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// SPDX-License-Identifier: GPL-2.0
#include <linux/stringify.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "fs.h"
struct cgroupfs_cache_entry {
char subsys[32];
char mountpoint[PATH_MAX];
};
/* just cache last used one */
static struct cgroupfs_cache_entry cached;
int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
{
FILE *fp;
char *line = NULL;
size_t len = 0;
char *p, *path;
char mountpoint[PATH_MAX];
if (!strcmp(cached.subsys, subsys)) {
if (strlen(cached.mountpoint) < maxlen) {
strcpy(buf, cached.mountpoint);
return 0;
}
return -1;
}
fp = fopen("/proc/mounts", "r");
if (!fp)
return -1;
/*
* in order to handle split hierarchy, we need to scan /proc/mounts
* and inspect every cgroupfs mount point to find one that has
* the given subsystem. If we found v1, just use it. If not we can
* use v2 path as a fallback.
*/
mountpoint[0] = '\0';
/*
* The /proc/mounts has the follow format:
*
* <devname> <mount point> <fs type> <options> ...
*
*/
while (getline(&line, &len, fp) != -1) {
/* skip devname */
p = strchr(line, ' ');
if (p == NULL)
continue;
/* save the mount point */
path = ++p;
p = strchr(p, ' ');
if (p == NULL)
continue;
*p++ = '\0';
/* check filesystem type */
if (strncmp(p, "cgroup", 6))
continue;
if (p[6] == '2') {
/* save cgroup v2 path */
strcpy(mountpoint, path);
continue;
}
/* now we have cgroup v1, check the options for subsystem */
p += 7;
p = strstr(p, subsys);
if (p == NULL)
continue;
/* sanity check: it should be separated by a space or a comma */
if (!strchr(" ,", p[-1]) || !strchr(" ,", p[strlen(subsys)]))
continue;
strcpy(mountpoint, path);
break;
}
free(line);
fclose(fp);
strncpy(cached.subsys, subsys, sizeof(cached.subsys) - 1);
strcpy(cached.mountpoint, mountpoint);
if (mountpoint[0] && strlen(mountpoint) < maxlen) {
strcpy(buf, mountpoint);
return 0;
}
return -1;
}
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