v4l2loopback.c

/* -*- c-file-style: "linux" -*- */
/*
 * v4l2loopback.c  --  video4linux2 loopback driver
 *
 * Copyright (C) 2005-2009 Vasily Levin (vasaka@gmail.com)
 * Copyright (C) 2010-2023 IOhannes m zmoelnig (zmoelnig@iem.at)
 * Copyright (C) 2011 Stefan Diewald (stefan.diewald@mytum.de)
 * Copyright (C) 2012 Anton Novikov (random.plant@gmail.com)
 *
 * 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.
 *
 */
#include <linux/version.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/module.h>
#include <linux/videodev2.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/capability.h>
#include <linux/timer.h>
#include <linux/eventpoll.h>
#include <media/v4l2-ioctl.h>
#include <media/v4l2-common.h>
#include <media/v4l2-device.h>
#include <media/v4l2-ctrls.h>
#include <media/v4l2-event.h>

#include <linux/miscdevice.h>
#include "v4l2loopback.h"

#define V4L2LOOPBACK_CTL_ADD_legacy 0x4C80
#define V4L2LOOPBACK_CTL_REMOVE_legacy 0x4C81
#define V4L2LOOPBACK_CTL_QUERY_legacy 0x4C82

#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 0, 0)
#error This module is not supported on kernels before 4.0.0.
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 3, 0)
#define strscpy strlcpy
#endif

#if defined(timer_setup)
#define HAVE_TIMER_SETUP
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 7, 0)
#define VFL_TYPE_VIDEO VFL_TYPE_GRABBER
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 2, 0)
#define timer_delete_sync del_timer_sync
#endif

#define fh_to_opener(ptr) container_of((ptr), struct v4l2_loopback_opener, fh)
#define file_to_opener(ptr) \
	container_of(file_to_v4l2_fh(ptr), struct v4l2_loopback_opener, fh)

#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 18, 0)
#define v4l2l_f_to_opener(_file, _fh) fh_to_opener(_fh)
#define v4l2_fh_add(fh, filp) v4l2_fh_add(fh)
#define v4l2_fh_del(fh, filp) v4l2_fh_del(fh)
#else
#define v4l2l_f_to_opener(_file, _fh) file_to_opener(_file)
#endif

#define V4L2LOOPBACK_VERSION_CODE                                              \
	KERNEL_VERSION(V4L2LOOPBACK_VERSION_MAJOR, V4L2LOOPBACK_VERSION_MINOR, \
		       V4L2LOOPBACK_VERSION_BUGFIX)

MODULE_DESCRIPTION("V4L2 loopback video device");
MODULE_AUTHOR("Vasily Levin, "
	      "IOhannes m zmoelnig <zmoelnig@iem.at>,"
	      "Stefan Diewald,"
	      "Anton Novikov"
	      "et al.");
#ifdef SNAPSHOT_VERSION
MODULE_VERSION(__stringify(SNAPSHOT_VERSION));
#else
MODULE_VERSION("" __stringify(V4L2LOOPBACK_VERSION_MAJOR) "." __stringify(
	V4L2LOOPBACK_VERSION_MINOR) "." __stringify(V4L2LOOPBACK_VERSION_BUGFIX));
#endif
MODULE_LICENSE("GPL");

/*
 * helpers
 */
#define dprintk(fmt, args...)                                          \
	do {                                                           \
		if (debug > 0) {                                       \
			printk(KERN_INFO "v4l2-loopback[" __stringify( \
				       __LINE__) "], pid(%d):  " fmt,  \
			       task_pid_nr(current), ##args);          \
		}                                                      \
	} while (0)

#define MARK()                                                             \
	do {                                                               \
		if (debug > 1) {                                           \
			printk(KERN_INFO "%s:%d[%s], pid(%d)\n", __FILE__, \
			       __LINE__, __func__, task_pid_nr(current));  \
		}                                                          \
	} while (0)

#define dprintkrw(fmt, args...)                                        \
	do {                                                           \
		if (debug > 2) {                                       \
			printk(KERN_INFO "v4l2-loopback[" __stringify( \
				       __LINE__) "], pid(%d): " fmt,   \
			       task_pid_nr(current), ##args);          \
		}                                                      \
	} while (0)

static inline void v4l2l_get_timestamp(struct v4l2_buffer *b)
{
	struct timespec64 ts;
	ktime_get_ts64(&ts);

	b->timestamp.tv_sec = ts.tv_sec;
	b->timestamp.tv_usec = (ts.tv_nsec / NSEC_PER_USEC);
	b->flags |= V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
	b->flags &= ~V4L2_BUF_FLAG_TIMESTAMP_COPY;
}

#if BITS_PER_LONG == 32
#include <asm/div64.h> /* do_div() for 64bit division */
static inline int v4l2l_mod64(const s64 A, const u32 B)
{
	u64 a = (u64)A;
	u32 b = B;

	if (A > 0)
		return do_div(a, b);
	a = -A;
	return -do_div(a, b);
}
#else
static inline int v4l2l_mod64(const s64 A, const u32 B)
{
	return A % B;
}
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 16, 0)
typedef unsigned __poll_t;
#endif

/* module constants
 *  can be overridden during he build process using something like
 *	make KCPPFLAGS="-DMAX_DEVICES=100"
 */

/* maximum number of v4l2loopback devices that can be created */
#ifndef MAX_DEVICES
#define MAX_DEVICES 16
#endif

/* whether the default is to announce capabilities exclusively or not */
#ifndef V4L2LOOPBACK_DEFAULT_EXCLUSIVECAPS
#define V4L2LOOPBACK_DEFAULT_EXCLUSIVECAPS 0
#endif

/* when a producer is considered to have gone stale */
#ifndef MAX_TIMEOUT
#define MAX_TIMEOUT (100 * 1000) /* in msecs */
#endif

/* max buffers that can be mapped, actually they
 * are all mapped to max_buffers buffers */
#ifndef MAX_BUFFERS
#define MAX_BUFFERS 32
#endif

/* module parameters */
static int debug = 0;
module_param(debug, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug, "debugging level (higher values == more verbose)");

#define V4L2LOOPBACK_DEFAULT_MAX_BUFFERS 2
static int max_buffers = V4L2LOOPBACK_DEFAULT_MAX_BUFFERS;
module_param(max_buffers, int, S_IRUGO);
MODULE_PARM_DESC(max_buffers,
		 "how many buffers should be allocated [DEFAULT: " __stringify(
			 V4L2LOOPBACK_DEFAULT_MAX_BUFFERS) "]");

/* how many times a device can be opened
 * the per-module default value can be overridden on a per-device basis using
 * the /sys/devices interface
 *
 * note that max_openers should be at least 2 in order to get a working system:
 *   one opener for the producer and one opener for the consumer
 *   however, we leave that to the user
 */
#define V4L2LOOPBACK_DEFAULT_MAX_OPENERS 10
static int max_openers = V4L2LOOPBACK_DEFAULT_MAX_OPENERS;
module_param(max_openers, int, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(
	max_openers,
	"how many users can open the loopback device [DEFAULT: " __stringify(
		V4L2LOOPBACK_DEFAULT_MAX_OPENERS) "]");

static int devices = -1;
module_param(devices, int, 0);
MODULE_PARM_DESC(devices, "how many devices should be created");

static int video_nr[MAX_DEVICES] = { [0 ...(MAX_DEVICES - 1)] = -1 };
module_param_array(video_nr, int, NULL, 0444);
MODULE_PARM_DESC(video_nr,
		 "video device numbers (-1=auto, 0=/dev/video0, etc.)");

static char *card_label[MAX_DEVICES];
module_param_array(card_label, charp, NULL, 0000);
MODULE_PARM_DESC(card_label, "card labels for each device");

static bool exclusive_caps[MAX_DEVICES] = {
	[0 ...(MAX_DEVICES - 1)] = V4L2LOOPBACK_DEFAULT_EXCLUSIVECAPS
};
module_param_array(exclusive_caps, bool, NULL, 0444);
/* FIXXME: wording */
MODULE_PARM_DESC(
	exclusive_caps,
	"whether to announce OUTPUT/CAPTURE capabilities exclusively or not  [DEFAULT: " __stringify(
		V4L2LOOPBACK_DEFAULT_EXCLUSIVECAPS) "]");

/* format specifications */
#define V4L2LOOPBACK_SIZE_MIN_WIDTH 2
#define V4L2LOOPBACK_SIZE_MIN_HEIGHT 1
#define V4L2LOOPBACK_SIZE_DEFAULT_MAX_WIDTH 8192
#define V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT 8192

#define V4L2LOOPBACK_SIZE_DEFAULT_WIDTH 640
#define V4L2LOOPBACK_SIZE_DEFAULT_HEIGHT 480

static int max_width = V4L2LOOPBACK_SIZE_DEFAULT_MAX_WIDTH;
module_param(max_width, int, S_IRUGO);
MODULE_PARM_DESC(max_width,
		 "maximum allowed frame width [DEFAULT: " __stringify(
			 V4L2LOOPBACK_SIZE_DEFAULT_MAX_WIDTH) "]");
static int max_height = V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT;
module_param(max_height, int, S_IRUGO);
MODULE_PARM_DESC(max_height,
		 "maximum allowed frame height [DEFAULT: " __stringify(
			 V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT) "]");

static DEFINE_IDR(v4l2loopback_index_idr);
static DEFINE_MUTEX(v4l2loopback_ctl_mutex);

/* frame intervals */
#define V4L2LOOPBACK_FRAME_INTERVAL_MAX __UINT32_MAX__
#define V4L2LOOPBACK_FPS_DEFAULT 30
#define V4L2LOOPBACK_FPS_MAX 1000

