1 /* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
3 Copyright (C) 2001, 2003, 2004, 2005, 2006 Free Software
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 "xreadlink.h"
30 #include <sys/types.h>
35 # define SIZE_MAX ((size_t) -1)
38 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
41 #define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
45 /* Call readlink to get the symbolic link value of FILE.
46 SIZE is a hint as to how long the link is expected to be;
47 typically it is taken from st_size. It need not be correct.
48 Return a pointer to that NUL-terminated string in malloc'd storage.
49 If readlink fails, return NULL (caller may use errno to diagnose).
50 If malloc fails, or if the link value is longer than SSIZE_MAX :-),
51 give a diagnostic and exit. */
54 xreadlink (char const *file, size_t size)
56 /* The initial buffer size for the link value. A power of 2
57 detects arithmetic overflow earlier, but is not required. */
58 size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE;
62 char *buffer = xmalloc (buf_size);
63 ssize_t r = readlink (file, buffer, buf_size);
64 size_t link_length = r;
66 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
67 with errno == ERANGE if the buffer is too small. */
68 if (r < 0 && errno != ERANGE)
70 int saved_errno = errno;
76 if (link_length < buf_size)
78 buffer[link_length] = 0;
83 if (buf_size <= MAXSIZE / 2)
85 else if (buf_size < MAXSIZE)