tools/lib/api/fs/cgroup.c

   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
  11 struct cgroupfs_cache_entry {
  12         char    subsys[32];
  13         char    mountpoint[PATH_MAX];
  14 };
  15
  16 /* just cache last used one */
  17 static struct cgroupfs_cache_entry *cached;
  18
  19 int cgroupfs_find_mountpoint(char *buf, size_t maxlen, const char *subsys)
  20 {
  21         FILE *fp;
  22         char *line = NULL;
  23         size_t len = 0;
  24         char *p, *path;
  25         char mountpoint[PATH_MAX];
  26
  27         if (cached && !strcmp(cached->subsys, subsys)) {
  28                 if (strlen(cached->mountpoint) < maxlen) {
  29                         strcpy(buf, cached->mountpoint);
  30                         return 0;
  31                 }
  32                 return -1;
  33         }
  34
  35         fp = fopen("/proc/mounts", "r");
  36         if (!fp)
  37                 return -1;
  38
  39         /*
  40          * in order to handle split hierarchy, we need to scan /proc/mounts
  41          * and inspect every cgroupfs mount point to find one that has
  42          * the given subsystem.  If we found v1, just use it.  If not we can
  43          * use v2 path as a fallback.
  44          */
  45         mountpoint[0] = '\0';
  46
  47         /*
  48          * The /proc/mounts has the follow format:
  49          *
  50          *   <devname> <mount point> <fs type> <options> ...
  51          *
  52          */
  53         while (getline(&line, &len, fp) != -1) {
  54                 /* skip devname */
  55                 p = strchr(line, ' ');
  56                 if (p == NULL)
  57                         continue;
  58
  59                 /* save the mount point */
  60                 path = ++p;
  61                 p = strchr(p, ' ');
  62                 if (p == NULL)
  63                         continue;
  64
  65                 *p++ = '\0';
  66
  67                 /* check filesystem type */
  68                 if (strncmp(p, "cgroup", 6))
  69                         continue;
  70
  71                 if (p[6] == '2') {
  72                         /* save cgroup v2 path */
  73                         strcpy(mountpoint, path);
  74                         continue;
  75                 }
  76
  77                 /* now we have cgroup v1, check the options for subsystem */
  78                 p += 7;
  79
  80                 p = strstr(p, subsys);
  81                 if (p == NULL)
  82                         continue;
  83
  84                 /* sanity check: it should be separated by a space or a comma */
  85                 if (!strchr(" ,", p[-1]) || !strchr(" ,", p[strlen(subsys)]))
  86                         continue;
  87
  88                 strcpy(mountpoint, path);
  89                 break;
  90         }
  91         free(line);
  92         fclose(fp);
  93
  94         if (!cached)
  95                 cached = calloc(1, sizeof(*cached));
  96
  97         if (cached) {
  98                 strncpy(cached->subsys, subsys, sizeof(cached->subsys) - 1);
  99                 strcpy(cached->mountpoint, mountpoint);
 100         }
 101
 102         if (mountpoint[0] && strlen(mountpoint) < maxlen) {
 103                 strcpy(buf, mountpoint);
 104                 return 0;
 105         }
 106         return -1;
 107 }