/* control IDs */
#define V4L2LOOPBACK_CID_BASE (V4L2_CID_USER_BASE | 0xf000)
#define CID_KEEP_FORMAT (V4L2LOOPBACK_CID_BASE + 0)
#define CID_SUSTAIN_FRAMERATE (V4L2LOOPBACK_CID_BASE + 1)
#define CID_TIMEOUT (V4L2LOOPBACK_CID_BASE + 2)
#define CID_TIMEOUT_IMAGE_IO (V4L2LOOPBACK_CID_BASE + 3)

static int v4l2loopback_s_ctrl(struct v4l2_ctrl *ctrl);
static const struct v4l2_ctrl_ops v4l2loopback_ctrl_ops = {
	.s_ctrl = v4l2loopback_s_ctrl,
};
static const struct v4l2_ctrl_config v4l2loopback_ctrl_keepformat = {
	// clang-format off
	.ops	= &v4l2loopback_ctrl_ops,
	.id	= CID_KEEP_FORMAT,
	.name	= "keep_format",
	.type	= V4L2_CTRL_TYPE_BOOLEAN,
	.min	= 0,
	.max	= 1,
	.step	= 1,
	.def	= 0,
	// clang-format on
};
static const struct v4l2_ctrl_config v4l2loopback_ctrl_sustainframerate = {
	// clang-format off
	.ops	= &v4l2loopback_ctrl_ops,
	.id	= CID_SUSTAIN_FRAMERATE,
	.name	= "sustain_framerate",
	.type	= V4L2_CTRL_TYPE_BOOLEAN,
	.min	= 0,
	.max	= 1,
	.step	= 1,
	.def	= 0,
	// clang-format on
};
static const struct v4l2_ctrl_config v4l2loopback_ctrl_timeout = {
	// clang-format off
	.ops	= &v4l2loopback_ctrl_ops,
	.id	= CID_TIMEOUT,
	.name	= "timeout",
	.type	= V4L2_CTRL_TYPE_INTEGER,
	.min	= 0,
	.max	= MAX_TIMEOUT,
	.step	= 1,
	.def	= 0,
	// clang-format on
};
static const struct v4l2_ctrl_config v4l2loopback_ctrl_timeoutimageio = {
	// clang-format off
	.ops	= &v4l2loopback_ctrl_ops,
	.id	= CID_TIMEOUT_IMAGE_IO,
	.name	= "timeout_image_io",
	.type	= V4L2_CTRL_TYPE_BUTTON,
	.min	= 0,
	.max	= 0,
	.step	= 0,
	.def	= 0,
	// clang-format on
};

/* module structures */
struct v4l2loopback_private {
	int device_nr;
};

/* TODO(vasaka) use typenames which are common to kernel, but first find out if
 * it is needed */
/* struct keeping state and settings of loopback device */

struct v4l2l_buffer {
	struct v4l2_buffer buffer;
	struct list_head list_head;
	atomic_t use_count;
};

struct v4l2_loopback_device {
	struct v4l2_device v4l2_dev;
	struct v4l2_ctrl_handler ctrl_handler;
	struct video_device *vdev;

	/* loopback device-specific parameters */
	char card_label[32];
	bool announce_all_caps; /* announce both OUTPUT and CAPTURE capabilities
				 * when true; else announce OUTPUT when no
				 * writer is streaming, otherwise CAPTURE. */
	int max_openers; /* how many times can this device be opened */
	int min_width, max_width;
	int min_height, max_height;

	/* pixel and stream format */
	struct v4l2_pix_format pix_format;
	bool pix_format_has_valid_sizeimage;
	struct v4l2_captureparm capture_param;
	unsigned long frame_jiffies;

	/* ctrls */
	int keep_format; /* CID_KEEP_FORMAT; lock the format, do not free
			  * on close(), and when `!announce_all_caps` do NOT
			  * fall back to OUTPUT when no writers attached (clear
			  * `keep_format` to attach a new writer) */
	int sustain_framerate; /* CID_SUSTAIN_FRAMERATE; duplicate frames to maintain
				  (close to) nominal framerate */
	unsigned long timeout_jiffies; /* CID_TIMEOUT; 0 means disabled */
	int timeout_image_io; /* CID_TIMEOUT_IMAGE_IO; next opener will
			       * queue/dequeue the timeout image buffer */

	/* buffers for OUTPUT and CAPTURE */
	u8 *image; /* pointer to actual buffers data */
	unsigned long image_size; /* number of bytes alloc'd for all buffers */
	struct v4l2l_buffer buffers[MAX_BUFFERS]; /* inner driver buffers */
	u32 buffer_count; /* should not be big, 4 is a good choice */
	u32 buffer_size; /* number of bytes alloc'd per buffer */
	u32 used_buffer_count; /* number of buffers allocated to openers */
	struct list_head outbufs_list; /* FIFO queue for OUTPUT buffers */
	u32 bufpos2index[MAX_BUFFERS]; /* mapping of `(position % used_buffers)`
					* to `buffers[index]` */
	s64 write_position; /* sequence number of last 'displayed' buffer plus
			     * one */

	/* synchronization between openers */
	atomic_t open_count;
	struct mutex image_mutex; /* mutex for allocating image(s) and
				   * exchanging format tokens */
	spinlock_t lock; /* lock for the timeout and framerate timers */
	spinlock_t list_lock; /* lock for the OUTPUT buffer queue */
	wait_queue_head_t read_event;
	u32 format_tokens; /* tokens to 'set format' for OUTPUT, CAPTURE, or
			    * timeout buffers */
	u32 stream_tokens; /* tokens to 'start' OUTPUT, CAPTURE, or timeout
			    * stream */

	/* sustain framerate */
	struct timer_list sustain_timer;
	unsigned int reread_count;

	/* timeout */
	u8 *timeout_image; /* copied to outgoing buffers when timeout passes */
	struct v4l2l_buffer timeout_buffer;
	u32 timeout_buffer_size; /* number bytes alloc'd for timeout buffer */
	struct timer_list timeout_timer;
	int timeout_happened;
};

enum v4l2l_io_method {
	V4L2L_IO_NONE = 0,
	V4L2L_IO_MMAP = 1,
	V4L2L_IO_FILE = 2,
	V4L2L_IO_TIMEOUT = 3,
};

/* struct keeping state and type of opener */
struct v4l2_loopback_opener {
	u32 format_token; /* token (if any) for type used in call to S_FMT or
			   * REQBUFS */
	u32 stream_token; /* token (if any) for type used in call to STREAMON */
	u32 buffer_count; /* number of buffers (if any) that opener acquired via
			   * REQBUFS */
	s64 read_position; /* sequence number of the next 'captured' frame */
	unsigned int reread_count;
	enum v4l2l_io_method io_method;

	struct v4l2_fh fh;
};

/* this is heavily inspired by the bttv driver found in the linux kernel */
struct v4l2l_format {
	char *name;
	int fourcc; /* video4linux 2 */
	int depth; /* bit/pixel */
	int flags;
};
/* set the v4l2l_format.flags to PLANAR for non-packed formats */
#define FORMAT_FLAGS_PLANAR 0x01
#define FORMAT_FLAGS_COMPRESSED 0x02

#include "v4l2loopback_formats.h"

#ifndef V4L2_TYPE_IS_CAPTURE
#define V4L2_TYPE_IS_CAPTURE(type)                \
	((type) == V4L2_BUF_TYPE_VIDEO_CAPTURE || \
	 (type) == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE)
#endif /* V4L2_TYPE_IS_CAPTURE */
#ifndef V4L2_TYPE_IS_OUTPUT
#define V4L2_TYPE_IS_OUTPUT(type)                \
	((type) == V4L2_BUF_TYPE_VIDEO_OUTPUT || \
	 (type) == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
#endif /* V4L2_TYPE_IS_OUTPUT */

/* token values for privilege to set format or start/stop stream */
#define V4L2L_TOKEN_CAPTURE 0x01
#define V4L2L_TOKEN_OUTPUT 0x02
#define V4L2L_TOKEN_TIMEOUT 0x04
#define V4L2L_TOKEN_MASK \
	(V4L2L_TOKEN_CAPTURE | V4L2L_TOKEN_OUTPUT | V4L2L_TOKEN_TIMEOUT)

/* helpers for token exchange and token status */
#define token_from_type(type) \
	(V4L2_TYPE_IS_CAPTURE(type) ? V4L2L_TOKEN_CAPTURE : V4L2L_TOKEN_OUTPUT)
#define acquire_token(dev, opener, label, token) \
	do {                                     \
		(opener)->label##_token = token; \
		(dev)->label##_tokens &= ~token; \
	} while (0)
#define release_token(dev, opener, label)                         \
	do {                                                      \
		(dev)->label##_tokens |= (opener)->label##_token; \
		(opener)->label##_token = 0;                      \
	} while (0)
#define has_output_token(token) (token & V4L2L_TOKEN_OUTPUT)
#define has_capture_token(token) (token & V4L2L_TOKEN_CAPTURE)
#define has_no_owners(dev) ((~((dev)->format_tokens) & V4L2L_TOKEN_MASK) == 0)
#define has_other_owners(opener, dev) \
	(~((dev)->format_tokens ^ (opener)->format_token) & V4L2L_TOKEN_MASK)
#define need_timeout_buffer(dev, token) \
	((dev)->timeout_jiffies > 0 || (token) & V4L2L_TOKEN_TIMEOUT)

static const unsigned int FORMATS = ARRAY_SIZE(formats);

static char *fourcc2str(unsigned int fourcc, char buf[5])
{
	buf[0] = (fourcc >> 0) & 0xFF;
	buf[1] = (fourcc >> 8) & 0xFF;
	buf[2] = (fourcc >> 16) & 0xFF;
	buf[3] = (fourcc >> 24) & 0xFF;
	buf[4] = 0;

	return buf;
}

static const struct v4l2l_format *format_by_fourcc(int fourcc)
{
	unsigned int i;
	char buf[5];

	for (i = 0; i < FORMATS; i++) {
		if (formats[i].fourcc == fourcc)
			return formats + i;
	}

	dprintk("unsupported format '%4s'\n", fourcc2str(fourcc, buf));
	return NULL;
}

static void pix_format_set_size(struct v4l2_pix_format *f,
				const struct v4l2l_format *fmt,
				unsigned int width, unsigned int height)
{
	f->width = width;
	f->height = height;

	if (fmt->flags & FORMAT_FLAGS_PLANAR) {
		f->bytesperline = width; /* Y plane */
		f->sizeimage = (width * height * fmt->depth) >> 3;
	} else if (fmt->flags & FORMAT_FLAGS_COMPRESSED) {
		/* doesn't make sense for compressed formats */
		f->bytesperline = 0;
		f->sizeimage = (width * height * fmt->depth) >> 3;
	} else {
		f->bytesperline = (width * fmt->depth) >> 3;
		f->sizeimage = height * f->bytesperline;
	}
}

static int v4l2l_fill_format(struct v4l2_format *fmt, const u32 minwidth,
			     const u32 maxwidth, const u32 minheight,
			     const u32 maxheight)
{
	u32 width = fmt->fmt.pix.width, height = fmt->fmt.pix.height;
	u32 pixelformat = fmt->fmt.pix.pixelformat;
	struct v4l2_format fmt0 = *fmt;
	u32 bytesperline = 0, sizeimage = 0;

	if (!width)
		width = V4L2LOOPBACK_SIZE_DEFAULT_WIDTH;
	if (!height)
		height = V4L2LOOPBACK_SIZE_DEFAULT_HEIGHT;
	width = clamp_val(width, minwidth, maxwidth);
	height = clamp_val(height, minheight, maxheight);

