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Based on kernel version 3.8. Page generated on 2013-02-20 21:47 EST.

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 <errno.h>
9	#include <fcntl.h>
10	#include <libgen.h>
11	#include <limits.h>
12	#include <stdio.h>
13	#include <string.h>
14	#include <unistd.h>
15	
16	#include <sys/eventfd.h>
17	
18	#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>\n"
19	
20	int main(int argc, char **argv)
21	{
22		int efd = -1;
23		int cfd = -1;
24		int event_control = -1;
25		char event_control_path[PATH_MAX];
26		char line[LINE_MAX];
27		int ret;
28	
29		if (argc != 3) {
30			fputs(USAGE_STR, stderr);
31			return 1;
32		}
33	
34		cfd = open(argv[1], O_RDONLY);
35		if (cfd == -1) {
36			fprintf(stderr, "Cannot open %s: %s\n", argv[1],
37					strerror(errno));
38			goto out;
39		}
40	
41		ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
42				dirname(argv[1]));
43		if (ret >= PATH_MAX) {
44			fputs("Path to cgroup.event_control is too long\n", stderr);
45			goto out;
46		}
47	
48		event_control = open(event_control_path, O_WRONLY);
49		if (event_control == -1) {
50			fprintf(stderr, "Cannot open %s: %s\n", event_control_path,
51					strerror(errno));
52			goto out;
53		}
54	
55		efd = eventfd(0, 0);
56		if (efd == -1) {
57			perror("eventfd() failed");
58			goto out;
59		}
60	
61		ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
62		if (ret >= LINE_MAX) {
63			fputs("Arguments string is too long\n", stderr);
64			goto out;
65		}
66	
67		ret = write(event_control, line, strlen(line) + 1);
68		if (ret == -1) {
69			perror("Cannot write to cgroup.event_control");
70			goto out;
71		}
72	
73		while (1) {
74			uint64_t result;
75	
76			ret = read(efd, &result, sizeof(result));
77			if (ret == -1) {
78				if (errno == EINTR)
79					continue;
80				perror("Cannot read from eventfd");
81				break;
82			}
83			assert(ret == sizeof(result));
84	
85			ret = access(event_control_path, W_OK);
86			if ((ret == -1) && (errno == ENOENT)) {
87					puts("The cgroup seems to have removed.");
88					ret = 0;
89					break;
90			}
91	
92			if (ret == -1) {
93				perror("cgroup.event_control "
94						"is not accessible any more");
95				break;
96			}
97	
98			printf("%s %s: crossed\n", argv[1], argv[2]);
99		}
100	
101	out:
102		if (efd >= 0)
103			close(efd);
104		if (event_control >= 0)
105			close(event_control);
106		if (cfd >= 0)
107			close(cfd);
108	
109		return (ret != 0);
110	}
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