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annotate lib/getdtablesize.c @ 17907:0a1c2535cad9

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euidaccess: Fix Android build * modules/euidaccess (Depends-on): Add fcntl-h to ensure that AT_EACCESS gets declared.
author Kevin Cernekee <cernekee@google.com>
date Wed, 11 Feb 2015 15:22:54 -0800
parents ab58d4870664
children c513a8c0f555
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1 /* getdtablesize() function for platforms that don't have it.
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2 Copyright (C) 2008-2015 Free Software Foundation, Inc.
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3 Written by Bruno Haible <bruno@clisp.org>, 2008.
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4
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5 This program is free software: you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 3 of the License, or
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8 (at your option) any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
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17
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18 #include <config.h>
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19
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20 /* Specification. */
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21 #include <unistd.h>
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22
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23 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
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24
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25 # include <stdio.h>
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26
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27 # include "msvc-inval.h"
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28
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29 # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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30 static int
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31 _setmaxstdio_nothrow (int newmax)
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32 {
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33 int result;
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34
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35 TRY_MSVC_INVAL
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36 {
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37 result = _setmaxstdio (newmax);
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38 }
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39 CATCH_MSVC_INVAL
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40 {
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41 result = -1;
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42 }
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43 DONE_MSVC_INVAL;
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44
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45 return result;
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46 }
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47 # define _setmaxstdio _setmaxstdio_nothrow
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48 # endif
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49
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50 /* Cache for the previous getdtablesize () result. Safe to cache because
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51 Windows also lacks setrlimit. */
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52 static int dtablesize;
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53
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54 int
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55 getdtablesize (void)
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56 {
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57 if (dtablesize == 0)
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58 {
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59 /* We are looking for the number N such that the valid file descriptors
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60 are 0..N-1. It can be obtained through a loop as follows:
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61 {
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62 int fd;
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63 for (fd = 3; fd < 65536; fd++)
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64 if (dup2 (0, fd) == -1)
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65 break;
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66 return fd;
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67 }
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68 On Windows XP, the result is 2048.
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69 The drawback of this loop is that it allocates memory for a libc
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70 internal array that is never freed.
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71
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72 The number N can also be obtained as the upper bound for
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73 _getmaxstdio (). _getmaxstdio () returns the maximum number of open
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74 FILE objects. The sanity check in _setmaxstdio reveals the maximum
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75 number of file descriptors. This too allocates memory, but it is
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76 freed when we call _setmaxstdio with the original value. */
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77 int orig_max_stdio = _getmaxstdio ();
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78 unsigned int bound;
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79 for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
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80 ;
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81 _setmaxstdio (orig_max_stdio);
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82 dtablesize = bound;
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83 }
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84 return dtablesize;
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85 }
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86
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87 #elif HAVE_GETDTABLESIZE
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88
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89 # include <sys/resource.h>
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90 # undef getdtablesize
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91
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92 int
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93 rpl_getdtablesize(void)
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94 {
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95 /* To date, this replacement is only compiled for Cygwin 1.7.25,
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96 which auto-increased the RLIMIT_NOFILE soft limit until it
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97 hits the compile-time constant hard limit of 3200. Although
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98 that version of cygwin supported a child process inheriting
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99 a smaller soft limit, the smaller limit is not enforced, so
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100 we might as well just report the hard limit. */
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101 struct rlimit lim;
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102 if (!getrlimit (RLIMIT_NOFILE, &lim) && lim.rlim_max != RLIM_INFINITY)
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103 return lim.rlim_max;
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104 return getdtablesize ();
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105 }
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106
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107 #elif defined _SC_OPEN_MAX
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108
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109 int
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110 getdtablesize (void)
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111 {
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112 return sysconf (_SC_OPEN_MAX);
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113 }
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114
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115 #endif