	/* sets: width,height,pixelformat,bytesperline,sizeimage */
	if (!(V4L2_TYPE_IS_MULTIPLANAR(fmt0.type))) {
		fmt0.fmt.pix.bytesperline = 0;
		fmt0.fmt.pix.sizeimage = 0;
	}

	if (0) {
		;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 2, 0)
	} else if (!v4l2_fill_pixfmt(&fmt0.fmt.pix, pixelformat, width,
				     height)) {
		;
	} else if (!v4l2_fill_pixfmt_mp(&fmt0.fmt.pix_mp, pixelformat, width,
					height)) {
		;
#endif
	} else {
		const struct v4l2l_format *format =
			format_by_fourcc(pixelformat);
		if (!format)
			return -EINVAL;
		pix_format_set_size(&fmt0.fmt.pix, format, width, height);
		fmt0.fmt.pix.pixelformat = format->fourcc;
	}

	if (V4L2_TYPE_IS_MULTIPLANAR(fmt0.type)) {
		*fmt = fmt0;

		if ((fmt->fmt.pix_mp.colorspace == V4L2_COLORSPACE_DEFAULT) ||
		    (fmt->fmt.pix_mp.colorspace > V4L2_COLORSPACE_DCI_P3))
			fmt->fmt.pix_mp.colorspace = V4L2_COLORSPACE_SRGB;
		if (V4L2_FIELD_ANY == fmt->fmt.pix_mp.field)
			fmt->fmt.pix_mp.field = V4L2_FIELD_NONE;
	} else {
		bytesperline = fmt->fmt.pix.bytesperline;
		sizeimage = fmt->fmt.pix.sizeimage;

		*fmt = fmt0;

		if (!fmt->fmt.pix.bytesperline)
			fmt->fmt.pix.bytesperline = bytesperline;
		if (!fmt->fmt.pix.sizeimage)
			fmt->fmt.pix.sizeimage = sizeimage;

		if ((fmt->fmt.pix.colorspace == V4L2_COLORSPACE_DEFAULT) ||
		    (fmt->fmt.pix.colorspace > V4L2_COLORSPACE_DCI_P3))
			fmt->fmt.pix.colorspace = V4L2_COLORSPACE_SRGB;
		if (V4L2_FIELD_ANY == fmt->fmt.pix.field)
			fmt->fmt.pix.field = V4L2_FIELD_NONE;
	}

	return 0;
}

/* Checks if v4l2l_fill_format() has set a valid, fixed sizeimage val. */
static bool v4l2l_pix_format_has_valid_sizeimage(struct v4l2_format *fmt)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 2, 0)
	const struct v4l2_format_info *info;

	info = v4l2_format_info(fmt->fmt.pix.pixelformat);
	if (info && info->mem_planes == 1)
		return true;
#endif

	return false;
}

static int pix_format_eq(const struct v4l2_pix_format *ref,
			 const struct v4l2_pix_format *tgt, int strict)
{
	/* check if the two formats are equivalent.
	 * ANY fields are handled gracefully
	 */
#define _pix_format_eq0(x)    \
	if (ref->x != tgt->x) \
	result = 0
#define _pix_format_eq1(x, def)                              \
	do {                                                 \
		if ((def != tgt->x) && (ref->x != tgt->x)) { \
			printk(KERN_INFO #x " failed");      \
			result = 0;                          \
		}                                            \
	} while (0)
	int result = 1;
	_pix_format_eq0(width);
	_pix_format_eq0(height);
	_pix_format_eq0(pixelformat);
	if (!strict)
		return result;
	_pix_format_eq1(field, V4L2_FIELD_ANY);
	_pix_format_eq0(bytesperline);
	_pix_format_eq0(sizeimage);
	_pix_format_eq1(colorspace, V4L2_COLORSPACE_DEFAULT);
	return result;
}

static void set_timeperframe(struct v4l2_loopback_device *dev,
			     struct v4l2_fract *tpf)
{
	if (!tpf->denominator && !tpf->numerator) {
		tpf->numerator = 1;
		tpf->denominator = V4L2LOOPBACK_FPS_DEFAULT;
	} else if (tpf->numerator >
		   V4L2LOOPBACK_FRAME_INTERVAL_MAX * tpf->denominator) {
		/* divide-by-zero or greater than maximum interval => min FPS */
		tpf->numerator = V4L2LOOPBACK_FRAME_INTERVAL_MAX;
		tpf->denominator = 1;
	} else if (tpf->numerator * V4L2LOOPBACK_FPS_MAX < tpf->denominator) {
		/* zero or lower than minimum interval => max FPS */
		tpf->numerator = 1;
		tpf->denominator = V4L2LOOPBACK_FPS_MAX;
	}

	dev->capture_param.timeperframe = *tpf;
	dev->frame_jiffies =
		max(1UL, (msecs_to_jiffies(1000) * tpf->numerator) /
				 tpf->denominator);
}

static struct v4l2_loopback_device *v4l2loopback_cd2dev(struct device *cd);

/* device attributes */
/* available via sysfs: /sys/devices/virtual/video4linux/video* */

static ssize_t attr_show_format(struct device *cd,
				struct device_attribute *attr, char *buf)
{
	/* gets the current format as "FOURCC:WxH@f/s", e.g. "YUYV:320x240@1000/30" */
	struct v4l2_loopback_device *dev = v4l2loopback_cd2dev(cd);
	const struct v4l2_fract *tpf;
	char buf4cc[5], buf_fps[32];

	if (!dev || (has_no_owners(dev) && !dev->keep_format))
		return 0;
	tpf = &dev->capture_param.timeperframe;

	fourcc2str(dev->pix_format.pixelformat, buf4cc);
	if (tpf->numerator == 1)
		snprintf(buf_fps, sizeof(buf_fps), "%u", tpf->denominator);
	else
		snprintf(buf_fps, sizeof(buf_fps), "%u/%u", tpf->denominator,
			 tpf->numerator);
	return sprintf(buf, "%4s:%ux%u@%s\n", buf4cc, dev->pix_format.width,
		       dev->pix_format.height, buf_fps);
}

static ssize_t attr_store_format(struct device *cd,
				 struct device_attribute *attr, const char *buf,
				 size_t len)
{
	struct v4l2_loopback_device *dev = v4l2loopback_cd2dev(cd);
	int fps_num = 0, fps_den = 1;

	if (!dev)
		return -ENODEV;

	/* only fps changing is supported */
	if (sscanf(buf, "@%u/%u", &fps_num, &fps_den) > 0) {
		struct v4l2_fract f = { .numerator = fps_den,
					.denominator = fps_num };
		set_timeperframe(dev, &f);
		return len;
	}
	return -EINVAL;
}

static DEVICE_ATTR(format, S_IRUGO | S_IWUSR, attr_show_format,
		   attr_store_format);

static ssize_t attr_show_buffers(struct device *cd,
				 struct device_attribute *attr, char *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_cd2dev(cd);

	if (!dev)
		return -ENODEV;

	return sprintf(buf, "%u\n", dev->used_buffer_count);
}

static DEVICE_ATTR(buffers, S_IRUGO, attr_show_buffers, NULL);

static ssize_t attr_show_maxopeners(struct device *cd,
				    struct device_attribute *attr, char *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_cd2dev(cd);

	if (!dev)
		return -ENODEV;

	return sprintf(buf, "%d\n", dev->max_openers);
}

static ssize_t attr_store_maxopeners(struct device *cd,
				     struct device_attribute *attr,
				     const char *buf, size_t len)
{
	struct v4l2_loopback_device *dev = NULL;
	unsigned long curr = 0;

	if (kstrtoul(buf, 0, &curr))
		return -EINVAL;

	dev = v4l2loopback_cd2dev(cd);
	if (!dev)
		return -ENODEV;

	if (dev->max_openers == curr)
		return len;

	if (curr > __INT_MAX__ || dev->open_count.counter > curr) {
		/* request to limit to less openers as are currently attached to us */
		return -EINVAL;
	}

	dev->max_openers = (int)curr;

	return len;
}

static DEVICE_ATTR(max_openers, S_IRUGO | S_IWUSR, attr_show_maxopeners,
		   attr_store_maxopeners);

static ssize_t attr_show_state(struct device *cd, struct device_attribute *attr,
			       char *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_cd2dev(cd);

	if (!dev)
		return -ENODEV;

	if (!has_output_token(dev->stream_tokens) || dev->keep_format) {
		return sprintf(buf, "capture\n");
	} else
		return sprintf(buf, "output\n");

	return -EAGAIN;
}

static DEVICE_ATTR(state, S_IRUGO, attr_show_state, NULL);

static void v4l2loopback_remove_sysfs(struct video_device *vdev)
{
#define V4L2_SYSFS_DESTROY(x) device_remove_file(&vdev->dev, &dev_attr_##x)

	if (vdev) {
		V4L2_SYSFS_DESTROY(format);
		V4L2_SYSFS_DESTROY(buffers);
		V4L2_SYSFS_DESTROY(max_openers);
		V4L2_SYSFS_DESTROY(state);
		/* ... */
	}
}

static void v4l2loopback_create_sysfs(struct video_device *vdev)
{
	int res = 0;

