1 /* Make a file's ancestor directories.
2
3 Copyright (C) 2006, 2009-2023 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Paul Eggert. */
19
20 #include <config.h>
21
22 #include "mkancesdirs.h"
23
24 #include <sys/types.h>
25 #include <sys/stat.h>
26 #include <fcntl.h>
27
28 #include <errno.h>
29 #include <unistd.h>
30
31 #include "filename.h"
32 #include "savewd.h"
33
34 /* Ensure that the ancestor directories of FILE exist, using an
35 algorithm that should work even if two processes execute this
36 function in parallel. Modify FILE as necessary to access the
37 ancestor directories, but restore FILE to an equivalent value
38 if successful.
39
40 WD points to the working directory, using the conventions of
41 savewd.
42
43 Create any ancestor directories that don't already exist, by
44 invoking MAKE_DIR (FILE, COMPONENT, MAKE_DIR_ARG). This function
45 should return 0 if successful, -1 (setting errno) otherwise. If
46 COMPONENT is relative, it is relative to the temporary working
47 directory, which may differ from *WD.
48
49 Ordinarily MAKE_DIR is executed with the working directory changed
50 to reflect the already-made prefix, and mkancesdirs returns with
51 the working directory changed a prefix of FILE. However, if the
52 initial working directory cannot be saved in a file descriptor,
53 MAKE_DIR is invoked in a subprocess and this function returns in
54 both the parent and child process, so the caller should not assume
55 any changed state survives other than the EXITMAX component of WD,
56 and the caller should take care that the parent does not attempt to
57 do the work that the child is doing.
58
59 If successful and if this process can go ahead and create FILE,
60 return the length of the prefix of FILE that has already been made.
61 If successful so far but a child process is doing the actual work,
62 return -2. If unsuccessful, return -1 and set errno. */
63
64 ptrdiff_t
65 mkancesdirs (char *file, struct savewd *wd,
66 int (*make_dir) (char const *, char const *, void *),
67 void *make_dir_arg)
68 {
69 /* Address of the previous directory separator that follows an
70 ordinary byte in a file name in the left-to-right scan, or NULL
71 if no such separator precedes the current location P. */
72 char *sep = NULL;
73
74 /* Address of the leftmost file name component that has not yet
75 been processed. */
76 char *component = file;
77
78 char *p = file + FILE_SYSTEM_PREFIX_LEN (file);
79 char c;
80 bool made_dir = false;
81
82 /* Scan forward through FILE, creating and chdiring into directories
83 along the way. Try MAKE_DIR before chdir, so that the procedure
84 works even when two or more processes are executing it in
85 parallel. Isolate each file name component by having COMPONENT
86 point to its start and SEP point just after its end. */
87
88 while ((c = *p++))
89 if (ISSLASH (*p))
90 {
91 if (! ISSLASH (c))
92 sep = p;
93 }
94 else if (ISSLASH (c) && *p && sep)
95 {
96 /* Don't bother to make or test for "." since it does not
97 affect the algorithm. */
98 if (! (sep - component == 1 && component[0] == '.'))
99 {
100 int make_dir_errno = 0;
101 int savewd_chdir_options = 0;
102 int chdir_result;
103
104 /* Temporarily modify FILE to isolate this file name
105 component. */
106 *sep = '\0';
107
108 /* Invoke MAKE_DIR on this component, except don't bother
109 with ".." since it must exist if its "parent" does. */
110 if (sep - component == 2
111 && component[0] == '.' && component[1] == '.')
112 made_dir = false;
113 else if (make_dir (file, component, make_dir_arg) < 0)
114 make_dir_errno = errno;
115 else
116 made_dir = true;
117
118 if (made_dir)
119 savewd_chdir_options |= SAVEWD_CHDIR_NOFOLLOW;
120
121 chdir_result =
122 savewd_chdir (wd, component, savewd_chdir_options, NULL);
123
124 /* Undo the temporary modification to FILE, unless there
125 was a failure. */
126 if (chdir_result != -1)
127 *sep = '/';
128
129 if (chdir_result != 0)
130 {
131 if (make_dir_errno != 0 && errno == ENOENT)
132 errno = make_dir_errno;
133 return chdir_result;
134 }
135 }
136
137 component = p;
138 }
139
140 return component - file;
141 }