lib/safe-read.c

   1 /* An interface to read and write that retries after interrupts.
   2
   3    Copyright (C) 1993-1994, 1998, 2002-2006, 2009-2017 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #ifdef SAFE_WRITE
  23 # include "safe-write.h"
  24 #else
  25 # include "safe-read.h"
  26 #endif
  27
  28 /* Get ssize_t.  */
  29 #include <sys/types.h>
  30 #include <unistd.h>
  31
  32 #include <errno.h>
  33
  34 #ifdef EINTR
  35 # define IS_EINTR(x) ((x) == EINTR)
  36 #else
  37 # define IS_EINTR(x) 0
  38 #endif
  39
  40 #include <limits.h>
  41
  42 #ifdef SAFE_WRITE
  43 # define safe_rw safe_write
  44 # define rw write
  45 #else
  46 # define safe_rw safe_read
  47 # define rw read
  48 # undef const
  49 # define const /* empty */
  50 #endif
  51
  52 /* Read(write) up to COUNT bytes at BUF from(to) descriptor FD, retrying if
  53    interrupted.  Return the actual number of bytes read(written), zero for EOF,
  54    or SAFE_READ_ERROR(SAFE_WRITE_ERROR) upon error.  */
  55 size_t
  56 safe_rw (int fd, void const *buf, size_t count)
  57 {
  58   /* Work around a bug in Tru64 5.1.  Attempting to read more than
  59      INT_MAX bytes fails with errno == EINVAL.  See
  60      <http://lists.gnu.org/archive/html/bug-gnu-utils/2002-04/msg00010.html>.
  61      When decreasing COUNT, keep it block-aligned.  */
  62   enum { BUGGY_READ_MAXIMUM = INT_MAX & ~8191 };
  63
  64   for (;;)
  65     {
  66       ssize_t result = rw (fd, buf, count);
  67
  68       if (0 <= result)
  69         return result;
  70       else if (IS_EINTR (errno))
  71         continue;
  72       else if (errno == EINVAL && BUGGY_READ_MAXIMUM < count)
  73         count = BUGGY_READ_MAXIMUM;
  74       else
  75         return result;
  76     }
  77 }