LXR linux/tools/cgroup/cgroup_event

   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 <kirill@shutemov.name>
   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
  22int 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}
  84