#define V4L2_SYSFS_CREATE(x)                                 \
	res = device_create_file(&vdev->dev, &dev_attr_##x); \
	if (res < 0)                                         \
	break
	if (!vdev)
		return;
	do {
		V4L2_SYSFS_CREATE(format);
		V4L2_SYSFS_CREATE(buffers);
		V4L2_SYSFS_CREATE(max_openers);
		V4L2_SYSFS_CREATE(state);
		/* ... */
	} while (0);

	if (res >= 0)
		return;
	dev_err(&vdev->dev, "%s error: %d\n", __func__, res);
}

/* Event APIs */

#define V4L2LOOPBACK_EVENT_BASE (V4L2_EVENT_PRIVATE_START)
#define V4L2LOOPBACK_EVENT_OFFSET 0x08E00000
#define V4L2_EVENT_PRI_CLIENT_USAGE \
	(V4L2LOOPBACK_EVENT_BASE + V4L2LOOPBACK_EVENT_OFFSET + 1)

struct v4l2_event_client_usage {
	__u32 count;
};

/* global module data */
/* find a device based on it's device-number (e.g. '3' for /dev/video3) */
struct v4l2loopback_lookup_cb_data {
	int device_nr;
	struct v4l2_loopback_device *device;
};
static int v4l2loopback_lookup_cb(int id, void *ptr, void *data)
{
	struct v4l2_loopback_device *device = ptr;
	struct v4l2loopback_lookup_cb_data *cbdata = data;
	if (cbdata && device && device->vdev) {
		if (device->vdev->num == cbdata->device_nr) {
			cbdata->device = device;
			cbdata->device_nr = id;
			return 1;
		}
	}
	return 0;
}
static int v4l2loopback_lookup(int device_nr,
			       struct v4l2_loopback_device **device)
{
	struct v4l2loopback_lookup_cb_data data = {
		.device_nr = device_nr,
		.device = NULL,
	};
	int err = idr_for_each(&v4l2loopback_index_idr, &v4l2loopback_lookup_cb,
			       &data);
	if (1 == err) {
		if (device)
			*device = data.device;
		return data.device_nr;
	}
	return -ENODEV;
}
#define v4l2loopback_get_vdev_nr(vdev) \
	((struct v4l2loopback_private *)video_get_drvdata(vdev))->device_nr
static struct v4l2_loopback_device *v4l2loopback_cd2dev(struct device *cd)
{
	struct video_device *loopdev = to_video_device(cd);
	int device_nr = v4l2loopback_get_vdev_nr(loopdev);

	return idr_find(&v4l2loopback_index_idr, device_nr);
}

static struct v4l2_loopback_device *v4l2loopback_getdevice(struct file *f)
{
	struct v4l2loopback_private *ptr = video_drvdata(f);
	int nr = ptr->device_nr;

	return idr_find(&v4l2loopback_index_idr, nr);
}

/* forward declarations */
static void client_usage_queue_event(struct video_device *vdev);
static bool any_buffers_mapped(struct v4l2_loopback_device *dev);
static int allocate_buffers(struct v4l2_loopback_device *dev,
			    struct v4l2_pix_format *pix_format);
static void init_buffers(struct v4l2_loopback_device *dev, u32 bytes_used,
			 u32 buffer_size);
static void free_buffers(struct v4l2_loopback_device *dev);
static int allocate_timeout_buffer(struct v4l2_loopback_device *dev);
static void free_timeout_buffer(struct v4l2_loopback_device *dev);
static void check_timers(struct v4l2_loopback_device *dev);
static const struct v4l2_file_operations v4l2_loopback_fops;
static const struct v4l2_ioctl_ops v4l2_loopback_ioctl_ops;

/* V4L2 ioctl caps and params calls */
/* returns device capabilities
 * called on VIDIOC_QUERYCAP
 */
static int vidioc_querycap(struct file *file, void *fh,
			   struct v4l2_capability *cap)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	int device_nr = v4l2loopback_get_vdev_nr(dev->vdev);
	__u32 capabilities = V4L2_CAP_STREAMING | V4L2_CAP_READWRITE;

	strscpy(cap->driver, "v4l2 loopback", sizeof(cap->driver));
	snprintf(cap->card, sizeof(cap->card), "%s", dev->card_label);
	snprintf(cap->bus_info, sizeof(cap->bus_info),
		 "platform:v4l2loopback-%03d", device_nr);

	if (dev->announce_all_caps) {
		capabilities |= V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT;
	} else {
		if (opener->io_method == V4L2L_IO_TIMEOUT ||
		    (has_output_token(dev->stream_tokens) &&
		     !dev->keep_format)) {
			capabilities |= V4L2_CAP_VIDEO_OUTPUT;
		} else
			capabilities |= V4L2_CAP_VIDEO_CAPTURE;
	}

#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 7, 0)
	dev->vdev->device_caps =
#endif /* >=linux-4.7.0 */
		cap->device_caps = cap->capabilities = capabilities;

	cap->capabilities |= V4L2_CAP_DEVICE_CAPS;

	memset(cap->reserved, 0, sizeof(cap->reserved));
	return 0;
}

static int vidioc_enum_framesizes(struct file *file, void *fh,
				  struct v4l2_frmsizeenum *argp)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);

	/* there can be only one... */
	if (argp->index)
		return -EINVAL;

	if (dev->keep_format || has_other_owners(opener, dev)) {
		/* only current frame size supported */
		if (argp->pixel_format != dev->pix_format.pixelformat)
			return -EINVAL;

		argp->type = V4L2_FRMSIZE_TYPE_DISCRETE;

		argp->discrete.width = dev->pix_format.width;
		argp->discrete.height = dev->pix_format.height;
	} else {
		/* return continuous sizes if pixel format is supported */
		if (NULL == format_by_fourcc(argp->pixel_format))
			return -EINVAL;

		if (dev->min_width == dev->max_width &&
		    dev->min_height == dev->max_height) {
			argp->type = V4L2_FRMSIZE_TYPE_DISCRETE;

			argp->discrete.width = dev->min_width;
			argp->discrete.height = dev->min_height;
		} else {
			argp->type = V4L2_FRMSIZE_TYPE_CONTINUOUS;

			argp->stepwise.min_width = dev->min_width;
			argp->stepwise.min_height = dev->min_height;

			argp->stepwise.max_width = dev->max_width;
			argp->stepwise.max_height = dev->max_height;

			argp->stepwise.step_width = 1;
			argp->stepwise.step_height = 1;
		}
	}
	return 0;
}

/* Test if the device is currently 'capable' of the buffer (stream) type when
 * the `exclusive_caps` parameter is set. `keep_format` should lock the format
 * and prevent free of buffers */
static int check_buffer_capability(struct v4l2_loopback_device *dev,
				   struct v4l2_loopback_opener *opener,
				   enum v4l2_buf_type type)
{
	/* short-circuit for (non-compliant) timeout image mode */
	if (opener->io_method == V4L2L_IO_TIMEOUT)
		return 0;
	if (dev->announce_all_caps)
		return (type == V4L2_BUF_TYPE_VIDEO_CAPTURE ||
			type == V4L2_BUF_TYPE_VIDEO_OUTPUT) ?
			       0 :
			       -EINVAL;
	/* CAPTURE if opener has a capture format or a writer is streaming;
	 * else OUTPUT. */
	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		if (!(has_capture_token(opener->format_token) ||
		      !has_output_token(dev->stream_tokens)))
			return -EINVAL;
		break;
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		if (!(has_output_token(opener->format_token) ||
		      has_output_token(dev->stream_tokens)))
			return -EINVAL;
		break;
	default:
		return -EINVAL;
	}
	return 0;
}
/* returns frameinterval (fps) for the set resolution
 * called on VIDIOC_ENUM_FRAMEINTERVALS
 */
static int vidioc_enum_frameintervals(struct file *file, void *fh,
				      struct v4l2_frmivalenum *argp)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);

	/* there can be only one... */
	if (argp->index)
		return -EINVAL;

	if (dev->keep_format || has_other_owners(opener, dev)) {
		/* keep_format also locks the frame rate */
		if (argp->width != dev->pix_format.width ||
		    argp->height != dev->pix_format.height ||
		    argp->pixel_format != dev->pix_format.pixelformat)
			return -EINVAL;

		argp->type = V4L2_FRMIVAL_TYPE_DISCRETE;
		argp->discrete = dev->capture_param.timeperframe;
	} else {
		if (argp->width < dev->min_width ||
		    argp->width > dev->max_width ||
		    argp->height < dev->min_height ||
		    argp->height > dev->max_height ||
		    !format_by_fourcc(argp->pixel_format))
			return -EINVAL;

		argp->type = V4L2_FRMIVAL_TYPE_CONTINUOUS;
		argp->stepwise.min.numerator = 1;
		argp->stepwise.min.denominator = V4L2LOOPBACK_FPS_MAX;
		argp->stepwise.max.numerator = V4L2LOOPBACK_FRAME_INTERVAL_MAX;
		argp->stepwise.max.denominator = 1;
		argp->stepwise.step.numerator = 1;
		argp->stepwise.step.denominator = 1;
	}

	return 0;
}

/* Enumerate device formats
 * Returns:
 * -   EINVAL the index is out of bounds; or if non-zero when format is fixed
 * -   EFAULT unexpected null pointer */
static int vidioc_enum_fmt_vid(struct file *file, void *fh,
			       struct v4l2_fmtdesc *f)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	int fixed = dev->keep_format || has_other_owners(opener, dev);
	const struct v4l2l_format *fmt;

	if (check_buffer_capability(dev, opener, f->type) < 0)
		return -EINVAL;

	if (!(f->index < FORMATS))
		return -EINVAL;
	/* TODO: Support 6.14 V4L2_FMTDESC_FLAG_ENUM_ALL */
	if (fixed && f->index)
		return -EINVAL;

	fmt = fixed ? format_by_fourcc(dev->pix_format.pixelformat) :
		      &formats[f->index];
	if (!fmt)
		return -EFAULT;

	f->flags = 0;
	if (fmt->flags & FORMAT_FLAGS_COMPRESSED)
		f->flags |= V4L2_FMT_FLAG_COMPRESSED;
	snprintf(f->description, sizeof(f->description), fmt->name);
	f->pixelformat = fmt->fourcc;
	return 0;
}

