1 /* Read symbolic links into a buffer without size limitation, relative to fd.
3 Copyright (C) 2001, 2003-2004, 2007, 2009-2011 Free Software Foundation,
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 Paul Eggert, Bruno Haible, and Jim Meyering. */
23 #include "careadlinkat.h"
30 /* Define this independently so that stdint.h is not a prerequisite. */
32 # define SIZE_MAX ((size_t) -1)
36 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
39 #include "allocator.h"
42 /* Ignore FD. Get the symbolic link value of FILENAME and put it into
43 BUFFER, with size BUFFER_SIZE. This function acts like readlink
44 but has readlinkat's signature. */
46 careadlinkatcwd (int fd, char const *filename, char *buffer,
50 return readlink (filename, buffer, buffer_size);
54 /* Assuming the current directory is FD, get the symbolic link value
55 of FILENAME as a null-terminated string and put it into a buffer.
56 If FD is AT_FDCWD, FILENAME is interpreted relative to the current
57 working directory, as in openat.
59 If the link is small enough to fit into BUFFER put it there.
60 BUFFER's size is BUFFER_SIZE, and BUFFER can be null
61 if BUFFER_SIZE is zero.
63 If the link is not small, put it into a dynamically allocated
64 buffer managed by ALLOC. It is the caller's responsibility to free
65 the returned value if it is nonnull and is not BUFFER. A null
66 ALLOC stands for the standard allocator.
68 The PREADLINKAT function specifies how to read links. It operates
69 like POSIX readlinkat()
70 <http://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html>
71 but can assume that its first argument is the same as FD.
73 If successful, return the buffer address; otherwise return NULL and
77 careadlinkat (int fd, char const *filename,
78 char *buffer, size_t buffer_size,
79 struct allocator const *alloc,
80 ssize_t (*preadlinkat) (int, char const *, char *, size_t))
85 SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX;
89 alloc = &stdlib_allocator;
93 /* Allocate the initial buffer on the stack. This way, in the
94 common case of a symlink of small size, we get away with a
95 single small malloc() instead of a big malloc() followed by a
96 shrinking realloc(). */
98 buffer_size = sizeof stack_buf;
102 buf_size = buffer_size;
106 /* Attempt to read the link into the current buffer. */
107 ssize_t link_length = preadlinkat (fd, filename, buf, buf_size);
111 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
112 with errno == ERANGE if the buffer is too small. */
113 int readlinkat_errno = errno;
114 if (readlinkat_errno != ERANGE)
119 errno = readlinkat_errno;
125 link_size = link_length;
127 if (link_size < buf_size)
129 buf[link_size++] = '\0';
131 if (buf == stack_buf)
133 char *b = (char *) alloc->allocate (link_size);
136 memcpy (b, buf, link_size);
139 else if (link_size < buf_size && buf != buffer && alloc->reallocate)
141 /* Shrink BUF before returning it. */
142 char *b = (char *) alloc->reallocate (buf, link_size);
153 if (buf_size <= buf_size_max / 2)
155 else if (buf_size < buf_size_max)
156 buf_size = buf_size_max;
159 buf = (char *) alloc->allocate (buf_size);