lib/full-write.c

   1 /* An interface to read and write that retries (if necessary) until complete.
   2
   3    Copyright (C) 1993, 1994, 1997-2003 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software Foundation,
  17    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  18
  19 #if HAVE_CONFIG_H
  20 # include <config.h>
  21 #endif
  22
  23 #include <errno.h>
  24 #ifndef errno
  25 extern int errno;
  26 #endif
  27
  28 #ifdef FULL_READ
  29 # include "full-read.h"
  30 # include "safe-read.h"
  31 # define safe_rw safe_read
  32 # define full_rw full_read
  33 # undef const
  34 # define const /* empty */
  35 #else
  36 # include "full-write.h"
  37 # include "safe-write.h"
  38 # define safe_rw safe_write
  39 # define full_rw full_write
  40 #endif
  41
  42 #ifdef FULL_READ
  43 /* Set errno to zero upon EOF.  */
  44 # define ZERO_BYTE_TRANSFER_ERRNO 0
  45 #else
  46 /* Some buggy drivers return 0 when one tries to write beyond
  47    a device's end.  (Example: Linux 1.2.13 on /dev/fd0.)
  48    Set errno to ENOSPC so they get a sensible diagnostic.  */
  49 # define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
  50 #endif
  51
  52 /* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
  53    interrupted or if a partial write(read) occurs.  Return the number
  54    of bytes transferred.
  55    When writing, set errno if fewer than COUNT bytes are written.
  56    When reading, if fewer than COUNT bytes are read, you must examine
  57    errno to distinguish failure from EOF (errno == 0).  */
  58 size_t
  59 full_rw (int fd, const void *buf, size_t count)
  60 {
  61   size_t total = 0;
  62   const char *ptr = buf;
  63
  64   while (count > 0)
  65     {
  66       size_t n_rw = safe_rw (fd, ptr, count);
  67       if (n_rw == (size_t) -1)
  68         break;
  69       if (n_rw == 0)
  70         {
  71           errno = ZERO_BYTE_TRANSFER_ERRNO;
  72           break;
  73         }
  74       total += n_rw;
  75       ptr += n_rw;
  76       count -= n_rw;
  77     }
  78
  79   return total;
  80 }