tools/cgroup/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 <err.h>
   9 #include <errno.h>
  10 #include <fcntl.h>
  11 #include <libgen.h>
  12 #include <limits.h>
  13 #include <stdio.h>
  14 #include <string.h>
  15 #include <unistd.h>
  16
  17 #include <sys/eventfd.h>
  18
  19 #define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
  20
  21 int main(int argc, char **argv)
  22 {
  23         int efd = -1;
  24         int cfd = -1;
  25         int event_control = -1;
  26         char event_control_path[PATH_MAX];
  27         char line[LINE_MAX];
  28         int ret;
  29
  30         if (argc != 3)
  31                 errx(1, "%s", USAGE_STR);
  32
  33         cfd = open(argv[1], O_RDONLY);
  34         if (cfd == -1)
  35                 err(1, "Cannot open %s", argv[1]);
  36
  37         ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
  38                         dirname(argv[1]));
  39         if (ret >= PATH_MAX)
  40                 errx(1, "Path to cgroup.event_control is too long");
  41
  42         event_control = open(event_control_path, O_WRONLY);
  43         if (event_control == -1)
  44                 err(1, "Cannot open %s", event_control_path);
  45
  46         efd = eventfd(0, 0);
  47         if (efd == -1)
  48                 err(1, "eventfd() failed");
  49
  50         ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
  51         if (ret >= LINE_MAX)
  52                 errx(1, "Arguments string is too long");
  53
  54         ret = write(event_control, line, strlen(line) + 1);
  55         if (ret == -1)
  56                 err(1, "Cannot write to cgroup.event_control");
  57
  58         while (1) {
  59                 uint64_t result;
  60
  61                 ret = read(efd, &result, sizeof(result));
  62                 if (ret == -1) {
  63                         if (errno == EINTR)
  64                                 continue;
  65                         err(1, "Cannot read from eventfd");
  66                 }
  67                 assert(ret == sizeof(result));
  68
  69                 ret = access(event_control_path, W_OK);
  70                 if ((ret == -1) && (errno == ENOENT)) {
  71                         puts("The cgroup seems to have removed.");
  72                         break;
  73                 }
  74
  75                 if (ret == -1)
  76                         err(1, "cgroup.event_control is not accessible any more");
  77
  78                 printf("%s %s: crossed\n", argv[1], argv[2]);
  79         }
  80
  81         return 0;
  82 }