| /* Copyright (C) 2005-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library 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 |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <errno.h> |
| #include <fcntl.h> |
| #include <stddef.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <sysdep.h> |
| #include <unistd.h> |
| #include <kernel-features.h> |
| |
| |
| /* Read the contents of the symbolic link PATH relative to FD into no |
| more than LEN bytes of BUF. */ |
| ssize_t |
| readlinkat (fd, path, buf, len) |
| int fd; |
| const char *path; |
| char *buf; |
| size_t len; |
| { |
| int result; |
| |
| #ifdef __NR_readlinkat |
| # ifndef __ASSUME_ATFCTS |
| if (__have_atfcts >= 0) |
| # endif |
| { |
| result = INLINE_SYSCALL (readlinkat, 4, fd, path, buf, len); |
| # ifndef __ASSUME_ATFCTS |
| if (result == -1 && errno == ENOSYS) |
| __have_atfcts = -1; |
| else |
| # endif |
| return result; |
| } |
| #endif |
| |
| #ifndef __ASSUME_ATFCTS |
| char *pathbuf = NULL; |
| |
| if (fd != AT_FDCWD && path[0] != '/') |
| { |
| size_t pathlen = strlen (path); |
| if (__builtin_expect (pathlen == 0, 0)) |
| { |
| __set_errno (ENOENT); |
| return -1; |
| } |
| |
| static const char procfd[] = "/proc/self/fd/%d/%s"; |
| /* Buffer for the path name we are going to use. It consists of |
| - the string /proc/self/fd/ |
| - the file descriptor number |
| - the file name provided. |
| The final NUL is included in the sizeof. A bit of overhead |
| due to the format elements compensates for possible negative |
| numbers. */ |
| size_t buflen = sizeof (procfd) + sizeof (int) * 3 + pathlen; |
| pathbuf = __alloca (buflen); |
| |
| __snprintf (pathbuf, buflen, procfd, fd, path); |
| path = pathbuf; |
| } |
| |
| INTERNAL_SYSCALL_DECL (err); |
| |
| result = INTERNAL_SYSCALL (readlink, err, 3, path, buf, len); |
| |
| if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0)) |
| { |
| __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, pathbuf); |
| result = -1; |
| } |
| |
| return result; |
| #endif |
| } |
| libc_hidden_def (readlinkat) |