tools/cgroup/cgroup_event_listener.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * cgroup_event_listener.c - Simple listener of cgroup events
   4  *
   5  * Copyright (C) Kirill A. Shutemov <[email protected]>
   6  */
   7
   8 #include <assert.h>
   9 #include <err.h>
  10 #include <errno.h>
  11 #include <fcntl.h>
  12 #include <libgen.h>
  13 #include <limits.h>
  14 #include <stdio.h>
  15 #include <string.h>
  16 #include <unistd.h>
  17
  18 #include <sys/eventfd.h>
  19
  20 #define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"
  21
  22 int main(int argc, char **argv)
  23 {
  24         int efd = -1;
  25         int cfd = -1;
  26         int event_control = -1;
  27         char event_control_path[PATH_MAX];
  28         char line[LINE_MAX];
  29         int ret;
  30
  31         if (argc != 3)
  32                 errx(1, "%s", USAGE_STR);
  33
  34         cfd = open(argv[1], O_RDONLY);
  35         if (cfd == -1)
  36                 err(1, "Cannot open %s", argv[1]);
  37
  38         ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
  39                         dirname(argv[1]));
  40         if (ret >= PATH_MAX)
  41                 errx(1, "Path to cgroup.event_control is too long");
  42
  43         event_control = open(event_control_path, O_WRONLY);
  44         if (event_control == -1)
  45                 err(1, "Cannot open %s", event_control_path);
  46
  47         efd = eventfd(0, 0);
  48         if (efd == -1)
  49                 err(1, "eventfd() failed");
  50
  51         ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
  52         if (ret >= LINE_MAX)
  53                 errx(1, "Arguments string is too long");
  54
  55         ret = write(event_control, line, strlen(line) + 1);
  56         if (ret == -1)
  57                 err(1, "Cannot write to cgroup.event_control");
  58
  59         while (1) {
  60                 uint64_t result;
  61
  62                 ret = read(efd, &result, sizeof(result));
  63                 if (ret == -1) {
  64                         if (errno == EINTR)
  65                                 continue;
  66                         err(1, "Cannot read from eventfd");
  67                 }
  68                 assert(ret == sizeof(result));
  69
  70                 ret = access(event_control_path, W_OK);
  71                 if ((ret == -1) && (errno == ENOENT)) {
  72                         puts("The cgroup seems to have removed.");
  73                         break;
  74                 }
  75
  76                 if (ret == -1)
  77                         err(1, "cgroup.event_control is not accessible any more");
  78
  79                 printf("%s %s: crossed\n", argv[1], argv[2]);
  80         }
  81
  82         return 0;
  83 }