linux/tools/cgroup/cgroup_event_listener.c
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   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
  21int 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}
  83
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