sysdeps/unix/sysv/linux/symlinkat.c

   1 /* Copyright (C) 2005, 2006 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <stddef.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sysdep.h>
  26 #include <unistd.h>
  27 #include <kernel-features.h>
  28
  29
  30 /* Make a symbolic link to FROM named TO relative to TOFD.  */
  31 int
  32 symlinkat (from, tofd, to)
  33      const char *from;
  34      int tofd;
  35      const char *to;
  36 {
  37   int result;
  38
  39 #ifdef __NR_symlinkat
  40 # ifndef __ASSUME_ATFCTS
  41   if (__have_atfcts >= 0)
  42 # endif
  43     {
  44       result = INLINE_SYSCALL (symlinkat, 3, from, tofd, to);
  45 # ifndef __ASSUME_ATFCTS
  46       if (result == -1 && errno == ENOSYS)
  47         __have_atfcts = -1;
  48       else
  49 # endif
  50         return result;
  51     }
  52 #endif
  53
  54 #ifndef __ASSUME_ATFCTS
  55   char *buf = NULL;
  56
  57   if (tofd != AT_FDCWD && to[0] != '/')
  58     {
  59       size_t tolen = strlen (to);
  60       static const char procfd[] = "/proc/self/fd/%d/%s";
  61       /* Buffer for the path name we are going to use.  It consists of
  62          - the string /proc/self/fd/
  63          - the file descriptor number
  64          - the file name provided.
  65          The final NUL is included in the sizeof.   A bit of overhead
  66          due to the format elements compensates for possible negative
  67          numbers.  */
  68       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + tolen;
  69       buf = __alloca (buflen);
  70
  71       __snprintf (buf, buflen, procfd, tofd, to);
  72       to = buf;
  73     }
  74
  75   INTERNAL_SYSCALL_DECL (err);
  76
  77   result = INTERNAL_SYSCALL (symlink, err, 2, from, to);
  78
  79   if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
  80     {
  81       __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), tofd, buf);
  82       result = -1;
  83     }
  84
  85   return result;
  86 #endif
  87 }