/* Tests (or tries) the format.
 * Returns:
 * -   EINVAL if the buffer type or format is not supported
 */
static int vidioc_try_fmt_vid(struct file *file, void *fh,
			      struct v4l2_format *f)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);

	if (check_buffer_capability(dev, opener, f->type) < 0)
		return -EINVAL;
	if (v4l2l_fill_format(f, dev->min_width, dev->max_width,
			      dev->min_height, dev->max_height) != 0)
		return -EINVAL;
	if (dev->keep_format || has_other_owners(opener, dev))
		/* use existing format - including colorspace info */
		f->fmt.pix = dev->pix_format;

	return 0;
}

/* Sets new format. Fills 'f' argument with the requested or existing format.
 * Side-effect: buffers are allocated for the (returned) format.
 * Returns:
 * -   EINVAL if the type is not supported
 * -   EBUSY if buffers are already allocated
 * TODO: (vasaka) set subregions of input
 */
static int vidioc_s_fmt_vid(struct file *file, void *fh, struct v4l2_format *f)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 token = opener->io_method == V4L2L_IO_TIMEOUT ?
			    V4L2L_TOKEN_TIMEOUT :
			    token_from_type(f->type);
	int changed, result;
	char buf[5];

	result = vidioc_try_fmt_vid(file, fh, f);
	if (result < 0)
		return result;

	if (opener->buffer_count > 0)
		/* must free buffers before format can be set */
		return -EBUSY;

	result = mutex_lock_killable(&dev->image_mutex);
	if (result < 0)
		return result;

	if (opener->format_token)
		release_token(dev, opener, format);
	if (!(dev->format_tokens & token)) {
		result = -EBUSY;
		goto exit_s_fmt_unlock;
	}

	dprintk("S_FMT[%s] %4s:%ux%u size=%u\n",
		V4L2_TYPE_IS_CAPTURE(f->type) ? "CAPTURE" : "OUTPUT",
		fourcc2str(f->fmt.pix.pixelformat, buf), f->fmt.pix.width,
		f->fmt.pix.height, f->fmt.pix.sizeimage);
	changed = !pix_format_eq(&dev->pix_format, &f->fmt.pix, 0);
	if (changed || has_no_owners(dev)) {
		result = allocate_buffers(dev, &f->fmt.pix);
		if (result < 0)
			goto exit_s_fmt_unlock;
	}
	if ((dev->timeout_image && changed) ||
	    (!dev->timeout_image && need_timeout_buffer(dev, token))) {
		result = allocate_timeout_buffer(dev);
		if (result < 0)
			goto exit_s_fmt_free;
	}
	if (changed) {
		dev->pix_format = f->fmt.pix;
		dev->pix_format_has_valid_sizeimage =
			v4l2l_pix_format_has_valid_sizeimage(f);
	}
	acquire_token(dev, opener, format, token);
	if (opener->io_method == V4L2L_IO_TIMEOUT)
		dev->timeout_image_io = 0;
	goto exit_s_fmt_unlock;
exit_s_fmt_free:
	free_buffers(dev);
exit_s_fmt_unlock:
	mutex_unlock(&dev->image_mutex);
	return result;
}

/* ------------------ CAPTURE ----------------------- */
/* ioctl for VIDIOC_ENUM_FMT, _G_FMT, _S_FMT, and _TRY_FMT when buffer type
 * is V4L2_BUF_TYPE_VIDEO_CAPTURE */

static int vidioc_enum_fmt_cap(struct file *file, void *fh,
			       struct v4l2_fmtdesc *f)
{
	return vidioc_enum_fmt_vid(file, fh, f);
}

static int vidioc_g_fmt_cap(struct file *file, void *fh, struct v4l2_format *f)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, f->type) < 0)
		return -EINVAL;
	f->fmt.pix = dev->pix_format;
	return 0;
}

static int vidioc_try_fmt_cap(struct file *file, void *fh,
			      struct v4l2_format *f)
{
	return vidioc_try_fmt_vid(file, fh, f);
}

static int vidioc_s_fmt_cap(struct file *file, void *fh, struct v4l2_format *f)
{
	return vidioc_s_fmt_vid(file, fh, f);
}

/* ------------------ OUTPUT ----------------------- */
/* ioctl for VIDIOC_ENUM_FMT, _G_FMT, _S_FMT, and _TRY_FMT when buffer type
 * is V4L2_BUF_TYPE_VIDEO_OUTPUT */

static int vidioc_enum_fmt_out(struct file *file, void *fh,
			       struct v4l2_fmtdesc *f)
{
	return vidioc_enum_fmt_vid(file, fh, f);
}

static int vidioc_g_fmt_out(struct file *file, void *fh, struct v4l2_format *f)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, f->type) < 0)
		return -EINVAL;
	/*
	 * LATER: this should return the currently valid format
	 * gstreamer doesn't like it, if this returns -EINVAL, as it
	 * then concludes that there is _no_ valid format
	 * CHECK whether this assumption is wrong,
	 * or whether we have to always provide a valid format
	 */
	f->fmt.pix = dev->pix_format;
	return 0;
}

static int vidioc_try_fmt_out(struct file *file, void *fh,
			      struct v4l2_format *f)
{
	return vidioc_try_fmt_vid(file, fh, f);
}

static int vidioc_s_fmt_out(struct file *file, void *fh, struct v4l2_format *f)
{
	return vidioc_s_fmt_vid(file, fh, f);
}

// #define V4L2L_OVERLAY
#ifdef V4L2L_OVERLAY
/* ------------------ OVERLAY ----------------------- */
/* currently unsupported */
/* GSTreamer's v4l2sink is buggy, as it requires the overlay to work
 * while it should only require it, if overlay is requested
 * once the gstreamer element is fixed, remove the overlay dummies
 */
#warning OVERLAY dummies
static int vidioc_g_fmt_overlay(struct file *file, void *priv,
				struct v4l2_format *fmt)
{
	return 0;
}

static int vidioc_s_fmt_overlay(struct file *file, void *priv,
				struct v4l2_format *fmt)
{
	return 0;
}
#endif /* V4L2L_OVERLAY */

/* ------------------ PARAMs ----------------------- */

/* get some data flow parameters, only capability, fps and readbuffers has
 * effect on this driver
 * called on VIDIOC_G_PARM
 */
static int vidioc_g_parm(struct file *file, void *fh,
			 struct v4l2_streamparm *parm)
{
	/* do not care about type of opener, hope these enums would always be
	 * compatible */
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, parm->type) < 0)
		return -EINVAL;
	parm->parm.capture = dev->capture_param;
	return 0;
}

/* get some data flow parameters, only capability, fps and readbuffers has
 * effect on this driver
 * called on VIDIOC_S_PARM
 */
static int vidioc_s_parm(struct file *file, void *fh,
			 struct v4l2_streamparm *parm)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);

	dprintk("S_PARM(frame-time=%u/%u)\n",
		parm->parm.capture.timeperframe.numerator,
		parm->parm.capture.timeperframe.denominator);
	if (check_buffer_capability(dev, opener, parm->type) < 0)
		return -EINVAL;

	switch (parm->type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		set_timeperframe(dev, &parm->parm.capture.timeperframe);
		break;
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		set_timeperframe(dev, &parm->parm.output.timeperframe);
		break;
	default:
		return -EINVAL;
	}

	parm->parm.capture = dev->capture_param;
	return 0;
}

#ifdef V4L2LOOPBACK_WITH_STD
/* sets a tv standard, actually we do not need to handle this any special way
 * added to support effecttv
 * called on VIDIOC_S_STD
 */
static int vidioc_s_std(struct file *file, void *fh, v4l2_std_id *_std)
{
	v4l2_std_id req_std = 0, supported_std = 0;
	const v4l2_std_id all_std = V4L2_STD_ALL, no_std = 0;

	if (_std) {
		req_std = *_std;
		*_std = all_std;
	}

	/* we support everything in V4L2_STD_ALL, but not more... */
	supported_std = (all_std & req_std);
	if (no_std == supported_std)
		return -EINVAL;

	return 0;
}

/* gets a fake video standard
 * called on VIDIOC_G_STD
 */
static int vidioc_g_std(struct file *file, void *fh, v4l2_std_id *norm)
{
	if (norm)
		*norm = V4L2_STD_ALL;
	return 0;
}
/* gets a fake video standard
 * called on VIDIOC_QUERYSTD
 */
static int vidioc_querystd(struct file *file, void *fh, v4l2_std_id *norm)
{
	if (norm)
		*norm = V4L2_STD_ALL;
	return 0;
}
#endif /* V4L2LOOPBACK_WITH_STD */

static int v4l2loopback_set_ctrl(struct v4l2_loopback_device *dev, u32 id,
				 s64 val)
{
	int result = 0;
	switch (id) {
	case CID_KEEP_FORMAT:
		if (val < 0 || val > 1)
			return -EINVAL;
		dev->keep_format = val;
		result = mutex_lock_killable(&dev->image_mutex);
		if (result < 0)
			return result;
		if (!dev->keep_format) {
			if (has_no_owners(dev) && !any_buffers_mapped(dev))
				free_buffers(dev);
		}
		mutex_unlock(&dev->image_mutex);
		break;
	case CID_SUSTAIN_FRAMERATE:
		if (val < 0 || val > 1)
			return -EINVAL;
		spin_lock_bh(&dev->lock);
		dev->sustain_framerate = val;
		check_timers(dev);
		spin_unlock_bh(&dev->lock);
		break;
	case CID_TIMEOUT:
		if (val < 0 || val > MAX_TIMEOUT)
			return -EINVAL;
		if (val > 0) {
			result = mutex_lock_killable(&dev->image_mutex);
			if (result < 0)
				return result;
			/* on-the-fly allocate if device is owned; else
			 * allocate occurs on next S_FMT or REQBUFS */
			if (!has_no_owners(dev))
				result = allocate_timeout_buffer(dev);
			mutex_unlock(&dev->image_mutex);
			if (result < 0) {
				/* disable timeout as buffer not alloc'd */
				spin_lock_bh(&dev->lock);
				dev->timeout_jiffies = 0;
				spin_unlock_bh(&dev->lock);
				return result;
			}
		}
		spin_lock_bh(&dev->lock);
		dev->timeout_jiffies = msecs_to_jiffies(val);
		check_timers(dev);
		spin_unlock_bh(&dev->lock);
		break;
	case CID_TIMEOUT_IMAGE_IO:
		dev->timeout_image_io = 1;
		break;
	default:
		return -EINVAL;
	}
	return 0;
}

static int v4l2loopback_s_ctrl(struct v4l2_ctrl *ctrl)
{
	struct v4l2_loopback_device *dev = container_of(
		ctrl->handler, struct v4l2_loopback_device, ctrl_handler);
	return v4l2loopback_set_ctrl(dev, ctrl->id, ctrl->val);
}

