obs-studio/plugins/linux-v4l2/v4l2-udev.c

/*
Copyright (C) 2014 by Leonhard Oelke <leonhard@in-verted.de>

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 <sys/eventfd.h>
#include <poll.h>
#include <unistd.h>
#include <libudev.h>

#include <util/threading.h>
#include <util/darray.h>
#include <obs.h>

#include "v4l2-udev.h"

/** udev action enum */
enum udev_action {
	UDEV_ACTION_ADDED,
	UDEV_ACTION_REMOVED,
	UDEV_ACTION_UNKNOWN
};

static const char *udev_signals[] = {"void device_added(string device)",
				     "void device_removed(string device)",
				     NULL};

/* global data */
static uint_fast32_t udev_refs = 0;
static pthread_mutex_t udev_mutex = PTHREAD_MUTEX_INITIALIZER;

static pthread_t udev_thread;
static os_event_t *udev_event;
static int udev_event_fd;

static signal_handler_t *udev_signalhandler = NULL;

/**
 * udev gives us the device action as string, so we convert it here ...
 *
 * @param action the udev action as string
 * @return the udev action as enum value
 */
static enum udev_action udev_action_to_enum(const char *action)
{
	if (!action)
		return UDEV_ACTION_UNKNOWN;

	if (!strncmp("add", action, 3))
		return UDEV_ACTION_ADDED;
	if (!strncmp("remove", action, 6))
		return UDEV_ACTION_REMOVED;

	return UDEV_ACTION_UNKNOWN;
}

/**
 * Call all registered callbacks with the event
 *
 * @param dev udev device that had an event occuring
 */
static inline void udev_signal_event(struct udev_device *dev)
{
	const char *node;
	enum udev_action action;
	struct calldata data;

	pthread_mutex_lock(&udev_mutex);

	node = udev_device_get_devnode(dev);
	action = udev_action_to_enum(udev_device_get_action(dev));

	calldata_init(&data);

	calldata_set_string(&data, "device", node);

	switch (action) {
	case UDEV_ACTION_ADDED:
		signal_handler_signal(udev_signalhandler, "device_added",
				      &data);
		break;
	case UDEV_ACTION_REMOVED:
		signal_handler_signal(udev_signalhandler, "device_removed",
				      &data);
		break;
	default:
		break;
	}

	calldata_free(&data);

	pthread_mutex_unlock(&udev_mutex);
}

/**
 * Event listener thread
 */
static void *udev_event_thread(void *vptr)
{
	UNUSED_PARAMETER(vptr);

	int fd;
	struct udev *udev;
	struct udev_monitor *mon;
	struct udev_device *dev;

	/* set up udev monitoring */
	os_set_thread_name("v4l2: udev");
	udev = udev_new();
	mon = udev_monitor_new_from_netlink(udev, "udev");
	udev_monitor_filter_add_match_subsystem_devtype(mon, "video4linux",
							NULL);
	if (udev_monitor_enable_receiving(mon) < 0)
		return NULL;

	/* set up fds */
	fd = udev_monitor_get_fd(mon);

	while (os_event_try(udev_event) == EAGAIN) {
		struct pollfd fds[2];

		fds[0].fd = fd;
		fds[0].events = POLLIN;
		fds[0].revents = 0;
		fds[1].fd = udev_event_fd;
		fds[1].events = POLLIN;

		if (poll(fds, 2, 1000) <= 0)
			continue;

		if (!(fds[0].revents & POLLIN))
			continue;

		dev = udev_monitor_receive_device(mon);
		if (!dev)
			continue;

		udev_signal_event(dev);

		udev_device_unref(dev);
	}

	udev_monitor_unref(mon);
	udev_unref(udev);

	return NULL;
}

void v4l2_init_udev(void)
{
	pthread_mutex_lock(&udev_mutex);

	/* set up udev */
	if (udev_refs == 0) {
		if (os_event_init(&udev_event, OS_EVENT_TYPE_MANUAL) != 0)
			goto fail;
		if ((udev_event_fd = eventfd(0, EFD_CLOEXEC)) < 0)
			goto fail;
		if (pthread_create(&udev_thread, NULL, udev_event_thread,
				   NULL) != 0) {
			close(udev_event_fd);
			goto fail;
		}

		udev_signalhandler = signal_handler_create();
		if (!udev_signalhandler) {
			close(udev_event_fd);
			goto fail;
		}
		signal_handler_add_array(udev_signalhandler, udev_signals);
	}
	udev_refs++;

fail:
	pthread_mutex_unlock(&udev_mutex);
}

void v4l2_unref_udev(void)
{
	pthread_mutex_lock(&udev_mutex);

	/* unref udev monitor */
	if (udev_refs && --udev_refs == 0) {
		os_event_signal(udev_event);
		eventfd_write(udev_event_fd, 1);
		pthread_join(udev_thread, NULL);
		os_event_destroy(udev_event);
		close(udev_event_fd);

		if (udev_signalhandler)
			signal_handler_destroy(udev_signalhandler);
		udev_signalhandler = NULL;
	}

	pthread_mutex_unlock(&udev_mutex);
}

signal_handler_t *v4l2_get_udev_signalhandler(void)
{
	return udev_signalhandler;
}