udev（九）-- 写个程序检测我们的设备插拔

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：

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1. #include <unistd.h>   
2. #include <stdio.h>   
3. #include <stdlib.h>   
4. #include <stddef.h>   
5. #include <string.h>   
6. #include <errno.h>   
7. #include <getopt.h>   
8. #include <fcntl.h>   
9. #include <errno.h>   
10. #include <signal.h>   
11. #include <getopt.h>   
12. #include <sys/time.h>   
13. #include <sys/socket.h>   
14. #include <sys/un.h>   
15. #include <sys/select.h>   
16. #include <linux/types.h>   
17. #include <linux/netlink.h>   
18. #undef asmlinkage   
19. #ifdef __i386__   
20. #define asmlinkage __attribute__((regparm(0)))   
21. #else   
22. #define asmlinkage    
23. #endif   
24. #define UDEV_MAX(a,b) ((a) > (b) ? (a) : (b))   
25. #define udev_list_entry_foreach(entry, first) /   
26.     for  (entry = first; /  
27.          entry != NULL; /  
28.          entry = udev_list_entry_get_next(entry))  
29. static   int  debug;  
30. static   int  udev_exit;  
31. static   void  asmlinkage sig_handler( int  signum)  
32. {  
33.     if  (signum == SIGINT || signum == SIGTERM)  
34.         udev_exit = 1;  
35. }  
36. static   void  print_device( struct  udev_device *device,  const   char  *source,  int  env)  
37. {  
38.     struct  timeval tv;  
39.     struct  timezone tz;  
40.     gettimeofday(&tv, &tz);  
41.     printf("%-6s[%llu.%06u] %-8s %s (%s)/n" ,  
42.            source,  
43.            (unsigned long   long ) tv.tv_sec, (unsigned  int ) tv.tv_usec,  
44.            udev_device_get_action(device),  
45.            udev_device_get_devpath(device),  
46.            udev_device_get_subsystem(device));  
47.     if  (env) {  
48.         struct  udev_list_entry *list_entry;  
49.         udev_list_entry_foreach(list_entry, udev_device_get_properties_list_entry(device))  
50.             printf("%s=%s/n" ,  
51.                    udev_list_entry_get_name(list_entry),  
52.                    udev_list_entry_get_value(list_entry));  
53.         printf("/n" );  
54.     }  
55. }  
56. int  udevadm_monitor( struct  udev *udev)  
57. {  
58.     struct  sigaction act;  
59.     int  env = 0;  
60.     int  print_kernel = 0;  
61.     int  print_udev = 0;  
62.     struct  udev_monitor *udev_monitor = NULL;  
63.     struct  udev_monitor *kernel_monitor = NULL;  
64.     fd_set readfds;  
65.     int  rc = 0;  
66.     if  (!print_kernel && !print_udev) {  
67.         print_kernel = 1;  
68.         print_udev =1;  
69.     }  
70.     if  (getuid() != 0 && print_kernel) {  
71.         fprintf(stderr, "root privileges needed to subscribe to kernel events/n" );  
72.         goto  out;  
73.     }  
74.     /* set signal handlers */   
75.     memset(&act, 0x00, sizeof ( struct  sigaction));  
76.     act.sa_handler = (void  (*)( int )) sig_handler;  
77.     sigemptyset(&act.sa_mask);  
78.     act.sa_flags = SA_RESTART;  
79.     sigaction(SIGINT, &act, NULL);  
80.     sigaction(SIGTERM, &act, NULL);  
81.     printf("monitor will print the received events for:/n" );  
82.     if  (print_udev) {  
83.         udev_monitor = udev_monitor_new_from_socket(udev, "@/org/kernel/udev/monitor" );  
84.         if  (udev_monitor == NULL) {  
85.             rc = 1;  
86.             goto  out;  
87.         }  
88.         if  (udev_monitor_enable_receiving(udev_monitor) < 0) {  
89.             rc = 2;  
90.             goto  out;  
91.         }  
92.         printf("UDEV the event which udev sends out after rule processing/n" );  
93.     }  
94.       
95.     if  (print_kernel) {  
96.         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   
97.         if  (kernel_monitor == NULL) {  
98.             rc = 3;  
99.             printf("udev_monitor_new_from_netlink() error/n" );  
100.             goto  out;  
101.         }  
102.         if  (udev_monitor_enable_receiving(kernel_monitor) < 0) {  
103.             rc = 4;  
104.             goto  out;  
105.         }  
106.         printf("UEVENT the kernel uevent/n" );  
107.     }  
108.       
109.     printf("/n" );  
110.     while  (!udev_exit) {  
111.         int  fdcount;  
112.         FD_ZERO(&readfds);  
113.         if  (kernel_monitor != NULL)  
114.             FD_SET(udev_monitor_get_fd(kernel_monitor), &readfds);  
115.         if  (udev_monitor != NULL)  
116.             FD_SET(udev_monitor_get_fd(udev_monitor), &readfds);  
117.         fdcount = select(UDEV_MAX(udev_monitor_get_fd(kernel_monitor), udev_monitor_get_fd(udev_monitor))+1,  
118.                  &readfds, NULL, NULL, NULL);  
119.         if  (fdcount < 0) {  
120.             if  (errno != EINTR)  
121.                 fprintf(stderr, "error receiving uevent message: %m/n" );  
122.             continue ;  
123.         }  
124.         if  ((kernel_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(kernel_monitor), &readfds)) {  
125.             struct  udev_device *device;  
126.             device = udev_monitor_receive_device(kernel_monitor);  
127.             if  (device == NULL)  
128.                 continue ;  
129.             print_device(device, "UEVENT" , env);  
130.             udev_device_unref(device);  
131.         }  
132.         if  ((udev_monitor != NULL) && FD_ISSET(udev_monitor_get_fd(udev_monitor), &readfds)) {  
133.             struct  udev_device *device;  
134.             device = udev_monitor_receive_device(udev_monitor);  
135.             if  (device == NULL)  
136.                 continue ;  
137.             print_device(device, "UDEV" , env);  
138.             udev_device_unref(device);  
139.         }  
140.     }  
141. out:  
142.     udev_monitor_unref(udev_monitor);  
143.     udev_monitor_unref(kernel_monitor);  
144.     return  rc;  
145. }  
146. int  main( int  argc,  char  *argv[])  
147. {  
148.     struct  udev *udev;  
149.     int  rc = 1;  
150.     udev = udev_new();  
151.     if  (udev == NULL)  
152.         goto  out;  
153.     udevadm_monitor(udev);  
154.     goto  out;  
155.     rc = 2;  
156. out:  
157.     udev_unref(udev);  
158.     return  rc;  
159. }  

#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

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

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。/

来源：http://blog.youkuaiyun.com/fjb2080/archive/2009/12/15/5009791.aspx