/* returns set of device outputs, in our case there is only one
 * called on VIDIOC_ENUMOUTPUT
 */
static int vidioc_enum_output(struct file *file, void *fh,
			      struct v4l2_output *outp)
{
	__u32 index = outp->index;
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);

	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_OUTPUT))
		return -ENOTTY;
	if (index)
		return -EINVAL;

	/* clear all data (including the reserved fields) */
	memset(outp, 0, sizeof(*outp));

	outp->index = index;
	strscpy(outp->name, "loopback in", sizeof(outp->name));
	outp->type = V4L2_OUTPUT_TYPE_ANALOG;
	outp->audioset = 0;
	outp->modulator = 0;
#ifdef V4L2LOOPBACK_WITH_STD
	outp->std = V4L2_STD_ALL;
#ifdef V4L2_OUT_CAP_STD
	outp->capabilities |= V4L2_OUT_CAP_STD;
#endif /*  V4L2_OUT_CAP_STD */
#endif /* V4L2LOOPBACK_WITH_STD */

	return 0;
}

/* which output is currently active,
 * called on VIDIOC_G_OUTPUT
 */
static int vidioc_g_output(struct file *file, void *fh, unsigned int *index)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_OUTPUT))
		return -ENOTTY;
	if (index)
		*index = 0;
	return 0;
}

/* set output, can make sense if we have more than one video src,
 * called on VIDIOC_S_OUTPUT
 */
static int vidioc_s_output(struct file *file, void *fh, unsigned int index)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_OUTPUT))
		return -ENOTTY;
	return index == 0 ? index : -EINVAL;
}

/* returns set of device inputs, in our case there is only one,
 * but later I may add more
 * called on VIDIOC_ENUMINPUT
 */
static int vidioc_enum_input(struct file *file, void *fh,
			     struct v4l2_input *inp)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	__u32 index = inp->index;

	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_CAPTURE))
		return -ENOTTY;
	if (index)
		return -EINVAL;

	/* clear all data (including the reserved fields) */
	memset(inp, 0, sizeof(*inp));

	inp->index = index;
	strscpy(inp->name, "loopback", sizeof(inp->name));
	inp->type = V4L2_INPUT_TYPE_CAMERA;
	inp->audioset = 0;
	inp->tuner = 0;
	inp->status = 0;

#ifdef V4L2LOOPBACK_WITH_STD
	inp->std = V4L2_STD_ALL;
#ifdef V4L2_IN_CAP_STD
	inp->capabilities |= V4L2_IN_CAP_STD;
#endif
#endif /* V4L2LOOPBACK_WITH_STD */

	if (has_output_token(dev->stream_tokens) && !dev->keep_format)
		/* if no outputs attached; pretend device is powered off */
		inp->status |= V4L2_IN_ST_NO_SIGNAL;

	return 0;
}

/* which input is currently active,
 * called on VIDIOC_G_INPUT
 */
static int vidioc_g_input(struct file *file, void *fh, unsigned int *index)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_CAPTURE))
		return -ENOTTY; /* NOTE: -EAGAIN might be more informative */
	if (index)
		*index = 0;
	return 0;
}

/* set input, can make sense if we have more than one video src,
 * called on VIDIOC_S_INPUT
 */
static int vidioc_s_input(struct file *file, void *fh, unsigned int index)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	if (index != 0)
		return -EINVAL;
	if (check_buffer_capability(dev, opener, V4L2_BUF_TYPE_VIDEO_CAPTURE))
		return -ENOTTY; /* NOTE: -EAGAIN might be more informative */
	return 0;
}

/* --------------- V4L2 ioctl buffer related calls ----------------- */

#define is_allocated(opener, type, index)                                \
	(opener->format_token & (opener->io_method == V4L2L_IO_TIMEOUT ? \
					 V4L2L_TOKEN_TIMEOUT :           \
					 token_from_type(type)) &&       \
	 (index) < (opener)->buffer_count)
#define BUFFER_DEBUG_FMT_STR                                      \
	"buffer#%u @ %p type=%u bytesused=%u length=%u flags=%x " \
	"field=%u timestamp= %lld.%06lldsequence=%u\n"
#define BUFFER_DEBUG_FMT_ARGS(buf)                                         \
	(buf)->index, (buf), (buf)->type, (buf)->bytesused, (buf)->length, \
		(buf)->flags, (buf)->field,                                \
		(long long)(buf)->timestamp.tv_sec,                        \
		(long long)(buf)->timestamp.tv_usec, (buf)->sequence
/* Buffer flag helpers */
#define unset_flags(flags)                      \
	do {                                    \
		flags &= ~V4L2_BUF_FLAG_QUEUED; \
		flags &= ~V4L2_BUF_FLAG_DONE;   \
	} while (0)
#define set_queued(flags)                      \
	do {                                   \
		flags |= V4L2_BUF_FLAG_QUEUED; \
		flags &= ~V4L2_BUF_FLAG_DONE;  \
	} while (0)
#define set_done(flags)                         \
	do {                                    \
		flags &= ~V4L2_BUF_FLAG_QUEUED; \
		flags |= V4L2_BUF_FLAG_DONE;    \
	} while (0)

static bool any_buffers_mapped(struct v4l2_loopback_device *dev)
{
	u32 index;
	for (index = 0; index < dev->buffer_count; ++index)
		if (dev->buffers[index].buffer.flags & V4L2_BUF_FLAG_MAPPED)
			return true;
	return false;
}

static void prepare_buffer_queue(struct v4l2_loopback_device *dev, int count)
{
	struct v4l2l_buffer *bufd, *n;
	u32 pos;

	spin_lock_bh(&dev->list_lock);

	/* ensure sufficient number of buffers in queue */
	for (pos = 0; pos < count; ++pos) {
		bufd = &dev->buffers[pos];
		if (list_empty(&bufd->list_head))
			list_add_tail(&bufd->list_head, &dev->outbufs_list);
	}
	if (list_empty(&dev->outbufs_list))
		goto exit_prepare_queue_unlock;

	/* remove any excess buffers */
	list_for_each_entry_safe(bufd, n, &dev->outbufs_list, list_head) {
		if (bufd->buffer.index >= count)
			list_del_init(&bufd->list_head);
	}

	/* buffers are no longer queued; and `write_position` will correspond
	 * to the first item of `outbufs_list`. */
	pos = v4l2l_mod64(dev->write_position, count);
	list_for_each_entry(bufd, &dev->outbufs_list, list_head) {
		unset_flags(bufd->buffer.flags);
		dev->bufpos2index[pos % count] = bufd->buffer.index;
		++pos;
	}
exit_prepare_queue_unlock:
	spin_unlock_bh(&dev->list_lock);
}

/* forward declaration */
static int vidioc_streamoff(struct file *file, void *fh,
			    enum v4l2_buf_type type);
/* negotiate buffer type
 * only mmap streaming supported
 * called on VIDIOC_REQBUFS
 */
static int vidioc_reqbufs(struct file *file, void *fh,
			  struct v4l2_requestbuffers *reqbuf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 token = opener->io_method == V4L2L_IO_TIMEOUT ?
			    V4L2L_TOKEN_TIMEOUT :
			    token_from_type(reqbuf->type);
	u32 req_count = reqbuf->count;
	int result = 0;

	dprintk("REQBUFS(memory=%u, req_count=%u) and device-bufs=%u/%u "
		"[used/max]\n",
		reqbuf->memory, req_count, dev->used_buffer_count,
		dev->buffer_count);

	switch (reqbuf->memory) {
	case V4L2_MEMORY_MMAP:
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 20, 0)
		reqbuf->capabilities = 0; /* only guarantee MMAP support */
#endif
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 16, 0)
		reqbuf->flags = 0; /* no memory consistency support */
#endif
		break;
	default:
		return -EINVAL;
	}

	if (opener->format_token & ~token)
		/* different (buffer) type already assigned to descriptor by
		 * S_FMT or REQBUFS */
		return -EINVAL;

	MARK();
	result = mutex_lock_killable(&dev->image_mutex);
	if (result < 0)
		return result; /* -EINTR */

	/* CASE queue/dequeue timeout-buffer only: */
	if (opener->format_token & V4L2L_TOKEN_TIMEOUT) {
		opener->buffer_count = req_count;
		if (req_count == 0)
			release_token(dev, opener, format);
		goto exit_reqbufs_unlock;
	}

	MARK();
	/* CASE count is zero: streamoff, free buffers, release their token */
	if (req_count == 0) {
		if (dev->format_tokens & token) {
			acquire_token(dev, opener, format, token);
			opener->io_method = V4L2L_IO_MMAP;
		}
		result = vidioc_streamoff(file, fh, reqbuf->type);
		opener->buffer_count = 0;
		/* undocumented requirement - REQBUFS with count zero should
		 * ALSO release lock on logical stream */
		if (opener->format_token)
			release_token(dev, opener, format);
		if (has_no_owners(dev))
			dev->used_buffer_count = 0;
		goto exit_reqbufs_unlock;
	}

	/* CASE count non-zero: allocate buffers and acquire token for them */
	MARK();
	switch (reqbuf->type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		if (!(dev->format_tokens & token ||
		      opener->format_token & token))
			/* only exclusive ownership for each stream */
			result = -EBUSY;
		break;
	default:
		result = -EINVAL;
	}
	if (result < 0)
		goto exit_reqbufs_unlock;

	if (has_other_owners(opener, dev) && dev->used_buffer_count > 0) {
		/* allow 'allocation' of existing number of buffers */
		req_count = dev->used_buffer_count;
	} else if (any_buffers_mapped(dev)) {
		/* do not allow re-allocation if buffers are mapped */
		result = -EBUSY;
		goto exit_reqbufs_unlock;
	}

	MARK();
	opener->buffer_count = 0;

	if (req_count > dev->buffer_count)
		req_count = dev->buffer_count;

	if (has_no_owners(dev)) {
		result = allocate_buffers(dev, &dev->pix_format);
		if (result < 0)
			goto exit_reqbufs_unlock;
	}
	if (!dev->timeout_image && need_timeout_buffer(dev, token)) {
		result = allocate_timeout_buffer(dev);
		if (result < 0)
			goto exit_reqbufs_unlock;
	}
	acquire_token(dev, opener, format, token);

