udev（九）-- 写个程序检测我们的设备插拔

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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。