Documentation/cgroups/cgroup_event_listener.c

   1 /*
   2  * cgroup_event_listener.c - Simple listener of cgroup events
   3  *
   4  * Copyright (C) Kirill A. Shutemov <kirill@shutemov.name>
   5  */
   6
   7 #include <assert.h>
   8 #include <errno.h>
   9 #include <fcntl.h>
  10 #include <libgen.h>
  11 #include <limits.h>
  12 #include <stdio.h>
  13 #include <string.h>
  14 #include <unistd.h>
  15
  16 #include <sys/eventfd.h>
  17
  18 #define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>\n"
  19
  20 int main(int argc, char **argv)
  21 {
  22         int efd = -1;
  23         int cfd = -1;
  24         int event_control = -1;
  25         char event_control_path[PATH_MAX];
  26         char line[LINE_MAX];
  27         int ret;
  28
  29         if (argc != 3) {
  30                 fputs(USAGE_STR, stderr);
  31                 return 1;
  32         }
  33
  34         cfd = open(argv[1], O_RDONLY);
  35         if (cfd == -1) {
  36                 fprintf(stderr, "Cannot open %s: %s\n", argv[1],
  37                                 strerror(errno));
  38                 goto out;
  39         }
  40
  41         ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
  42                         dirname(argv[1]));
  43         if (ret >= PATH_MAX) {
  44                 fputs("Path to cgroup.event_control is too long\n", stderr);
  45                 goto out;
  46         }
  47
  48         event_control = open(event_control_path, O_WRONLY);
  49         if (event_control == -1) {
  50                 fprintf(stderr, "Cannot open %s: %s\n", event_control_path,
  51                                 strerror(errno));
  52                 goto out;
  53         }
  54
  55         efd = eventfd(0, 0);
  56         if (efd == -1) {
  57                 perror("eventfd() failed");
  58                 goto out;
  59         }
  60
  61         ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
  62         if (ret >= LINE_MAX) {
  63                 fputs("Arguments string is too long\n", stderr);
  64                 goto out;
  65         }
  66
  67         ret = write(event_control, line, strlen(line) + 1);
  68         if (ret == -1) {
  69                 perror("Cannot write to cgroup.event_control");
  70                 goto out;
  71         }
  72
  73         while (1) {
  74                 uint64_t result;
  75
  76                 ret = read(efd, &result, sizeof(result));
  77                 if (ret == -1) {
  78                         if (errno == EINTR)
  79                                 continue;
  80                         perror("Cannot read from eventfd");
  81                         break;
  82                 }
  83                 assert(ret == sizeof(result));
  84
  85                 ret = access(event_control_path, W_OK);
  86                 if ((ret == -1) && (errno == ENOENT)) {
  87                                 puts("The cgroup seems to have removed.");
  88                                 ret = 0;
  89                                 break;
  90                 }
  91
  92                 if (ret == -1) {
  93                         perror("cgroup.event_control "
  94                                         "is not accessible any more");
  95                         break;
  96                 }
  97
  98                 printf("%s %s: crossed\n", argv[1], argv[2]);
  99         }
 100
 101 out:
 102         if (efd >= 0)
 103                 close(efd);
 104         if (event_control >= 0)
 105                 close(event_control);
 106         if (cfd >= 0)
 107                 close(cfd);
 108
 109         return (ret != 0);
 110 }