	MARK();
	switch (opener->io_method) {
	case V4L2L_IO_TIMEOUT:
		dev->timeout_image_io = 0;
		opener->buffer_count = req_count;
		break;
	default:
		opener->io_method = V4L2L_IO_MMAP;
		prepare_buffer_queue(dev, req_count);
		dev->used_buffer_count = opener->buffer_count = req_count;
	}
exit_reqbufs_unlock:
	mutex_unlock(&dev->image_mutex);
	reqbuf->count = opener->buffer_count;
	return result;
}

/* returns buffer asked for;
 * give app as many buffers as it wants, if it less than MAX,
 * but map them in our inner buffers
 * called on VIDIOC_QUERYBUF
 */
static int vidioc_querybuf(struct file *file, void *fh, struct v4l2_buffer *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 type = buf->type;
	u32 index = buf->index;

	if ((type != V4L2_BUF_TYPE_VIDEO_CAPTURE) &&
	    (type != V4L2_BUF_TYPE_VIDEO_OUTPUT))
		return -EINVAL;
	if (!is_allocated(opener, type, index))
		return -EINVAL;

	if (opener->format_token & V4L2L_TOKEN_TIMEOUT) {
		*buf = dev->timeout_buffer.buffer;
		buf->index = index;
	} else
		*buf = dev->buffers[index].buffer;

	buf->type = type;

	if (!(buf->flags & (V4L2_BUF_FLAG_DONE | V4L2_BUF_FLAG_QUEUED))) {
		/* v4l2-compliance requires these to be zero */
		buf->sequence = 0;
		buf->timestamp.tv_sec = buf->timestamp.tv_usec = 0;
	} else if (V4L2_TYPE_IS_CAPTURE(type)) {
		/* guess flags based on sequence values */
		if (buf->sequence >= opener->read_position) {
			set_done(buf->flags);
		} else if (buf->flags & V4L2_BUF_FLAG_DONE) {
			set_queued(buf->flags);
		}
	}
	dprintkrw("QUERYBUF(%s, index=%u) -> " BUFFER_DEBUG_FMT_STR,
		  V4L2_TYPE_IS_CAPTURE(type) ? "CAPTURE" : "OUTPUT", index,
		  BUFFER_DEBUG_FMT_ARGS(buf));
	return 0;
}

static void buffer_written(struct v4l2_loopback_device *dev,
			   struct v4l2l_buffer *buf)
{
	timer_delete_sync(&dev->sustain_timer);
	timer_delete_sync(&dev->timeout_timer);

	spin_lock_bh(&dev->list_lock);
	list_move_tail(&buf->list_head, &dev->outbufs_list);
	spin_unlock_bh(&dev->list_lock);

	spin_lock_bh(&dev->lock);
	dev->bufpos2index[v4l2l_mod64(dev->write_position,
				      dev->used_buffer_count)] =
		buf->buffer.index;
	++dev->write_position;
	dev->reread_count = 0;

	check_timers(dev);
	spin_unlock_bh(&dev->lock);
}

/* put buffer to queue
 * called on VIDIOC_QBUF
 */
static int vidioc_qbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	struct v4l2l_buffer *bufd;
	u32 index = buf->index;
	u32 type = buf->type;

	if (!is_allocated(opener, type, index))
		return -EINVAL;
	bufd = &dev->buffers[index];

	switch (buf->memory) {
	case V4L2_MEMORY_MMAP:
		if (!(bufd->buffer.flags & V4L2_BUF_FLAG_MAPPED))
			dprintkrw("QBUF() unmapped buffer [index=%u]\n", index);
		break;
	default:
		return -EINVAL;
	}

	if (opener->format_token & V4L2L_TOKEN_TIMEOUT) {
		set_queued(buf->flags);
		return 0;
	}

	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		dprintkrw("QBUF(CAPTURE, index=%u) -> " BUFFER_DEBUG_FMT_STR,
			  index, BUFFER_DEBUG_FMT_ARGS(buf));
		set_queued(buf->flags);
		break;
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		dprintkrw("QBUF(OUTPUT, index=%u) -> " BUFFER_DEBUG_FMT_STR,
			  index, BUFFER_DEBUG_FMT_ARGS(buf));
		if (!(bufd->buffer.flags & V4L2_BUF_FLAG_TIMESTAMP_COPY) &&
		    (buf->timestamp.tv_sec == 0 &&
		     buf->timestamp.tv_usec == 0)) {
			v4l2l_get_timestamp(&bufd->buffer);
		} else {
			bufd->buffer.timestamp = buf->timestamp;
			bufd->buffer.flags |= V4L2_BUF_FLAG_TIMESTAMP_COPY;
			bufd->buffer.flags &=
				~V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
		}
		if (dev->pix_format_has_valid_sizeimage) {
			if (buf->bytesused >= dev->pix_format.sizeimage) {
				bufd->buffer.bytesused =
					dev->pix_format.sizeimage;
			} else {
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 5, 0)
				dev_warn_ratelimited(
					&dev->vdev->dev,
#else
				dprintkrw(
#endif
					"warning queued output buffer bytesused too small %u < %u\n",
					buf->bytesused,
					dev->pix_format.sizeimage);
				bufd->buffer.bytesused = buf->bytesused;
			}
		} else {
			bufd->buffer.bytesused = buf->bytesused;
		}
		bufd->buffer.sequence = dev->write_position;
		set_queued(bufd->buffer.flags);
		*buf = bufd->buffer;
		buffer_written(dev, bufd);
		set_done(bufd->buffer.flags);
		wake_up_all(&dev->read_event);
		break;
	default:
		return -EINVAL;
	}
	buf->type = type;
	return 0;
}

static int can_read(struct v4l2_loopback_device *dev,
		    struct v4l2_loopback_opener *opener)
{
	int ret;

	spin_lock_bh(&dev->lock);
	check_timers(dev);
	ret = dev->write_position > opener->read_position ||
	      dev->reread_count > opener->reread_count || dev->timeout_happened;
	spin_unlock_bh(&dev->lock);
	return ret;
}

static int get_capture_buffer(struct file *file)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener =
		v4l2l_f_to_opener(file, file->private_data);
	int pos, timeout_happened;
	u32 index;

	if ((file->f_flags & O_NONBLOCK) &&
	    (dev->write_position <= opener->read_position &&
	     dev->reread_count <= opener->reread_count &&
	     !dev->timeout_happened))
		return -EAGAIN;
	wait_event_interruptible(dev->read_event, can_read(dev, opener));

	spin_lock_bh(&dev->lock);
	if (dev->write_position == opener->read_position) {
		if (dev->reread_count > opener->reread_count + 2)
			opener->reread_count = dev->reread_count - 1;
		++opener->reread_count;
		pos = v4l2l_mod64(opener->read_position +
					  dev->used_buffer_count - 1,
				  dev->used_buffer_count);
	} else {
		opener->reread_count = 0;
		if (dev->write_position >
		    opener->read_position + dev->used_buffer_count)
			opener->read_position = dev->write_position - 1;
		pos = v4l2l_mod64(opener->read_position,
				  dev->used_buffer_count);
		++opener->read_position;
	}
	timeout_happened = dev->timeout_happened && (dev->timeout_jiffies > 0);
	dev->timeout_happened = 0;
	spin_unlock_bh(&dev->lock);

	index = dev->bufpos2index[pos];
	if (timeout_happened) {
		if (index >= dev->used_buffer_count) {
			dprintkrw("get_capture_buffer() read position is at "
				  "an unallocated buffer [index=%u]\n",
				  index);
			return -EFAULT;
		}
		/* although allocated on-demand, timeout_image is freed only
		 * in free_buffers(), so we don't need to worry about it being
		 * deallocated suddenly */
		memcpy(dev->image + dev->buffers[index].buffer.m.offset,
		       dev->timeout_image, dev->buffer_size);
	}
	return (int)index;
}

/* put buffer to dequeue
 * called on VIDIOC_DQBUF
 */
static int vidioc_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 type = buf->type;
	int index;
	struct v4l2l_buffer *bufd;

	if (buf->memory != V4L2_MEMORY_MMAP)
		return -EINVAL;
	if (opener->format_token & V4L2L_TOKEN_TIMEOUT) {
		*buf = dev->timeout_buffer.buffer;
		buf->type = type;
		unset_flags(buf->flags);
		return 0;
	}
	if ((opener->buffer_count == 0) ||
	    !(opener->format_token & token_from_type(type)))
		return -EINVAL;

	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		index = get_capture_buffer(file);
		if (index < 0)
			return index;
		*buf = dev->buffers[index].buffer;
		unset_flags(buf->flags);
		break;
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		spin_lock_bh(&dev->list_lock);

		bufd = list_first_entry_or_null(&dev->outbufs_list,
						struct v4l2l_buffer, list_head);
		if (bufd)
			list_move_tail(&bufd->list_head, &dev->outbufs_list);

		spin_unlock_bh(&dev->list_lock);
		if (!bufd)
			return -EFAULT;
		unset_flags(bufd->buffer.flags);
		*buf = bufd->buffer;
		break;
	default:
		return -EINVAL;
	}

	buf->type = type;
	dprintkrw("DQBUF(%s, index=%u) -> " BUFFER_DEBUG_FMT_STR,
		  V4L2_TYPE_IS_CAPTURE(type) ? "CAPTURE" : "OUTPUT", index,
		  BUFFER_DEBUG_FMT_ARGS(buf));
	return 0;
}

/* ------------- STREAMING ------------------- */

/* start streaming
 * called on VIDIOC_STREAMON
 */
static int vidioc_streamon(struct file *file, void *fh, enum v4l2_buf_type type)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 token = token_from_type(type);

	/* short-circuit when using timeout buffer set */
	if (opener->format_token & V4L2L_TOKEN_TIMEOUT)
		return 0;
	/* opener must have claimed (same) buffer set via REQBUFS */
	if (!opener->buffer_count || !(opener->format_token & token))
		return -EINVAL;

	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		if (has_output_token(dev->stream_tokens) && !dev->keep_format)
			return -EIO;
		if (dev->stream_tokens & token) {
			acquire_token(dev, opener, stream, token);
			client_usage_queue_event(dev->vdev);
		}
		return 0;
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		if (dev->stream_tokens & token)
			acquire_token(dev, opener, stream, token);
		return 0;
	default:
		return -EINVAL;
	}
}

