1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/stringify.h>
 3#include <sys/types.h>
 4#include <sys/stat.h>
 5#include <fcntl.h>
 6#include <stdio.h>
 7#include <stdlib.h>
 8#include <string.h>
 9#include "fs.h"
10
11int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
12{
13	FILE *fp;
14	char mountpoint[PATH_MAX + 1], tokens[PATH_MAX + 1], type[PATH_MAX + 1];
15	char path_v1[PATH_MAX + 1], path_v2[PATH_MAX + 2], *path;
16	char *token, *saved_ptr = NULL;
17
18	fp = fopen("/proc/mounts", "r");
19	if (!fp)
20		return -1;
21
22	/*
23	 * in order to handle split hierarchy, we need to scan /proc/mounts
24	 * and inspect every cgroupfs mount point to find one that has
25	 * perf_event subsystem
26	 */
27	path_v1[0] = '\0';
28	path_v2[0] = '\0';
29
30	while (fscanf(fp, "%*s %"__stringify(PATH_MAX)"s %"__stringify(PATH_MAX)"s %"
31				__stringify(PATH_MAX)"s %*d %*d\n",
32				mountpoint, type, tokens) == 3) {
33
34		if (!path_v1[0] && !strcmp(type, "cgroup")) {
35
36			token = strtok_r(tokens, ",", &saved_ptr);
37
38			while (token != NULL) {
39				if (subsys && !strcmp(token, subsys)) {
40					strcpy(path_v1, mountpoint);
41					break;
42				}
43				token = strtok_r(NULL, ",", &saved_ptr);
44			}
45		}
46
47		if (!path_v2[0] && !strcmp(type, "cgroup2"))
48			strcpy(path_v2, mountpoint);
49
50		if (path_v1[0] && path_v2[0])
51			break;
52	}
53	fclose(fp);
54
55	if (path_v1[0])
56		path = path_v1;
57	else if (path_v2[0])
58		path = path_v2;
59	else
60		return -1;
61
62	if (strlen(path) < maxlen) {
63		strcpy(buf, path);
64		return 0;
65	}
66	return -1;
67}