1 /* find-mount-point.c -- find the root mount point for a file.
2 Copyright (C) 2010-2023 Free Software Foundation, Inc.
3
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation, either version 3 of the License, or
7 (at your option) any later version.
8
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <https://www.gnu.org/licenses/>. */
16
17 #include <config.h>
18 #include <sys/types.h>
19
20 #include "system.h"
21 #include "save-cwd.h"
22 #include "xgetcwd.h"
23 #include "find-mount-point.h"
24
25 /* Return the root mountpoint of the file system on which FILE exists, in
26 malloced storage. FILE_STAT should be the result of stating FILE.
27 Give a diagnostic and return nullptr if unable to determine the mount point.
28 Exit if unable to restore current working directory. */
29 extern char *
find_mount_point(char const * file,struct stat const * file_stat)30 find_mount_point (char const *file, struct stat const *file_stat)
31 {
32 struct saved_cwd cwd;
33 struct stat last_stat;
34 char *mp = nullptr; /* The malloc'd mount point. */
35
36 if (save_cwd (&cwd) != 0)
37 {
38 error (0, errno, _("cannot get current directory"));
39 return nullptr;
40 }
41
42 if (S_ISDIR (file_stat->st_mode))
43 /* FILE is a directory, so just chdir there directly. */
44 {
45 last_stat = *file_stat;
46 if (chdir (file) < 0)
47 {
48 error (0, errno, _("cannot change to directory %s"), quoteaf (file));
49 return nullptr;
50 }
51 }
52 else
53 /* FILE is some other kind of file; use its directory. */
54 {
55 char *xdir = dir_name (file);
56 char *dir;
57 ASSIGN_STRDUPA (dir, xdir);
58 free (xdir);
59
60 if (chdir (dir) < 0)
61 {
62 error (0, errno, _("cannot change to directory %s"), quoteaf (dir));
63 return nullptr;
64 }
65
66 if (stat (".", &last_stat) < 0)
67 {
68 error (0, errno, _("cannot stat current directory (now %s)"),
69 quoteaf (dir));
70 goto done;
71 }
72 }
73
74 /* Now walk up FILE's parents until we find another file system or /,
75 chdiring as we go. LAST_STAT holds stat information for the last place
76 we visited. */
77 while (true)
78 {
79 struct stat st;
80 if (stat ("..", &st) < 0)
81 {
82 error (0, errno, _("cannot stat %s"), quoteaf (".."));
83 goto done;
84 }
85 if (st.st_dev != last_stat.st_dev || st.st_ino == last_stat.st_ino)
86 /* cwd is the mount point. */
87 break;
88 if (chdir ("..") < 0)
89 {
90 error (0, errno, _("cannot change to directory %s"), quoteaf (".."));
91 goto done;
92 }
93 last_stat = st;
94 }
95
96 /* Finally reached a mount point, see what it's called. */
97 mp = xgetcwd ();
98
99 done:
100 /* Restore the original cwd. */
101 {
102 int save_errno = errno;
103 if (restore_cwd (&cwd) != 0)
104 error (EXIT_FAILURE, errno,
105 _("failed to return to initial working directory"));
106 free_cwd (&cwd);
107 errno = save_errno;
108 }
109
110 return mp;
111 }
112