sysdeps/posix/posix_fallocate.c

   1 /* Copyright (C) 2000, 2003, 2005 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 <unistd.h>
  22 #include <sys/stat.h>
  23 #include <sys/statfs.h>
  24
  25 /* Reserve storage for the data of the file associated with FD.  */
  26
  27 int
  28 posix_fallocate (int fd, __off_t offset, __off_t len)
  29 {
  30   struct stat64 st;
  31   struct statfs f;
  32
  33   /* `off_t' is a signed type.  Therefore we can determine whether
  34      OFFSET + LEN is too large if it is a negative value.  */
  35   if (offset < 0 || len < 0)
  36     return EINVAL;
  37   if (offset + len < 0)
  38     return EFBIG;
  39
  40   /* First thing we have to make sure is that this is really a regular
  41      file.  */
  42   if (__fxstat64 (_STAT_VER, fd, &st) != 0)
  43     return EBADF;
  44   if (S_ISFIFO (st.st_mode))
  45     return ESPIPE;
  46   if (! S_ISREG (st.st_mode))
  47     return ENODEV;
  48
  49   if (len == 0)
  50     {
  51       if (st.st_size < offset)
  52         {
  53           int ret = __ftruncate (fd, offset);
  54
  55           if (ret != 0)
  56             ret = errno;
  57           return ret;
  58         }
  59       return 0;
  60     }
  61
  62   /* We have to know the block size of the filesystem to get at least some
  63      sort of performance.  */
  64   if (__fstatfs (fd, &f) != 0)
  65     return errno;
  66
  67   /* Try to play safe.  */
  68   if (f.f_bsize == 0)
  69     f.f_bsize = 512;
  70
  71   /* Write something to every block.  */
  72   for (offset += (len - 1) % f.f_bsize; len > 0; offset += f.f_bsize)
  73     {
  74       len -= f.f_bsize;
  75
  76       if (offset < st.st_size)
  77         {
  78           unsigned char c;
  79           ssize_t rsize = __pread (fd, &c, 1, offset);
  80
  81           if (rsize < 0)
  82             return errno;
  83           /* If there is a non-zero byte, the block must have been
  84              allocated already.  */
  85           else if (rsize == 1 && c != 0)
  86             continue;
  87         }
  88
  89       if (__pwrite (fd, "", 1, offset) != 1)
  90         return errno;
  91     }
  92
  93   return 0;
  94 }