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 | } |
108 | |