简化版udev, 抓取uevent事件

7064阅读　4评论2011-11-09　piaoyizu
分类：LINUX

  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <sys/socket.h>
  4. #include <linux/netlink.h>

  6. struct uevent {
  7.     const char *action;
  8.     const char *path;
  9.     const char *subsystem;
  10.     const char *firmware;
  11.     int major;
  12.     int minor;
  13. };

  15. static int open_uevent_socket(void)
  16. {
  17.     struct sockaddr_nl addr;
  18.     int sz = 64*1024; // XXX larger? udev uses
  19.     int on = 1;
  20.     int s;

  22.     memset(&addr, 0, sizeof(addr));
  23.     addr.nl_family = AF_NETLINK;
  24.     addr.nl_pid = getpid();
  25.     addr.nl_groups = 0xffffffff;

  27.     s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
  28.     if(s < 0)
  29.         return -1;

  31.     setsockopt(s, SOL_SOCKET, SO_RCVBUFFORCE, &sz, sizeof(sz));
  32.     setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));

  34.     if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
  35.         close(s);
  36.         return -1;
  37.     }

  39.     return s;
  40. }

  42. static void parse_event(const char *msg, struct uevent *uevent)
  43. {
  44. #if 1
  45.     uevent->action = "";
  46.     uevent->path = "";
  47.     uevent->subsystem = "";
  48.     uevent->firmware = "";
  49.     uevent->major = -1;
  50.     uevent->minor = -1;

  52.         /* currently ignoring SEQNUM */
  53.     while(*msg) {
  54.         printf("%s\n", msg);
  55.         if(!strncmp(msg, "ACTION=", 7)) {
  56.             msg += 7;
  57.             uevent->action = msg;
  58.         } else if(!strncmp(msg, "DEVPATH=", 8)) {
  59.             msg += 8;
  60.             uevent->path = msg;
  61.         } else if(!strncmp(msg, "SUBSYSTEM=", 10)) {
  62.             msg += 10;
  63.             uevent->subsystem = msg;
  64.         } else if(!strncmp(msg, "FIRMWARE=", 9)) {
  65.             msg += 9;
  66.             uevent->firmware = msg;
  67.         } else if(!strncmp(msg, "MAJOR=", 6)) {
  68.             msg += 6;
  69.             uevent->major = atoi(msg);
  70.         } else if(!strncmp(msg, "MINOR=", 6)) {
  71.             msg += 6;
  72.             uevent->minor = atoi(msg);
  73.         }

  75.             /* advance to after the next \0 */
  76.         while(*msg++)
  77.             ;
  78.     }

  80.     printf("event { '%s', '%s', '%s', '%s', %d, %d }\n",
  81.                     uevent->action, uevent->path, uevent->subsystem,
  82.                     uevent->firmware, uevent->major, uevent->minor);
  83. #endif
  84. }

  86. #define UEVENT_MSG_LEN 1024
  87. void handle_device_fd(int fd)
  88. {
  89.     printf("enter %s\n", __func__);
  90.     for(;;) {
  91.         char msg[UEVENT_MSG_LEN+2];
  92.         char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
  93.         struct iovec iov = {msg, sizeof(msg)};
  94.         struct sockaddr_nl snl;
  95.         struct msghdr hdr = {&snl, sizeof(snl), &iov, 1, cred_msg, sizeof(cred_msg), 0};

  97.         ssize_t n = recvmsg(fd, &hdr, 0);
  98.         if (n <= 0) {
  99.             break;
  100.         }

  102.         if ((snl.nl_groups != 1) || (snl.nl_pid != 0)) {
  103.             /* ignoring non-kernel netlink multicast message */
  104.             continue;
  105.         }

  107.         struct cmsghdr * cmsg = CMSG_FIRSTHDR(&hdr);
  108.         if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
  109.             /* no sender credentials received, ignore message */
  110.             continue;
  111.         }

  113.         struct ucred * cred = (struct ucred *)CMSG_DATA(cmsg);
  114.         if (cred->uid != 0) {
  115.             /* message from non-root user, ignore */
  116.             continue;
  117.         }

  119.         if(n >= UEVENT_MSG_LEN) /* overflow -- discard */
  120.             continue;

  122.         msg[n] = '\0';
  123.         msg[n+1] = '\0';

  125.         struct uevent uevent;
  126.         parse_event(msg, &uevent);
  127.     }
  128. }

  130. int main(void)
  131. {
  132.     int fd = 0;
  133.     
  134.     fd = open_uevent_socket();
  135.     if (fd < 0) {
  136.         printf("error!\n");
  137.         return -1;
  138.     }
  139.     
  140.     handle_device_fd(fd);
  141. }
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