1 /* Creation of subprocesses, communicating via pipes.
2 Copyright (C) 2001-2003, 2006, 2008-2009 Free Software Foundation, Inc.
3 Written by Bruno Haible <haible@clisp.cons.org>, 2001.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
24 #include <sys/types.h>
34 /* All these functions create a subprocess and don't wait for its termination.
35 They return the process id of the subprocess. They also return in fd[]
36 one or two file descriptors for communication with the subprocess.
37 If the subprocess creation fails: if exit_on_error is true, the main
38 process exits with an error message; otherwise, an error message is given
39 if null_stderr is false, then -1 is returned and fd[] remain uninitialized.
41 After finishing communication, the caller should call wait_subprocess()
42 to get rid of the subprocess in the process table.
44 If slave_process is true, the child process will be terminated when its
45 creator receives a catchable fatal signal or exits normally. If
46 slave_process is false, the child process will continue running in this
47 case, until it is lucky enough to attempt to communicate with its creator
48 and thus get a SIGPIPE signal.
50 If exit_on_error is false, a child process id of -1 should be treated the
51 same way as a subprocess which accepts no input, produces no output and
52 terminates with exit code 127. Why? Some errors during posix_spawnp()
53 cause the function posix_spawnp() to return an error code; some other
54 errors cause the subprocess to exit with return code 127. It is
55 implementation dependent which error is reported which way. The caller
56 must treat both cases as equivalent.
58 It is recommended that no signal is blocked or ignored (i.e. have a
59 signal handler with value SIG_IGN) while any of these functions is called.
60 The reason is that child processes inherit the mask of blocked signals
61 from their parent (both through posix_spawn() and fork()/exec());
62 likewise, signals ignored in the parent are also ignored in the child
63 (except possibly for SIGCHLD). And POSIX:2001 says [in the description
65 "it should be noted that many existing applications wrongly
66 assume that they start with certain signals set to the default
67 action and/or unblocked. In particular, applications written
68 with a simpler signal model that does not include blocking of
69 signals, such as the one in the ISO C standard, may not behave
70 properly if invoked with some signals blocked. Therefore, it is
71 best not to block or ignore signals across execs without explicit
72 reason to do so, and especially not to block signals across execs
73 of arbitrary (not closely co-operating) programs." */
75 /* Open a pipe for output to a child process.
76 * The child's stdout goes to a file.
79 * parent -> fd[0] -> STDIN_FILENO -> child
81 * Note: When writing to a child process, it is useful to ignore the SIGPIPE
82 * signal and the EPIPE error code.
84 extern pid_t create_pipe_out (const char *progname,
85 const char *prog_path, char **prog_argv,
86 const char *prog_stdout, bool null_stderr,
87 bool slave_process, bool exit_on_error,
90 /* Open a pipe for input from a child process.
91 * The child's stdin comes from a file.
94 * parent <- fd[0] <- STDOUT_FILENO <- child
97 extern pid_t create_pipe_in (const char *progname,
98 const char *prog_path, char **prog_argv,
99 const char *prog_stdin, bool null_stderr,
100 bool slave_process, bool exit_on_error,
103 /* Open a bidirectional pipe.
106 * parent -> fd[1] -> STDIN_FILENO -> child
107 * parent <- fd[0] <- STDOUT_FILENO <- child
110 * Note: When writing to a child process, it is useful to ignore the SIGPIPE
111 * signal and the EPIPE error code.
113 * Note: The parent process must be careful to avoid deadlock.
114 * 1) If you write more than PIPE_MAX bytes or, more generally, if you write
115 * more bytes than the subprocess can handle at once, the subprocess
116 * may write its data and wait on you to read it, but you are currently
118 * 2) When you don't know ahead of time how many bytes the subprocess
119 * will produce, the usual technique of calling read (fd, buf, BUFSIZ)
120 * with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause
121 * the read() call to block until *all* of the buffer has been filled.
122 * But the subprocess cannot produce more data until you gave it more
123 * input. But you are currently busy reading from it.
125 extern pid_t create_pipe_bidi (const char *progname,
126 const char *prog_path, char **prog_argv,
128 bool slave_process, bool exit_on_error,
131 /* The name of the "always silent" device. */
132 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
133 /* Native Woe32 API. */
134 # define DEV_NULL "NUL"
137 # define DEV_NULL "/dev/null"