// SPDX-License-Identifier: GPL-2.0 /* * cgroup_event_listener.c - Simple listener of cgroup events * * Copyright (C) Kirill A. Shutemov <kirill@shutemov.name> */ #include <assert.h> #include <err.h> #include <errno.h> #include <fcntl.h> #include <libgen.h> #include <limits.h> #include <stdio.h> #include <string.h> #include <unistd.h> #include <sys/eventfd.h> #define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>" int main(int argc, char **argv) { int efd = -1; int cfd = -1; int event_control = -1; char event_control_path[PATH_MAX]; char line[LINE_MAX]; int ret; if (argc != 3) errx(1, "%s", USAGE_STR); cfd = open(argv[1], O_RDONLY); if (cfd == -1) err(1, "Cannot open %s", argv[1]); ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control", dirname(argv[1])); if (ret >= PATH_MAX) errx(1, "Path to cgroup.event_control is too long"); event_control = open(event_control_path, O_WRONLY); if (event_control == -1) err(1, "Cannot open %s", event_control_path); efd = eventfd(0, 0); if (efd == -1) err(1, "eventfd() failed"); ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]); if (ret >= LINE_MAX) errx(1, "Arguments string is too long"); ret = write(event_control, line, strlen(line) + 1); if (ret == -1) err(1, "Cannot write to cgroup.event_control"); while (1) { uint64_t result; ret = read(efd, &result, sizeof(result)); if (ret == -1) { if (errno == EINTR) continue; err(1, "Cannot read from eventfd"); } assert(ret == sizeof(result)); ret = access(event_control_path, W_OK); if ((ret == -1) && (errno == ENOENT)) { puts("The cgroup seems to have removed."); break; } if (ret == -1) err(1, "cgroup.event_control is not accessible any more"); printf("%s %s: crossed\n", argv[1], argv[2]); } return 0; }