lib/full-write.c

   1 /* An interface to read and write that retries (if necessary) until complete.
   2
   3    Copyright (C) 1993-1994, 1997-2006, 2009-2021 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 3 of the License, or
   8    (at your option) 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, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 /* Specification.  */
  21 #ifdef FULL_READ
  22 # include "full-read.h"
  23 #else
  24 # include "full-write.h"
  25 #endif
  26
  27 #include <errno.h>
  28
  29 #ifdef FULL_READ
  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 "safe-write.h"
  37 # define safe_rw safe_write
  38 # define full_rw full_write
  39 #endif
  40
  41 #ifdef FULL_READ
  42 /* Set errno to zero upon EOF.  */
  43 # define ZERO_BYTE_TRANSFER_ERRNO 0
  44 #else
  45 /* Some buggy drivers return 0 when one tries to write beyond
  46    a device's end.  (Example: Linux 1.2.13 on /dev/fd0.)
  47    Set errno to ENOSPC so they get a sensible diagnostic.  */
  48 # define ZERO_BYTE_TRANSFER_ERRNO ENOSPC
  49 #endif
  50
  51 /* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
  52    interrupted or if a partial write(read) occurs.  Return the number
  53    of bytes transferred.
  54    When writing, set errno if fewer than COUNT bytes are written.
  55    When reading, if fewer than COUNT bytes are read, you must examine
  56    errno to distinguish failure from EOF (errno == 0).  */
  57 size_t
  58 full_rw (int fd, const void *buf, size_t count)
  59 {
  60   size_t total = 0;
  61   const char *ptr = (const char *) buf;
  62
  63   while (count > 0)
  64     {
  65       size_t n_rw = safe_rw (fd, ptr, count);
  66       if (n_rw == (size_t) -1)
  67         break;
  68       if (n_rw == 0)
  69         {
  70           errno = ZERO_BYTE_TRANSFER_ERRNO;
  71           break;
  72         }
  73       total += n_rw;
  74       ptr += n_rw;
  75       count -= n_rw;
  76     }
  77
  78   return total;
  79 }