1 /* readlinkat wrapper to return the link name in malloc'd storage.
2 Unlike xreadlinkat, only call exit on failure to change directory.
4 Copyright (C) 2001, 2003-2007, 2009-2015 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 3 of the License, or
9 (at your option) any later version.
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. If not, see <http://www.gnu.org/licenses/>. */
19 /* Written by Jim Meyering <jim@meyering.net>
20 and Eric Blake <ebb9@byu.net>. */
24 #include "areadlink.h"
35 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
38 /* SYMLINK_MAX is used only for an initial memory-allocation sanity
39 check, so it's OK to guess too small on hosts where there is no
40 arbitrary limit to symbolic link length. */
42 # define SYMLINK_MAX 1024
45 # define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
47 /* Call readlinkat to get the symbolic link value of FILE, relative to FD.
48 SIZE is a hint as to how long the link is expected to be;
49 typically it is taken from st_size. It need not be correct.
50 Return a pointer to that NUL-terminated string in malloc'd storage.
51 If readlinkat fails, malloc fails, or if the link value is longer
52 than SSIZE_MAX, return NULL (caller may use errno to diagnose).
53 However, failure to change directory during readlinkat will issue
54 a diagnostic and exit. */
57 areadlinkat_with_size (int fd, char const *file, size_t size)
59 /* Some buggy file systems report garbage in st_size. Defend
60 against them by ignoring outlandish st_size values in the initial
62 size_t symlink_max = SYMLINK_MAX;
63 size_t INITIAL_LIMIT_BOUND = 8 * 1024;
64 size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
66 : INITIAL_LIMIT_BOUND);
68 /* The initial buffer size for the link value. */
69 size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
75 char *buffer = malloc (buf_size);
79 r = readlinkat (fd, file, buffer, buf_size);
82 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
83 with errno == ERANGE if the buffer is too small. */
84 if (r < 0 && errno != ERANGE)
86 int saved_errno = errno;
92 if (link_length < buf_size)
94 buffer[link_length] = 0;
99 if (buf_size <= MAXSIZE / 2)
101 else if (buf_size < MAXSIZE)
111 #else /* !HAVE_READLINKAT */
114 /* It is more efficient to change directories only once and call
115 areadlink_with_size, rather than repeatedly call the replacement
118 # define AT_FUNC_NAME areadlinkat_with_size
119 # define AT_FUNC_F1 areadlink_with_size
120 # define AT_FUNC_POST_FILE_PARAM_DECLS , size_t size
121 # define AT_FUNC_POST_FILE_ARGS , size
122 # define AT_FUNC_RESULT char *
123 # define AT_FUNC_FAIL NULL
124 # include "at-func.c"
127 # undef AT_FUNC_POST_FILE_PARAM_DECLS
128 # undef AT_FUNC_POST_FILE_ARGS
129 # undef AT_FUNC_RESULT
132 #endif /* !HAVE_READLINKAT */