1 /* Creation of subprocesses, communicating via pipes. 2 Copyright (C) 2001-2003, 2006, 2008-2012 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 <http://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 If slave_process is true, the child process will be terminated when its 46 creator receives a catchable fatal signal or exits normally. If 47 slave_process is false, the child process will continue running in this 48 case, until it is lucky enough to attempt to communicate with its creator 49 and thus get a SIGPIPE signal. 50 51 If exit_on_error is false, a child process id of -1 should be treated the 52 same way as a subprocess which accepts no input, produces no output and 53 terminates with exit code 127. Why? Some errors during posix_spawnp() 54 cause the function posix_spawnp() to return an error code; some other 55 errors cause the subprocess to exit with return code 127. It is 56 implementation dependent which error is reported which way. The caller 57 must treat both cases as equivalent. 58 59 It is recommended that no signal is blocked or ignored (i.e. have a 60 signal handler with value SIG_IGN) while any of these functions is called. 61 The reason is that child processes inherit the mask of blocked signals 62 from their parent (both through posix_spawn() and fork()/exec()); 63 likewise, signals ignored in the parent are also ignored in the child 64 (except possibly for SIGCHLD). And POSIX:2001 says [in the description 65 of exec()]: 66 "it should be noted that many existing applications wrongly 67 assume that they start with certain signals set to the default 68 action and/or unblocked. In particular, applications written 69 with a simpler signal model that does not include blocking of 70 signals, such as the one in the ISO C standard, may not behave 71 properly if invoked with some signals blocked. Therefore, it is 72 best not to block or ignore signals across execs without explicit 73 reason to do so, and especially not to block signals across execs 74 of arbitrary (not closely co-operating) programs." */ 75 76 /* Open a pipe for output to a child process. 77 * The child's stdout goes to a file. 78 * 79 * write system read 80 * parent -> fd[0] -> STDIN_FILENO -> child 81 * 82 * Note: When writing to a child process, it is useful to ignore the SIGPIPE 83 * signal and the EPIPE error code. 84 */ 85 extern pid_t create_pipe_out (const char *progname, 86 const char *prog_path, char **prog_argv, 87 const char *prog_stdout, bool null_stderr, 88 bool slave_process, bool exit_on_error, 89 int fd[1]); 90 91 /* Open a pipe for input from a child process. 92 * The child's stdin comes from a file. 93 * 94 * read system write 95 * parent <- fd[0] <- STDOUT_FILENO <- child 96 * 97 */ 98 extern pid_t create_pipe_in (const char *progname, 99 const char *prog_path, char **prog_argv, 100 const char *prog_stdin, bool null_stderr, 101 bool slave_process, bool exit_on_error, 102 int fd[1]); 103 104 /* Open a bidirectional pipe. 105 * 106 * write system read 107 * parent -> fd[1] -> STDIN_FILENO -> child 108 * parent <- fd[0] <- STDOUT_FILENO <- child 109 * read system write 110 * 111 * Note: When writing to a child process, it is useful to ignore the SIGPIPE 112 * signal and the EPIPE error code. 113 * 114 * Note: The parent process must be careful to avoid deadlock. 115 * 1) If you write more than PIPE_MAX bytes or, more generally, if you write 116 * more bytes than the subprocess can handle at once, the subprocess 117 * may write its data and wait on you to read it, but you are currently 118 * busy writing. 119 * 2) When you don't know ahead of time how many bytes the subprocess 120 * will produce, the usual technique of calling read (fd, buf, BUFSIZ) 121 * with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause 122 * the read() call to block until *all* of the buffer has been filled. 123 * But the subprocess cannot produce more data until you gave it more 124 * input. But you are currently busy reading from it. 125 */ 126 extern pid_t create_pipe_bidi (const char *progname, 127 const char *prog_path, char **prog_argv, 128 bool null_stderr, 129 bool slave_process, bool exit_on_error, 130 int fd[2]); 131 132 /* The name of the "always silent" device. */ 133 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__ 134 /* Native Windows API. */ 135 # define DEV_NULL "NUL" 136 #else 137 /* Unix API. */ 138 # define DEV_NULL "/dev/null" 139 #endif 140 141 142 #ifdef __cplusplus 143 } 144 #endif 145 146 147 #endif /* _SPAWN_PIPE_H */ 148