sysdeps/unix/sysv/linux/linkat.c

   1 /* Copyright (C) 2005, 2006, 2009 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 <string.h>
  22 #include <stdio.h>
  23 #include <sysdep.h>
  24 #include <unistd.h>
  25 #include <kernel-features.h>
  26
  27
  28 /* Make a link to FROM named TO but relative paths in TO and FROM are
  29    interpreted relative to FROMFD and TOFD respectively.  */
  30 int
  31 linkat (fromfd, from, tofd, to, flags)
  32      int fromfd;
  33      const char *from;
  34      int tofd;
  35      const char *to;
  36      int flags;
  37 {
  38   int result;
  39
  40 #ifdef __NR_linkat
  41 # ifndef __ASSUME_ATFCTS
  42   if (__have_atfcts >= 0)
  43 # endif
  44     {
  45       result = INLINE_SYSCALL (linkat, 5, fromfd, from, tofd, to, flags);
  46 # ifndef __ASSUME_ATFCTS
  47       if (result == -1 && errno == ENOSYS)
  48         __have_atfcts = -1;
  49       else
  50 # endif
  51         return result;
  52     }
  53 #endif
  54
  55 #ifndef __ASSUME_ATFCTS
  56   /* Without kernel support we cannot handle AT_SYMLINK_FOLLOW.  */
  57   if (flags != 0)
  58     {
  59       __set_errno (EINVAL);
  60       return -1;
  61     }
  62
  63   static const char procfd[] = "/proc/self/fd/%d/%s";
  64   char *buffrom = NULL;
  65
  66   if (fromfd != AT_FDCWD && from[0] != '/')
  67     {
  68       size_t filelen = strlen (from);
  69       if (__builtin_expect (filelen == 0, 0))
  70         {
  71           __set_errno (ENOENT);
  72           return -1;
  73         }
  74
  75       /* Buffer for the path name we are going to use.  It consists of
  76          - the string /proc/self/fd/
  77          - the file descriptor number
  78          - the file name provided.
  79          The final NUL is included in the sizeof.   A bit of overhead
  80          due to the format elements compensates for possible negative
  81          numbers.  */
  82       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
  83       buffrom = alloca (buflen);
  84
  85       __snprintf (buffrom, buflen, procfd, fromfd, from);
  86       from = buffrom;
  87     }
  88
  89   char *bufto = NULL;
  90
  91   if (tofd != AT_FDCWD && to[0] != '/')
  92     {
  93       size_t filelen = strlen (to);
  94       /* Buffer for the path name we are going to use.  It consists of
  95          - the string /proc/self/fd/
  96          - the file descriptor number
  97          - the file name provided.
  98          The final NUL is included in the sizeof.   A bit of overhead
  99          due to the format elements compensates for possible negative
 100          numbers.  */
 101       size_t buflen = sizeof (procfd) + sizeof (int) * 3 + filelen;
 102       bufto = alloca (buflen);
 103
 104       __snprintf (bufto, buflen, procfd, tofd, to);
 105       to = bufto;
 106     }
 107
 108   INTERNAL_SYSCALL_DECL (err);
 109
 110   result = INTERNAL_SYSCALL (link, err, 2, from,  to);
 111
 112   if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
 113     {
 114       __atfct_seterrno_2 (INTERNAL_SYSCALL_ERRNO (result, err), tofd, bufto,
 115                           fromfd, buffrom);
 116       result = -1;
 117     }
 118
 119   return result;
 120 #endif
 121 }