Dogcows Code - chaz/tar/blob - 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 /* Specification.  */
  24 #ifdef FULL_READ
  25 # include "full-read.h"
  26 #else
  27 # include "full-write.h"
  28 #endif
  29
  30 #include <errno.h>
  31 #ifndef errno
  32 extern int errno;
  33 #endif
  34
  35 #ifdef FULL_READ
  36 # include "safe-read.h"
  37 # define safe_rw safe_read
  38 # define full_rw full_read
  39 # undef const
  40 # define const /* empty */
  41 #else
  42 # include "safe-write.h"
  43 # define safe_rw safe_write
  44 # define full_rw full_write
  45 #endif
  46
  47 #ifdef FULL_READ
  48 /* Set errno to zero upon EOF.  */
  49 # define ZERO_BYTE_TRANSFER_ERRNO 0
  50 #else
  51 /* Some buggy drivers return 0 when one tries to write beyond
  52    a device's end.  (Example: Linux 1.2.13 on /dev/fd0.)
  53    Set errno to ENOSPC so they get a sensible diagnostic.  */
  54 # define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
  55 #endif
  56
  57 /* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
  58    interrupted or if a partial write(read) occurs.  Return the number
  59    of bytes transferred.
  60    When writing, set errno if fewer than COUNT bytes are written.
  61    When reading, if fewer than COUNT bytes are read, you must examine
  62    errno to distinguish failure from EOF (errno == 0).  */
  63 size_t
  64 full_rw (int fd, const void *buf, size_t count)
  65 {
  66   size_t total = 0;
  67   const char *ptr = buf;
  68
  69   while (count > 0)
  70     {
  71       size_t n_rw = safe_rw (fd, ptr, count);
  72       if (n_rw == (size_t) -1)
  73         break;
  74       if (n_rw == 0)
  75         {
  76           errno = ZERO_BYTE_TRANSFER_ERRNO;
  77           break;
  78         }
  79       total += n_rw;
  80       ptr += n_rw;
  81       count -= n_rw;
  82     }
  83
  84   return total;
  85 }