1 /* readlink wrapper to return the link name in malloc'd storage.
2 Unlike xreadlink and xreadlink_with_size, don't ever call exit.
4 Copyright (C) 2001, 2003-2007 Free Software Foundation, Inc.
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; see the file COPYING.
18 If not, write to the Free Software Foundation,
19 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
21 /* Written by Jim Meyering <jim@meyering.net> */
25 #include "mreadlink.h"
30 #include <sys/types.h>
35 # define SIZE_MAX ((size_t) -1)
38 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
41 /* SYMLINK_MAX is used only for an initial memory-allocation sanity
42 check, so it's OK to guess too small on hosts where there is no
43 arbitrary limit to symbolic link length. */
45 # define SYMLINK_MAX 1024
48 #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
50 /* Call readlink to get the symbolic link value of FILE.
51 SIZE is a hint as to how long the link is expected to be;
52 typically it is taken from st_size. It need not be correct.
53 Return a pointer to that NUL-terminated string in malloc'd storage.
54 If readlink fails, malloc fails, or if the link value is longer
55 than SSIZE_MAX, return NULL (caller may use errno to diagnose). */
58 mreadlink_with_size (char const *file, size_t size)
60 /* Some buggy file systems report garbage in st_size. Defend
61 against them by ignoring outlandish st_size values in the initial
63 size_t symlink_max = SYMLINK_MAX;
64 size_t INITIAL_LIMIT_BOUND = 8 * 1024;
65 size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
67 : INITIAL_LIMIT_BOUND);
69 /* The initial buffer size for the link value. */
70 size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
76 char *buffer = malloc (buf_size);
80 r = readlink (file, buffer, buf_size);
83 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
84 with errno == ERANGE if the buffer is too small. */
85 if (r < 0 && errno != ERANGE)
87 int saved_errno = errno;
93 if (link_length < buf_size)
95 buffer[link_length] = 0;
100 if (buf_size <= MAXSIZE / 2)
102 else if (buf_size < MAXSIZE)