PX4-Autopilot/src/modules/mavlink/mavlink_shell.cpp

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/**
 * @file mavlink_shell.cpp
 * A shell to be used via MAVLink
 *
 * @author Beat Küng <beat-kueng@gmx.net>
 */

#include "mavlink_shell.h"
#include <px4_platform_common/defines.h>

#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>


#ifdef __PX4_NUTTX
#include <nshlib/nshlib.h>
#endif /* __PX4_NUTTX */

#ifdef __PX4_CYGWIN
#include <asm/socket.h>
#endif

MavlinkShell::~MavlinkShell()
{
	//closing the pipes will stop the thread as well
	if (_to_shell_fd >= 0) {
		PX4_INFO("Stopping mavlink shell");
		close(_to_shell_fd);
	}

	if (_from_shell_fd >= 0) {
		close(_from_shell_fd);
	}
}

int MavlinkShell::start()
{
	//this currently only works for NuttX
#ifndef __PX4_NUTTX
	return -1;
#endif /* __PX4_NUTTX */


	PX4_INFO("Starting mavlink shell");

	int p1[2], p2[2];

	/* Create the shell task and redirect its stdin & stdout. If we used pthread, we would redirect
	 * stdin/out of the calling process as well, so we need px4_task_spawn_cmd. However NuttX only
	 * keeps (duplicates) the first 3 fd's when creating a new task, all others are not inherited.
	 * This means we need to temporarily change the first 3 fd's of the current task (or at least
	 * the first 2 if stdout=stderr).
	 */

	if (pipe(p1) != 0) {
		return -errno;
	}

	if (pipe(p2) != 0) {
		close(p1[0]);
		close(p1[1]);
		return -errno;
	}

	int ret = 0;

	_from_shell_fd  = p1[0];
	_to_shell_fd = p2[1];
	_shell_fds[0]  = p2[0];
	_shell_fds[1] = p1[1];

	/*
	 * Ensure that during the temporary phase no other thread from the same task writes to
	 * stdout (as it would end up in the pipe).
	 */
#ifdef __PX4_NUTTX
	sched_lock();
#endif /* __PX4_NUTTX */
	fflush(stdout);
	fflush(stderr);

	int fd_backups[2]; //we don't touch stderr, we will redirect it to stdout in the startup of the shell task

	for (int i = 0; i < 2; ++i) {
		fd_backups[i] = dup(i);

		if (fd_backups[i] == -1) {
			ret = -errno;
		}
	}

	dup2(_shell_fds[0], 0);
	dup2(_shell_fds[1], 1);

	if (ret == 0) {
		_task = px4_task_spawn_cmd("mavlink_shell",
					   SCHED_DEFAULT,
					   SCHED_PRIORITY_DEFAULT,
					   2048,
					   &MavlinkShell::shell_start_thread,
					   nullptr);

		if (_task < 0) {
			ret = -1;
		}
	}

	//restore fd's
	for (int i = 0; i < 2; ++i) {
		if (dup2(fd_backups[i], i) == -1) {
			ret = -errno;
		}

		close(fd_backups[i]);
	}

	//close unused pipe fd's
	close(_shell_fds[0]);
	close(_shell_fds[1]);

#ifdef __PX4_NUTTX
	sched_unlock();
#endif /* __PX4_NUTTX */

	return ret;
}

int MavlinkShell::shell_start_thread(int argc, char *argv[])
{
	dup2(1, 2); //redirect stderror to stdout

#ifdef __PX4_NUTTX
	nsh_consolemain(0, NULL);
#endif /* __PX4_NUTTX */

	return 0;
}

size_t MavlinkShell::write(uint8_t *buffer, size_t len)
{
	return ::write(_to_shell_fd, buffer, len);
}

size_t MavlinkShell::read(uint8_t *buffer, size_t len)
{
	return ::read(_from_shell_fd, buffer, len);
}

size_t MavlinkShell::available()
{
	int ret = 0;

	if (ioctl(_from_shell_fd, FIONREAD, (unsigned long)&ret) == OK) {
		return ret;
	}

	return 0;
}