Merge from origin/emacs-24
[emacs.git] / lib / openat-proc.c
blob4e1d34198529865caa84bf2596cad9779acfe70b
1 /* Create /proc/self/fd-related names for subfiles of open directories.
3 Copyright (C) 2006, 2009-2015 Free Software Foundation, Inc.
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.
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.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert. */
20 #include <config.h>
22 #include "openat-priv.h"
24 #include <sys/types.h>
25 #include <sys/stat.h>
26 #include <fcntl.h>
28 #include <stdio.h>
29 #include <stdlib.h>
30 #include <string.h>
31 #include <unistd.h>
33 #include "intprops.h"
35 #define PROC_SELF_FD_FORMAT "/proc/self/fd/%d/%s"
37 #define PROC_SELF_FD_NAME_SIZE_BOUND(len) \
38 (sizeof PROC_SELF_FD_FORMAT - sizeof "%d%s" \
39 + INT_STRLEN_BOUND (int) + (len) + 1)
42 /* Set BUF to the expansion of PROC_SELF_FD_FORMAT, using FD and FILE
43 respectively for %d and %s. If successful, return BUF if the
44 result fits in BUF, dynamically allocated memory otherwise. But
45 return NULL if /proc is not reliable, either because the operating
46 system support is lacking or because memory is low. */
47 char *
48 openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file)
50 static int proc_status = 0;
52 /* Make sure the caller gets ENOENT when appropriate. */
53 if (!*file)
55 buf[0] = '\0';
56 return buf;
59 if (! proc_status)
61 /* Set PROC_STATUS to a positive value if /proc/self/fd is
62 reliable, and a negative value otherwise. Solaris 10
63 /proc/self/fd mishandles "..", and any file name might expand
64 to ".." after symbolic link expansion, so avoid /proc/self/fd
65 if it mishandles "..". Solaris 10 has openat, but this
66 problem is exhibited on code that built on Solaris 8 and
67 running on Solaris 10. */
69 int proc_self_fd = open ("/proc/self/fd",
70 O_SEARCH | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
71 if (proc_self_fd < 0)
72 proc_status = -1;
73 else
75 /* Detect whether /proc/self/fd/%i/../fd exists, where %i is the
76 number of a file descriptor open on /proc/self/fd. On Linux,
77 that name resolves to /proc/self/fd, which was opened above.
78 However, on Solaris, it may resolve to /proc/self/fd/fd, which
79 cannot exist, since all names in /proc/self/fd are numeric. */
80 char dotdot_buf[PROC_SELF_FD_NAME_SIZE_BOUND (sizeof "../fd" - 1)];
81 sprintf (dotdot_buf, PROC_SELF_FD_FORMAT, proc_self_fd, "../fd");
82 proc_status = access (dotdot_buf, F_OK) ? -1 : 1;
83 close (proc_self_fd);
87 if (proc_status < 0)
88 return NULL;
89 else
91 size_t bufsize = PROC_SELF_FD_NAME_SIZE_BOUND (strlen (file));
92 char *result = buf;
93 if (OPENAT_BUFFER_SIZE < bufsize)
95 result = malloc (bufsize);
96 if (! result)
97 return NULL;
99 sprintf (result, PROC_SELF_FD_FORMAT, fd, file);
100 return result;