sysdeps/unix/sysv/linux/fchmodat.c

   1 /* Change the protections of file relative to open directory.  Linux version.
   2    Copyright (C) 2006 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <stddef.h>
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <sys/types.h>
  27 #include <alloca.h>
  28 #include <kernel-features.h>
  29 #include <sysdep.h>
  30
  31 int
  32 fchmodat (fd, file, mode, flag)
  33      int fd;
  34      const char *file;
  35      mode_t mode;
  36      int flag;
  37 {
  38   if (flag & ~AT_SYMLINK_NOFOLLOW)
  39     {
  40       __set_errno (EINVAL);
  41       return -1;
  42     }
  43 #ifndef __NR_lchmod             /* Linux so far has no lchmod syscall.  */
  44   if (flag & AT_SYMLINK_NOFOLLOW)
  45     {
  46       __set_errno (ENOTSUP);
  47       return -1;
  48     }
  49 #endif
  50
  51   int result;
  52
  53 #ifdef __NR_fchmodat
  54 # ifndef __ASSUME_ATFCTS
  55   if (__have_atfcts >= 0)
  56 # endif
  57     {
  58       result = INLINE_SYSCALL (fchmodat, 3, fd, file, mode);
  59 # ifndef __ASSUME_ATFCTS
  60       if (result == -1 && errno == ENOSYS)
  61         __have_atfcts = -1;
  62       else
  63 # endif
  64         return result;
  65     }
  66 #endif
  67
  68 #ifndef __ASSUME_ATFCTS
  69   char *buf = NULL;
  70
  71   if (fd != AT_FDCWD && file[0] != '/')
  72     {
  73       size_t filelen = strlen (file);
  74       static const char procfd[] = "/proc/self/fd/%d/%s";
  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       buf = alloca (buflen);
  84
  85       __snprintf (buf, buflen, procfd, fd, file);
  86       file = buf;
  87     }
  88
  89   INTERNAL_SYSCALL_DECL (err);
  90
  91 # ifdef __NR_lchmod
  92   if (flag & AT_SYMLINK_NOFOLLOW)
  93     result = INTERNAL_SYSCALL (lchmod, err, 2, file, mode);
  94   else
  95 # endif
  96     result = INTERNAL_SYSCALL (chmod, err, 2, file, mode);
  97
  98   if (__builtin_expect (INTERNAL_SYSCALL_ERROR_P (result, err), 0))
  99     {
 100       __atfct_seterrno (INTERNAL_SYSCALL_ERRNO (result, err), fd, buf);
 101       result = -1;
 102     }
 103
 104   return result;
 105 #endif
 106 }