sysdeps/posix/posix_fallocate.c

   1 /* Copyright (C) 2000-2015 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 <unistd.h>
  21 #include <sys/stat.h>
  22 #include <sys/statfs.h>
  23
  24 /* Reserve storage for the data of the file associated with FD.  */
  25
  26 int
  27 posix_fallocate (int fd, __off_t offset, __off_t len)
  28 {
  29   struct stat64 st;
  30   struct statfs f;
  31
  32   /* `off_t' is a signed type.  Therefore we can determine whether
  33      OFFSET + LEN is too large if it is a negative value.  */
  34   if (offset < 0 || len < 0)
  35     return EINVAL;
  36   if (offset + len < 0)
  37     return EFBIG;
  38
  39   /* First thing we have to make sure is that this is really a regular
  40      file.  */
  41   if (__fxstat64 (_STAT_VER, fd, &st) != 0)
  42     return EBADF;
  43   if (S_ISFIFO (st.st_mode))
  44     return ESPIPE;
  45   if (! S_ISREG (st.st_mode))
  46     return ENODEV;
  47
  48   if (len == 0)
  49     {
  50       if (st.st_size < offset)
  51         {
  52           int ret = __ftruncate (fd, offset);
  53
  54           if (ret != 0)
  55             ret = errno;
  56           return ret;
  57         }
  58       return 0;
  59     }
  60
  61   /* We have to know the block size of the filesystem to get at least some
  62      sort of performance.  */
  63   if (__fstatfs (fd, &f) != 0)
  64     return errno;
  65
  66   /* Try to play safe.  */
  67   if (f.f_bsize == 0)
  68     f.f_bsize = 512;
  69
  70   /* Write something to every block.  */
  71   for (offset += (len - 1) % f.f_bsize; len > 0; offset += f.f_bsize)
  72     {
  73       len -= f.f_bsize;
  74
  75       if (offset < st.st_size)
  76         {
  77           unsigned char c;
  78           ssize_t rsize = __pread (fd, &c, 1, offset);
  79
  80           if (rsize < 0)
  81             return errno;
  82           /* If there is a non-zero byte, the block must have been
  83              allocated already.  */
  84           else if (rsize == 1 && c != 0)
  85             continue;
  86         }
  87
  88       if (__pwrite (fd, "", 1, offset) != 1)
  89         return errno;
  90     }
  91
  92   return 0;
  93 }