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/*
* cgroup_event_listener.c - Simple listener of cgroup events
*
* Copyright (C) Kirill A. Shutemov <kirill@shutemov.name>
*/
#include <assert.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>\n"
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) {
fputs(USAGE_STR, stderr);
return 1;
}
cfd = open(argv[1], O_RDONLY);
if (cfd == -1) {
fprintf(stderr, "Cannot open %s: %s\n", argv[1],
strerror(errno));
goto out;
}
ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
dirname(argv[1]));
if (ret >= PATH_MAX) {
fputs("Path to cgroup.event_control is too long\n", stderr);
goto out;
}
event_control = open(event_control_path, O_WRONLY);
if (event_control == -1) {
fprintf(stderr, "Cannot open %s: %s\n", event_control_path,
strerror(errno));
goto out;
}
efd = eventfd(0, 0);
if (efd == -1) {
perror("eventfd() failed");
goto out;
}
ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
if (ret >= LINE_MAX) {
fputs("Arguments string is too long\n", stderr);
goto out;
}
ret = write(event_control, line, strlen(line) + 1);
if (ret == -1) {
perror("Cannot write to cgroup.event_control");
goto out;
}
while (1) {
uint64_t result;
ret = read(efd, &result, sizeof(result));
if (ret == -1) {
if (errno == EINTR)
continue;
perror("Cannot read from eventfd");
break;
}
assert(ret == sizeof(result));
ret = access(event_control_path, W_OK);
if ((ret == -1) && (errno == ENOENT)) {
puts("The cgroup seems to have removed.");
ret = 0;
break;
}
if (ret == -1) {
perror("cgroup.event_control "
"is not accessible any more");
break;
}
printf("%s %s: crossed\n", argv[1], argv[2]);
}
out:
if (efd >= 0)
close(efd);
if (event_control >= 0)
close(event_control);
if (cfd >= 0)
close(cfd);
return (ret != 0);
}
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