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