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author | Paul Eggert <eggert@cs.ucla.edu> | 2011-04-05 09:52:32 -0700 |
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committer | Paul Eggert <eggert@cs.ucla.edu> | 2011-04-05 09:52:32 -0700 |
commit | 4266051ac3a82f0a3bdfcf73c7f566e007676a0c (patch) | |
tree | 5ec06f00b04a056dd9cc8fc66debcfc845568e0b /lib/careadlinkat.c | |
parent | eccf108c763da99625bbe6bf221a13508798ce1a (diff) | |
download | gnulib-4266051ac3a82f0a3bdfcf73c7f566e007676a0c.tar.gz |
areadlink, areadlinkat: rewrite in terms of careadlinkat
* lib/areadlink.c, lib/areadlinkat.c: Include careadlinkat.h
instead of errno.h, limits.h, stdint.h, stdlib.h, string.h, unistd.h.
(SSIZE_MAX, INITIAL_BUF_SIZE): Remove.
(malloc, realloc): Remove #undefs.
(areadlink, areadlinkat): Rewrite in terms of careadlinkat.
* modules/areadlink (Depends-on): Add careadlinkat. Remove
readlink, ssize_t, stdint, unistd.
* modules/areadlinkat (Depends-on): Add careadlinkat. Remove
areadlink, stdint.
careadlinkat: new module
* lib/allocator.h, lib/careadlinkat.h, lib/careadlinkat.c:
* modules/careadlinkat: New files, written by me with
a review and feedback from Ben Pfaff in
<http://lists.gnu.org/archive/html/bug-gnulib/2011-04/msg00008.html>.
Diffstat (limited to 'lib/careadlinkat.c')
-rw-r--r-- | lib/careadlinkat.c | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/lib/careadlinkat.c b/lib/careadlinkat.c new file mode 100644 index 0000000000..15ffe24c0f --- /dev/null +++ b/lib/careadlinkat.c @@ -0,0 +1,175 @@ +/* Read symbolic links into a buffer without size limitation, relative to fd. + + Copyright (C) 2001, 2003-2004, 2007, 2009-2011 Free Software Foundation, + Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +/* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ + +#include <config.h> + +#include "careadlinkat.h" + +#include "allocator.h" + +#include <errno.h> +#include <limits.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +/* Use the system functions, not the gnulib overrides, because this + module does not depend on GNU or POSIX semantics. */ +#undef malloc +#undef realloc + +/* Define this independently so that stdint.h is not a prerequisite. */ +#ifndef SIZE_MAX +# define SIZE_MAX ((size_t) -1) +#endif + +#ifndef SSIZE_MAX +# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) +#endif + +#if ! HAVE_READLINKAT +/* Ignore FD. Get the symbolic link value of FILENAME and put it into + BUFFER, with size BUFFER_SIZE. This function acts like readlink + but has readlinkat's signature. */ +ssize_t +careadlinkatcwd (int fd, char const *filename, char *buffer, + size_t buffer_size) +{ + (void) fd; + return readlink (filename, buffer, buffer_size); +} +#endif + +/* A standard allocator. For now, only careadlinkat needs this, but + perhaps it should be moved to the allocator module. */ +static struct allocator const standard_allocator = + { malloc, realloc, free, NULL }; + +/* Assuming the current directory is FD, get the symbolic link value + of FILENAME as a null-terminated string and put it into a buffer. + If FD is AT_FDCWD, FILENAME is interpreted relative to the current + working directory, as in openat. + + If the link is small enough to fit into BUFFER put it there. + BUFFER's size is BUFFER_SIZE, and BUFFER can be null + if BUFFER_SIZE is zero. + + If the link is not small, put it into a dynamically allocated + buffer managed by ALLOC. It is the caller's responsibility to free + the returned value if it is nonnull and is not BUFFER. A null + ALLOC stands for the standard allocator. + + The PREADLINKAT function specifies how to read links. + + If successful, return the buffer address; otherwise return NULL and + set errno. */ + +char * +careadlinkat (int fd, char const *filename, + char *buffer, size_t buffer_size, + struct allocator const *alloc, + ssize_t (*preadlinkat) (int, char const *, char *, size_t)) +{ + char *buf; + size_t buf_size; + size_t buf_size_max = + SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; + char stack_buf[1024]; + + if (! alloc) + alloc = &standard_allocator; + + if (! buffer_size) + { + /* Allocate the initial buffer on the stack. This way, in the + common case of a symlink of small size, we get away with a + single small malloc() instead of a big malloc() followed by a + shrinking realloc(). */ + buffer = stack_buf; + buffer_size = sizeof stack_buf; + } + + buf = buffer; + buf_size = buffer_size; + + do + { + /* Attempt to read the link into the current buffer. */ + ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); + size_t link_size; + if (link_length < 0) + { + /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 + with errno == ERANGE if the buffer is too small. */ + int readlinkat_errno = errno; + if (readlinkat_errno != ERANGE) + { + if (buf != buffer) + { + alloc->free (buf); + errno = readlinkat_errno; + } + return NULL; + } + } + + link_size = link_length; + + if (link_size < buf_size) + { + buf[link_size++] = '\0'; + + if (buf == stack_buf) + { + char *b = (char *) alloc->malloc (link_size); + if (! b) + break; + memcpy (b, buf, link_size); + buf = b; + } + else if (link_size < buf_size && buf != buffer && alloc->realloc) + { + /* Shrink BUF before returning it. */ + char *b = (char *) alloc->realloc (buf, link_size); + if (b) + buf = b; + } + + return buf; + } + + if (buf != buffer) + alloc->free (buf); + + if (buf_size <= buf_size_max / 2) + buf_size *= 2; + else if (buf_size < buf_size_max) + buf_size = buf_size_max; + else + break; + buf = (char *) alloc->malloc (buf_size); + } + while (buf); + + if (alloc->die) + alloc->die (); + errno = ENOMEM; + return NULL; +} |