spawn.c

/*
 * Copyright 2008-2013 Various Authors
 * Copyright 2005 Timo Hirvonen
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "spawn.h"
#include "file.h"

#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

int spawn(char *argv[], int *status, int do_wait)
{
	pid_t pid;
	int err_pipe[2];

	if (pipe(err_pipe) == -1)
		return -1;

	pid = fork();
	if (pid == -1) {
		/* error */
		return -1;
	} else if (pid == 0) {
		/* child */
		int dev_null, err, i;

		/* create grandchild and exit child to avoid zombie processes */
		if (!do_wait) {
			switch (fork()) {
			case 0:
				/* grandchild */
				break;
			case -1:
				/* error */
				_exit(127);
			default:
				/* parent of grandchild */
				_exit(0);
			}
		}

		close(err_pipe[0]);
		fcntl(err_pipe[1], F_SETFD, FD_CLOEXEC);

		/* redirect stdout and stderr to /dev/null if possible */
		dev_null = open("/dev/null", O_WRONLY);
		if (dev_null != -1) {
			dup2(dev_null, 1);
			dup2(dev_null, 2);
		}

		/* not interactive, close stdin */
		close(0);

		/* close unused fds */
		for (i = 3; i < 30; i++)
			close(i);

		execvp(argv[0], argv);

		/* error */
		err = errno;
		write_all(err_pipe[1], &err, sizeof(int));
		exit(1);
	} else {
		/* parent */
		int rc, errno_save, child_errno, tmp;

		close(err_pipe[1]);
		rc = read_all(err_pipe[0], &child_errno, sizeof(int));
		errno_save = errno;
		close(err_pipe[0]);

		if (!do_wait)
			status = &tmp;
		waitpid(pid, status, 0);

		if (rc == -1) {
			errno = errno_save;
			return -1;
		}
		if (rc == sizeof(int)) {
			errno = child_errno;
			return -1;
		}
		if (rc != 0) {
			errno = EMSGSIZE;
			return -1;
		}
		return 0;
	}
}