行:

udevadm  monitor

我的运行如下图所示:


当插入我的金士顿优盘时,便可以检测到优盘的插入,如下图:


我们现在要做就是写个程序,其输出和上面的一样,其实也就是udevadm的源码,我只是把它的大部分代码移除,只留个检测插拔事件的代码,并把很多地方的宏和函数集成到一个文件中。其中具体代码的API可参考libudev Reference Manual的说明:http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/ch01.html


下面是源代码udevadm.c:

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <getopt.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <getopt.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <linux/types.h>
#include <linux/netlink.h>
#undef asmlinkage
#ifdef __i386__
#define asmlinkage __attribute__((regparm(0)))
#else
#define asmlinkage 
#endif
#define UDEV_MAX(a,b) ((a) > (b) ? (a) : (b))
#define udev_list_entry_foreach(entry, first) /
	for (entry = first; /
	     entry != NULL; /
	     entry = udev_list_entry_get_next(entry))
static int debug;
static int udev_exit;
static void asmlinkage sig_handler(int signum)
{
	if (signum == SIGINT || signum == SIGTERM)
		udev_exit = 1;
}
static void print_device(struct udev_device *device, const char *source, int env)
{
	struct timeval tv;
	struct timezone tz;
	gettimeofday(&tv, &tz);
	printf("%-6s[%llu.%06u] %-8s %s (%s)/n",
	       source,
	       (unsigned long long) tv.tv_sec, (unsigned int) tv.tv_usec,
	       udev_device_get_action(device),
	       udev_device_get_devpath(device),
	       udev_device_get_subsystem(device));
	if (env) {
		struct udev_list_entry *list_entry;
		udev_list_entry_foreach(list_entry, udev_device_get_properties_list_entry(device))
			printf("%s=%s/n",
			       udev_list_entry_get_name(list_entry),
			       udev_list_entry_get_value(list_entry));
		printf("/n");
	}
}
int udevadm_monitor(struct udev *udev)
{
	struct sigaction act;
	int env = 0;
	int print_kernel = 0;
	int print_udev = 0;
	struct udev_monitor *udev_monitor = NULL;
	struct udev_monitor *kernel_monitor = NULL;
	fd_set readfds;
	int rc = 0;
	if (!print_kernel && !print_udev) {
		print_kernel = 1;
		print_udev =1;
	}
	if (getuid() != 0 && print_kernel) {
		fprintf(stderr, "root privileges needed to subscribe to kernel events/n");
		goto out;
	}
	/* set signal handlers */
	memset(&act, 0x00, sizeof(struct sigaction));
	act.sa_handler = (void (*)(int)) sig_handler;
	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_RESTART;
	sigaction(SIGINT, &act, NULL);
	sigaction(SIGTERM, &act, NULL);
	printf("monitor will print the received events for:/n");
	if (print_udev) {
		udev_monitor = udev_monitor_new_from_socket(udev, "@/org/kernel/udev/monitor");
		if (udev_monitor == NULL) {
			rc = 1;
			goto out;
		}
		if (udev_monitor_enable_receiving(udev_monitor) < 0) {
			rc = 2;
			goto out;
		}
		printf("UDEV the event which udev sends out after rule processing/n");
	}
	
	if (print_kernel) {
		kernel_monitor = udev_monitor_new_from_netlink(udev, "udev"); //这里的udev源码中没有"udev"这个参数,不加进去返回值就为NULL,所以要加这个
		if (kernel_monitor == NULL) {
			rc = 3;
			printf("udev_monitor_new_from_netlink() error/n");
			goto out;
		}
		if (udev_monitor_enable_receiving(kernel_monitor) < 0) {
			rc = 4;
			goto out;
		}
		printf("UEVENT the kernel uevent/n");
	}
	
	printf("/n");
	while (!udev_exit) {
		int fdcount;
		FD_ZERO(&readfds);
		if (kernel_monitor != NULL)
			FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);
		if (udev_monitor != NULL)
			FD_SET(udev_monitor_get_fd(udev_monitor), &readfds);
		fdcount = select(UDEV_MAX(udev_monitor_get_fd(kernel_monitor), udev_monitor_get_fd(udev_monitor))+1,
				 &readfds, NULL, NULL, NULL);
		if (fdcount < 0) {
			if (errno != EINTR)
				fprintf(stderr, "error receiving uevent message: %m/n");
			continue;
		}
		if ((kernel_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(kernel_monitor), &readfds)) {
			struct udev_device *device;
			device = udev_monitor_receive_device(kernel_monitor);
			if (device == NULL)
				continue;
			print_device(device, "UEVENT", env);
			udev_device_unref(device);
		}
		if ((udev_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(udev_monitor), &readfds)) {
			struct udev_device *device;
			device = udev_monitor_receive_device(udev_monitor);
			if (device == NULL)
				continue;
			print_device(device, "UDEV", env);
			udev_device_unref(device);
		}
	}
out:
	udev_monitor_unref(udev_monitor);
	udev_monitor_unref(kernel_monitor);
	return rc;
}
int main(int argc, char *argv[])
{
	struct udev *udev;
	int rc = 1;
	udev = udev_new();
	if (udev == NULL)
		goto out;
	udevadm_monitor(udev);
	goto out;
	rc = 2;
out:
	udev_unref(udev);
	return rc;
}

 

下面是Makefile

myudevadm: udevadm.c
       gcc -g -Wall -ludev udevadm.c -o myudevadm

 

当插入和拔出优盘是的显示如下图:



记得加个sudo,要退出按ctrl-c,我的运行环境是ubuntu9.10。可看到我的优盘设备是sde,有关分区是sde4,这个你可以在/dev目录下找到,并且是usb设备。


原文链接:http://blog.csdn.net/fjb2080/article/details/5009791
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