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// 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;
}
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