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annotate lib/popen.c @ 12421:e8d2c6fc33ad

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Use spaces for indentation, not tabs.
author Bruno Haible <bruno@clisp.org>
date Thu, 10 Dec 2009 20:28:30 +0100
parents f17a5ed578bd
children c2cbabec01dd
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 /* Open a stream to a sub-process.
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2 Copyright (C) 2009 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 3 of the License, or
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7 (at your option) 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, see <http://www.gnu.org/licenses/>. */
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16
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17 /* Written by Eric Blake <ebb9@byu.net>, 2009. */
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18
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19 #include <config.h>
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20
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21 /* Specification. */
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22 #include <stdio.h>
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23
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24 #include <errno.h>
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25 #include <fcntl.h>
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26 #include <stdlib.h>
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27 #include <unistd.h>
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28
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29 #undef popen
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30
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31 FILE *
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32 rpl_popen (const char *filename, const char *mode)
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33 {
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34 /* The mingw popen works fine, and all other platforms have fcntl.
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35 The bug of the child clobbering its own file descriptors if stdin
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36 or stdout was closed in the parent can be worked around by
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37 opening those two fds as close-on-exec to begin with. */
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38 /* Cygwin 1.5.x also has a bug where the popen fd is improperly
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39 marked close-on-exec, and if the application undoes this, then
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40 the fd leaks into subsequent popen calls. We could work around
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41 this by maintaining a list of all fd's opened by popen, and
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42 temporarily marking them cloexec around the real popen call, but
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43 we would also have to override pclose, and the bookkeepping seems
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44 extreme given that cygwin 1.7 no longer has the bug. */
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45 FILE *result;
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46 int cloexec0 = fcntl (STDIN_FILENO, F_GETFD);
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47 int cloexec1 = fcntl (STDOUT_FILENO, F_GETFD);
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48 int saved_errno;
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49
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50 /* If either stdin or stdout was closed (that is, fcntl failed),
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51 then we open a dummy close-on-exec fd to occupy that slot. That
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52 way, popen's internal use of pipe() will not contain either fd 0
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53 or 1, overcoming the fact that the child process blindly calls
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54 close() on the parent's end of the pipe without first checking
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55 whether it is clobbering the fd just placed there via dup2(); the
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56 exec will get rid of the dummy fd's in the child. Fortunately,
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57 closed stderr in the parent does not cause problems in the
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58 child. */
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59 if (cloexec0 < 0)
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60 {
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61 if (open ("/dev/null", O_RDONLY) != STDIN_FILENO
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62 || fcntl (STDIN_FILENO, F_SETFD,
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63 fcntl (STDIN_FILENO, F_GETFD) | FD_CLOEXEC) == -1)
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64 abort ();
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65 }
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66 if (cloexec1 < 0)
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67 {
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68 if (open ("/dev/null", O_RDONLY) != STDOUT_FILENO
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69 || fcntl (STDOUT_FILENO, F_SETFD,
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70 fcntl (STDOUT_FILENO, F_GETFD) | FD_CLOEXEC) == -1)
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71 abort ();
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72 }
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73 result = popen (filename, mode);
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74 /* Now, close any dummy fd's created in the parent. */
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75 saved_errno = errno;
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76 if (cloexec0 < 0)
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77 close (STDIN_FILENO);
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78 if (cloexec1 < 0)
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79 close (STDOUT_FILENO);
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80 errno = saved_errno;
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81 return result;
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82 }