lib/pipe2.c

   1 /* Create a pipe, with specific opening flags.
   2    Copyright (C) 2009-2025 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include <unistd.h>
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24
  25 #include "binary-io.h"
  26
  27 #if GNULIB_defined_O_NONBLOCK
  28 # include "nonblocking.h"
  29 #endif
  30
  31 #if defined _WIN32 && ! defined __CYGWIN__
  32 /* Native Windows API.  */
  33
  34 # include <io.h>
  35
  36 #endif
  37
  38 int
  39 pipe2 (int fd[2], int flags)
  40 {
  41   /* Mingw _pipe() corrupts fd on failure; also, if we succeed at
  42      creating the pipe but later fail at changing fcntl, we want
  43      to leave fd unchanged: https://austingroupbugs.net/view.php?id=467  */
  44   int tmp[2];
  45   tmp[0] = fd[0];
  46   tmp[1] = fd[1];
  47
  48 #if HAVE_PIPE2
  49 # undef pipe2
  50   /* Try the system call first, if it exists.  (We may be running with a glibc
  51      that has the function but with an older kernel that lacks it.)  */
  52   {
  53     /* Cache the information whether the system call really exists.  */
  54     static int have_pipe2_really; /* 0 = unknown, 1 = yes, -1 = no */
  55     if (have_pipe2_really >= 0)
  56       {
  57         int result = pipe2 (fd, flags);
  58         if (!(result < 0 && errno == ENOSYS))
  59           {
  60             have_pipe2_really = 1;
  61             return result;
  62           }
  63         have_pipe2_really = -1;
  64       }
  65   }
  66 #endif
  67
  68   /* Check the supported flags.  */
  69   if ((flags & ~(O_CLOEXEC | O_NONBLOCK | O_BINARY | O_TEXT)) != 0)
  70     {
  71       errno = EINVAL;
  72       return -1;
  73     }
  74
  75 #if defined _WIN32 && ! defined __CYGWIN__
  76 /* Native Windows API.  */
  77
  78   if (_pipe (fd, 4096, flags & ~O_NONBLOCK) < 0)
  79     {
  80       fd[0] = tmp[0];
  81       fd[1] = tmp[1];
  82       return -1;
  83     }
  84
  85   /* O_NONBLOCK handling.
  86      On native Windows platforms, O_NONBLOCK is defined by gnulib.  Use the
  87      functions defined by the gnulib module 'nonblocking'.  */
  88 # if GNULIB_defined_O_NONBLOCK
  89   if (flags & O_NONBLOCK)
  90     {
  91       if (set_nonblocking_flag (fd[0], true) != 0
  92           || set_nonblocking_flag (fd[1], true) != 0)
  93         goto fail;
  94     }
  95 # else
  96   {
  97     static_assert (O_NONBLOCK == 0);
  98   }
  99 # endif
 100
 101   return 0;
 102
 103 #else
 104 /* Unix API.  */
 105
 106   if (pipe (fd) < 0)
 107     return -1;
 108
 109   /* POSIX <https://pubs.opengroup.org/onlinepubs/9699919799/functions/pipe.html>
 110      says that initially, the O_NONBLOCK and FD_CLOEXEC flags are cleared on
 111      both fd[0] and fd[1].  */
 112
 113   /* O_NONBLOCK handling.
 114      On Unix platforms, O_NONBLOCK is defined by the system.  Use fcntl().  */
 115   if (flags & O_NONBLOCK)
 116     {
 117       int fcntl_flags;
 118
 119       if ((fcntl_flags = fcntl (fd[1], F_GETFL, 0)) < 0
 120           || fcntl (fd[1], F_SETFL, fcntl_flags | O_NONBLOCK) == -1
 121           || (fcntl_flags = fcntl (fd[0], F_GETFL, 0)) < 0
 122           || fcntl (fd[0], F_SETFL, fcntl_flags | O_NONBLOCK) == -1)
 123         goto fail;
 124     }
 125
 126   if (flags & O_CLOEXEC)
 127     {
 128       int fcntl_flags;
 129
 130       if ((fcntl_flags = fcntl (fd[1], F_GETFD, 0)) < 0
 131           || fcntl (fd[1], F_SETFD, fcntl_flags | FD_CLOEXEC) == -1
 132           || (fcntl_flags = fcntl (fd[0], F_GETFD, 0)) < 0
 133           || fcntl (fd[0], F_SETFD, fcntl_flags | FD_CLOEXEC) == -1)
 134         goto fail;
 135     }
 136
 137 # if O_BINARY
 138   if (flags & O_BINARY)
 139     {
 140       set_binary_mode (fd[1], O_BINARY);
 141       set_binary_mode (fd[0], O_BINARY);
 142     }
 143   else if (flags & O_TEXT)
 144     {
 145       set_binary_mode (fd[1], O_TEXT);
 146       set_binary_mode (fd[0], O_TEXT);
 147     }
 148 # endif
 149
 150   return 0;
 151
 152 #endif
 153
 154 #if GNULIB_defined_O_NONBLOCK || !(defined _WIN32 && ! defined __CYGWIN__)
 155  fail:
 156   {
 157     int saved_errno = errno;
 158     close (fd[0]);
 159     close (fd[1]);
 160     fd[0] = tmp[0];
 161     fd[1] = tmp[1];
 162     errno = saved_errno;
 163     return -1;
 164   }
 165 #endif
 166 }