1 /* Creation of subprocesses, communicating via pipes.
2 Copyright (C) 2001-2003, 2006, 2008-2021 Free Software Foundation, Inc.
3 Written by Bruno Haible <haible@clisp.cons.org>, 2001.
4
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.
9
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.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 #ifndef _SPAWN_PIPE_H
19 #define _SPAWN_PIPE_H
20
21 /* Get pid_t. */
22 #include <stdlib.h>
23 #include <unistd.h>
24 #include <sys/types.h>
25
26 #include <stdbool.h>
27
28
29 #ifdef __cplusplus
30 extern "C" {
31 #endif
32
33
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, with errno set, and fd[]
40 remain uninitialized.
41
42 After finishing communication, the caller should call wait_subprocess()
43 to get rid of the subprocess in the process table.
44
45 progname is the name of the program to be executed by the subprocess, used
46 for error messages.
47 prog_path is the file name of the program to be executed by the subprocess.
48 If it contains no slashes, a search is conducted in $PATH. An operating
49 system dependent suffix is added, if necessary.
50 prog_argv is the array of strings that the subprocess shall receive in
51 argv[]. It is a NULL-terminated array. prog_argv[0] should normally be
52 identical to prog_path.
53
54 If directory is not NULL, the subprocess is started in that directory. If
55 prog_path is a relative file name, it resolved before changing to that
56 directory. The current directory of the current process remains unchanged.
57
58 If slave_process is true, the child process will be terminated when its
59 creator receives a catchable fatal signal or exits normally. If
60 slave_process is false, the child process will continue running in this
61 case, until it is lucky enough to attempt to communicate with its creator
62 and thus get a SIGPIPE signal.
63
64 If exit_on_error is false, a child process id of -1 should be treated the
65 same way as a subprocess which accepts no input, produces no output and
66 terminates with exit code 127. Why? Some errors during posix_spawnp()
67 cause the function posix_spawnp() to return an error code; some other
68 errors cause the subprocess to exit with return code 127. It is
69 implementation dependent which error is reported which way. The caller
70 must treat both cases as equivalent.
71
72 It is recommended that no signal is blocked or ignored (i.e. have a
73 signal handler with value SIG_IGN) while any of these functions is called.
74 The reason is that child processes inherit the mask of blocked signals
75 from their parent (both through posix_spawn() and fork()/exec());
76 likewise, signals ignored in the parent are also ignored in the child
77 (except possibly for SIGCHLD). And POSIX:2001 says [in the description
78 of exec()]:
79 "it should be noted that many existing applications wrongly
80 assume that they start with certain signals set to the default
81 action and/or unblocked. In particular, applications written
82 with a simpler signal model that does not include blocking of
83 signals, such as the one in the ISO C standard, may not behave
84 properly if invoked with some signals blocked. Therefore, it is
85 best not to block or ignore signals across execs without explicit
86 reason to do so, and especially not to block signals across execs
87 of arbitrary (not closely co-operating) programs." */
88
89 /* Open a pipe for output to a child process.
90 * The child's stdout goes to a file.
91 *
92 * write system read
93 * parent -> fd[0] -> STDIN_FILENO -> child
94 *
95 * Note: When writing to a child process, it is useful to ignore the SIGPIPE
96 * signal and the EPIPE error code.
97 */
98 extern pid_t create_pipe_out (const char *progname,
99 const char *prog_path,
100 const char * const *prog_argv,
101 const char *directory,
102 const char *prog_stdout, bool null_stderr,
103 bool slave_process, bool exit_on_error,
104 int fd[1]);
105
106 /* Open a pipe for input from a child process.
107 * The child's stdin comes from a file.
108 *
109 * read system write
110 * parent <- fd[0] <- STDOUT_FILENO <- child
111 *
112 */
113 extern pid_t create_pipe_in (const char *progname,
114 const char *prog_path,
115 const char * const *prog_argv,
116 const char *directory,
117 const char *prog_stdin, bool null_stderr,
118 bool slave_process, bool exit_on_error,
119 int fd[1]);
120
121 /* Open a bidirectional pipe.
122 *
123 * write system read
124 * parent -> fd[1] -> STDIN_FILENO -> child
125 * parent <- fd[0] <- STDOUT_FILENO <- child
126 * read system write
127 *
128 * Note: When writing to a child process, it is useful to ignore the SIGPIPE
129 * signal and the EPIPE error code.
130 *
131 * Note: The parent process must be careful to avoid deadlock.
132 * 1) If you write more than PIPE_MAX bytes or, more generally, if you write
133 * more bytes than the subprocess can handle at once, the subprocess
134 * may write its data and wait on you to read it, but you are currently
135 * busy writing.
136 * 2) When you don't know ahead of time how many bytes the subprocess
137 * will produce, the usual technique of calling read (fd, buf, BUFSIZ)
138 * with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause
139 * the read() call to block until *all* of the buffer has been filled.
140 * But the subprocess cannot produce more data until you gave it more
141 * input. But you are currently busy reading from it.
142 */
143 extern pid_t create_pipe_bidi (const char *progname,
144 const char *prog_path,
145 const char * const *prog_argv,
146 const char *directory,
147 bool null_stderr,
148 bool slave_process, bool exit_on_error,
149 int fd[2]);
150
151 /* The name of the "always silent" device. */
152 #if defined _WIN32 && ! defined __CYGWIN__
153 /* Native Windows API. */
154 # define DEV_NULL "NUL"
155 #else
156 /* Unix API. */
157 # define DEV_NULL "/dev/null"
158 #endif
159
160
161 #ifdef __cplusplus
162 }
163 #endif
164
165
166 #endif /* _SPAWN_PIPE_H */