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 } 83