sysdeps/unix/sysv/linux/symlinkat.c

   1 /* Copyright (C) 2005-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <stddef.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sysdep.h>
  25 #include <unistd.h>
  26 #include <kernel-features.h>
  27
  28
  29 /* Make a symbolic link to FROM named TO relative to TOFD.  */
  30 int
  31 symlinkat (from, tofd, to)
  32      const char *from;
  33      int tofd;
  34      const char *to;
  35 {
  36   int result;
  37
  38 #ifdef __NR_symlinkat
  39 # ifndef __ASSUME_ATFCTS
  40   if (__have_atfcts >= 0)
  41 # endif
  42     {
  43       result = INLINE_SYSCALL (symlinkat, 3, from, tofd, to);
  44 # ifndef __ASSUME_ATFCTS
  45       if (result == -1 && errno == ENOSYS)
  46         __have_atfcts = -1;
  47       else
  48 # endif
  49         return result;
  50     }
  51 #endif
  52
  53 #ifndef __ASSUME_ATFCTS
  54   char *buf = NULL;
  55
  56   if (tofd != AT_FDCWD && to[0] != '/')
  57     {
  58       size_t tolen = strlen (to);
  59       if (__glibc_unlikely (tolen == 0))
  60         {
  61           __set_errno (ENOENT);
  62           return -1;
  63         }
  64
  65       static const char procfd[] = "/proc/self/fd/%d/%s";
  66       /* Buffer for the path name we are going to use.  It consists of
  67          - the string /proc/self/fd/
  68          - the file descriptor number
  69          - the file name provided.
  70          The final NUL is included in the sizeof.   A bit of overhead
  71          due to the format elements compensates for possible negative
  72          numbers.  */
  73       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + tolen;
  74       buf = __alloca (buflen);
  75
  76       __snprintf (buf, buflen, procfd, tofd, to);
  77       to = buf;
  78     }
  79
  80   INTERNAL_SYSCALL_DECL (err);
  81
  82   result = INTERNAL_SYSCALL (symlink, err, 2, from, to);
  83
  84   if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
  85     {
  86       __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), tofd, buf);
  87       result = -1;
  88     }
  89
  90   return result;
  91 #endif
  92 }