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Orthogonal approach to read()/write() that handles EINTR and counts > 2^31 correctly.
author Bruno Haible <bruno@clisp.org>
date Fri, 22 Nov 2002 16:25:53 +0000
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children 6a1238f585b1
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4002
9fcf64c770ed Orthogonal approach to read()/write() that handles EINTR and counts > 2^31
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1 /* An interface to write() that retries after interrupts.
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2 Copyright (C) 1993, 1994, 1998, 2002 Free Software Foundation, Inc.
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3
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4 This program is free software; you can redistribute it and/or modify
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5 it under the terms of the GNU General Public License as published by
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6 the Free Software Foundation; either version 2, or (at your option)
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7 any later version.
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8
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9 This program is distributed in the hope that it will be useful,
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10 but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 GNU General Public License for more details.
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13
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14 You should have received a copy of the GNU General Public License
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15 along with this program; if not, write to the Free Software Foundation,
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16 Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
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17
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18 #if HAVE_CONFIG_H
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19 # include <config.h>
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20 #endif
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21
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22 /* Specification. */
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23 #include "safe-write.h"
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24
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25 /* Get ssize_t. */
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26 #include <sys/types.h>
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27 #if HAVE_UNISTD_H
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28 # include <unistd.h>
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29 #endif
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30
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31 #include <errno.h>
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32 #ifndef errno
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33 extern int errno;
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34 #endif
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35
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36 #include <limits.h>
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37
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38 /* We don't pass an nbytes count > SSIZE_MAX to write() - POSIX says the
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39 effect would be implementation-defined. Also we don't pass an nbytes
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40 count > INT_MAX but <= SSIZE_MAX to write() - this triggers a bug in
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41 Tru64 5.1. */
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42 #define MAX_BYTES_TO_READ INT_MAX
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43
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44 /* Write up to COUNT bytes at BUF to descriptor FD, retrying if interrupted.
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45 Return the actual number of bytes written, zero for EOF, or (size_t) -1
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46 for an error. */
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47 size_t
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48 safe_write (int fd, const void *buf, size_t count)
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49 {
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50 size_t total_written = 0;
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51
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52 if (count > 0)
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53 {
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54 const char *ptr = (const char *) buf;
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55 do
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56 {
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57 size_t nbytes_to_write = count;
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58 ssize_t result;
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59
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60 /* Limit the number of bytes to write in one round, to avoid running
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61 into unspecified behaviour. But keep the file pointer block
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62 aligned when doing so. */
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63 if (nbytes_to_write > MAX_BYTES_TO_READ)
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64 nbytes_to_write = MAX_BYTES_TO_READ & ~8191;
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65
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66 result = write (fd, ptr, nbytes_to_write);
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67 if (result < 0)
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68 {
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69 #ifdef EINTR
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70 if (errno == EINTR)
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71 continue;
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72 #endif
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73 return result;
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74 }
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75 total_written += result;
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76 ptr += result;
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77 count -= result;
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78 }
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79 while (count > 0);
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80 }
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81
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82 return total_written;
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83 }