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. */
21 #define _GL_USE_STDLIB_ALLOC 1
24 #include "careadlinkat.h"
26 #include "allocator.h"
34 /* Define this independently so that stdint.h is not a prerequisite. */
36 # define SIZE_MAX ((size_t) -1)
40 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
44 /* Ignore FD. Get the symbolic link value of FILENAME and put it into
45 BUFFER, with size BUFFER_SIZE. This function acts like readlink
46 but has readlinkat's signature. */
48 careadlinkatcwd (int fd, char const *filename, char *buffer,
52 return readlink (filename, buffer, buffer_size);
56 /* A standard allocator. For now, only careadlinkat needs this, but
57 perhaps it should be moved to the allocator module. */
58 static struct allocator const standard_allocator =
59 { malloc, realloc, free, NULL };
61 /* Assuming the current directory is FD, get the symbolic link value
62 of FILENAME as a null-terminated string and put it into a buffer.
63 If FD is AT_FDCWD, FILENAME is interpreted relative to the current
64 working directory, as in openat.
66 If the link is small enough to fit into BUFFER put it there.
67 BUFFER's size is BUFFER_SIZE, and BUFFER can be null
68 if BUFFER_SIZE is zero.
70 If the link is not small, put it into a dynamically allocated
71 buffer managed by ALLOC. It is the caller's responsibility to free
72 the returned value if it is nonnull and is not BUFFER. A null
73 ALLOC stands for the standard allocator.
75 The PREADLINKAT function specifies how to read links.
77 If successful, return the buffer address; otherwise return NULL and
81 careadlinkat (int fd, char const *filename,
82 char *buffer, size_t buffer_size,
83 struct allocator const *alloc,
84 ssize_t (*preadlinkat) (int, char const *, char *, size_t))
89 SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX;
93 alloc = &standard_allocator;
97 /* Allocate the initial buffer on the stack. This way, in the
98 common case of a symlink of small size, we get away with a
99 single small malloc() instead of a big malloc() followed by a
100 shrinking realloc(). */
102 buffer_size = sizeof stack_buf;
106 buf_size = buffer_size;
110 /* Attempt to read the link into the current buffer. */
111 ssize_t link_length = preadlinkat (fd, filename, buf, buf_size);
115 /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
116 with errno == ERANGE if the buffer is too small. */
117 int readlinkat_errno = errno;
118 if (readlinkat_errno != ERANGE)
123 errno = readlinkat_errno;
129 link_size = link_length;
131 if (link_size < buf_size)
133 buf[link_size++] = '\0';
135 if (buf == stack_buf)
137 char *b = (char *) alloc->allocate (link_size);
140 memcpy (b, buf, link_size);
143 else if (link_size < buf_size && buf != buffer && alloc->reallocate)
145 /* Shrink BUF before returning it. */
146 char *b = (char *) alloc->reallocate (buf, link_size);
157 if (buf_size <= buf_size_max / 2)
159 else if (buf_size < buf_size_max)
160 buf_size = buf_size_max;
163 buf = (char *) alloc->allocate (buf_size);