/* stop streaming
 * called on VIDIOC_STREAMOFF
 */
static int vidioc_streamoff(struct file *file, void *fh,
			    enum v4l2_buf_type type)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	u32 token = token_from_type(type);

	/* short-circuit when using timeout buffer set */
	if (opener->format_token & V4L2L_TOKEN_TIMEOUT)
		return 0;
	/* short-circuit when buffer set has no owner */
	if (dev->format_tokens & token)
		return 0;
	/* opener needs a claim to buffer set */
	if (!opener->format_token)
		return -EBUSY;
	if (opener->format_token & ~token)
		return -EINVAL;

	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		if (opener->stream_token & token)
			release_token(dev, opener, stream);
		/* reset output queue */
		if (dev->used_buffer_count > 0)
			prepare_buffer_queue(dev, dev->used_buffer_count);
		return 0;
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		if (opener->stream_token & token) {
			release_token(dev, opener, stream);
			client_usage_queue_event(dev->vdev);
		}
		return 0;
	default:
		return -EINVAL;
	}
}

#ifdef CONFIG_VIDEO_V4L1_COMPAT
static int vidiocgmbuf(struct file *file, void *fh, struct video_mbuf *p)
{
	struct v4l2_loopback_device *dev;
	MARK();

	dev = v4l2loopback_getdevice(file);
	p->frames = dev->buffer_count;
	p->offsets[0] = 0;
	p->offsets[1] = 0;
	p->size = dev->buffer_size;
	return 0;
}
#endif

static void client_usage_queue_event(struct video_device *vdev)
{
	struct v4l2_event ev;
	struct v4l2_loopback_device *dev;

	dev = container_of(vdev->v4l2_dev, struct v4l2_loopback_device,
			   v4l2_dev);

	memset(&ev, 0, sizeof(ev));
	ev.type = V4L2_EVENT_PRI_CLIENT_USAGE;
	((struct v4l2_event_client_usage *)&ev.u)->count =
		!has_capture_token(dev->stream_tokens);

	v4l2_event_queue(vdev, &ev);
}

static int client_usage_ops_add(struct v4l2_subscribed_event *sev,
				unsigned elems)
{
	if (!(sev->flags & V4L2_EVENT_SUB_FL_SEND_INITIAL))
		return 0;

	client_usage_queue_event(sev->fh->vdev);
	return 0;
}

static void client_usage_ops_replace(struct v4l2_event *old,
				     const struct v4l2_event *new)
{
	*((struct v4l2_event_client_usage *)&old->u) =
		*((struct v4l2_event_client_usage *)&new->u);
}

static void client_usage_ops_merge(const struct v4l2_event *old,
				   struct v4l2_event *new)
{
	*((struct v4l2_event_client_usage *)&new->u) =
		*((struct v4l2_event_client_usage *)&old->u);
}

const struct v4l2_subscribed_event_ops client_usage_ops = {
	.add = client_usage_ops_add,
	.replace = client_usage_ops_replace,
	.merge = client_usage_ops_merge,
};

static int vidioc_subscribe_event(struct v4l2_fh *fh,
				  const struct v4l2_event_subscription *sub)
{
	switch (sub->type) {
	case V4L2_EVENT_CTRL:
		return v4l2_ctrl_subscribe_event(fh, sub);
	case V4L2_EVENT_PRI_CLIENT_USAGE:
		return v4l2_event_subscribe(fh, sub, 0, &client_usage_ops);
	}

	return -EINVAL;
}

/* file operations */
static void vm_open(struct vm_area_struct *vma)
{
	struct v4l2l_buffer *buf;
	MARK();

	buf = vma->vm_private_data;
	atomic_inc(&buf->use_count);
	buf->buffer.flags |= V4L2_BUF_FLAG_MAPPED;
}

static void vm_close(struct vm_area_struct *vma)
{
	struct v4l2l_buffer *buf;
	MARK();

	buf = vma->vm_private_data;
	if (atomic_dec_and_test(&buf->use_count))
		buf->buffer.flags &= ~V4L2_BUF_FLAG_MAPPED;
}

static struct vm_operations_struct vm_ops = {
	.open = vm_open,
	.close = vm_close,
};

static int v4l2_loopback_mmap(struct file *file, struct vm_area_struct *vma)
{
	u8 *addr;
	unsigned long start, size, offset;
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener =
		v4l2l_f_to_opener(file, file->private_data);
	struct v4l2l_buffer *buffer = NULL;
	int result = 0;
	MARK();

	offset = (unsigned long)vma->vm_pgoff << PAGE_SHIFT;
	start = (unsigned long)vma->vm_start;
	size = (unsigned long)(vma->vm_end - vma->vm_start); /* always != 0 */

	/* ensure buffer size, count, and allocated image(s) are not altered by
	 * other file descriptors */
	result = mutex_lock_killable(&dev->image_mutex);
	if (result < 0)
		return result;

	if (size > dev->buffer_size) {
		dprintk("mmap() attempt to map %lubytes when %ubytes are "
			"allocated to buffers\n",
			size, dev->buffer_size);
		result = -EINVAL;
		goto exit_mmap_unlock;
	}
	if (offset % dev->buffer_size != 0) {
		dprintk("mmap() offset does not match start of any buffer\n");
		result = -EINVAL;
		goto exit_mmap_unlock;
	}
	switch (opener->format_token) {
	case V4L2L_TOKEN_TIMEOUT:
		if (offset != (unsigned long)dev->buffer_size * MAX_BUFFERS) {
			dprintk("mmap() incorrect offset for timeout image\n");
			result = -EINVAL;
			goto exit_mmap_unlock;
		}
		buffer = &dev->timeout_buffer;
		addr = dev->timeout_image;
		break;
	default:
		if (offset >= dev->image_size) {
			dprintk("mmap() attempt to map beyond all buffers\n");
			result = -EINVAL;
			goto exit_mmap_unlock;
		}
		u32 index = offset / dev->buffer_size;
		buffer = &dev->buffers[index];
		addr = dev->image + offset;
		break;
	}

	while (size > 0) {
		struct page *page = vmalloc_to_page(addr);

		result = vm_insert_page(vma, start, page);
		if (result < 0)
			goto exit_mmap_unlock;

		start += PAGE_SIZE;
		addr += PAGE_SIZE;
		size -= PAGE_SIZE;
	}

	vma->vm_ops = &vm_ops;
	vma->vm_private_data = buffer;

	vm_open(vma);
exit_mmap_unlock:
	mutex_unlock(&dev->image_mutex);
	return result;
}

static unsigned int v4l2_loopback_poll(struct file *file,
				       struct poll_table_struct *pts)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener =
		v4l2l_f_to_opener(file, file->private_data);
	__poll_t req_events = poll_requested_events(pts);
	int ret_mask = 0;

	/* call poll_wait in first call, regardless, to ensure that the
	 * wait-queue is not null */
	poll_wait(file, &dev->read_event, pts);
	poll_wait(file, &opener->fh.wait, pts);

	if (req_events & POLLPRI) {
		if (v4l2_event_pending(&opener->fh)) {
			ret_mask |= POLLPRI;
			if (!(req_events & DEFAULT_POLLMASK))
				return ret_mask;
		}
	}

	switch (opener->format_token) {
	case V4L2L_TOKEN_OUTPUT:
		if (opener->stream_token != 0 ||
		    opener->io_method == V4L2L_IO_NONE)
			ret_mask |= POLLOUT | POLLWRNORM;
		break;
	case V4L2L_TOKEN_CAPTURE:
		if ((opener->io_method == V4L2L_IO_NONE ||
		     opener->stream_token != 0) &&
		    can_read(dev, opener))
			ret_mask |= POLLIN | POLLWRNORM;
		break;
	case V4L2L_TOKEN_TIMEOUT:
		ret_mask |= POLLOUT | POLLWRNORM;
		break;
	default:
		break;
	}

	return ret_mask;
}

/* do not want to limit device opens, it can be as many readers as user want,
 * writers are limited by means of setting writer field */
static int v4l2_loopback_open(struct file *file)
{
	struct v4l2_loopback_device *dev;
	struct v4l2_loopback_opener *opener;

	dev = v4l2loopback_getdevice(file);
	if (dev->open_count.counter >= dev->max_openers)
		return -EBUSY;
	/* kfree on close */
	opener = kzalloc(sizeof(*opener), GFP_KERNEL);
	if (opener == NULL)
		return -ENOMEM;

	atomic_inc(&dev->open_count);
	if (dev->timeout_image_io && dev->format_tokens & V4L2L_TOKEN_TIMEOUT)
		/* will clear timeout_image_io once buffer set acquired */
		opener->io_method = V4L2L_IO_TIMEOUT;

	v4l2_fh_init(&opener->fh, video_devdata(file));
	file->private_data = &opener->fh;

	v4l2_fh_add(&opener->fh, file);
	dprintk("open() -> dev@%p with image@%p\n", dev,
		dev ? dev->image : NULL);
	return 0;
}

static int v4l2_loopback_close(struct file *file)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener =
		v4l2l_f_to_opener(file, file->private_data);
	int result = 0;
	dprintk("close() -> dev@%p with image@%p\n", dev,
		dev ? dev->image : NULL);

	if (opener->format_token) {
		struct v4l2_requestbuffers reqbuf = {
			.count = 0, .memory = V4L2_MEMORY_MMAP, .type = 0
		};
		switch (opener->format_token) {
		case V4L2L_TOKEN_CAPTURE:
			reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
			break;
		case V4L2L_TOKEN_OUTPUT:
		case V4L2L_TOKEN_TIMEOUT:
			reqbuf.type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
			break;
		}
		if (reqbuf.type)
			result = vidioc_reqbufs(file, file->private_data,
						&reqbuf);
		if (result < 0)
			dprintk("failed to free buffers REQBUFS(count=0) "
				" returned %d\n",
				result);
		mutex_lock(&dev->image_mutex);
		release_token(dev, opener, format);
		mutex_unlock(&dev->image_mutex);
	}

	if (atomic_dec_and_test(&dev->open_count)) {
		timer_delete_sync(&dev->sustain_timer);
		timer_delete_sync(&dev->timeout_timer);
		if (!dev->keep_format) {
			mutex_lock(&dev->image_mutex);
			free_buffers(dev);
			mutex_unlock(&dev->image_mutex);
		}
	}

	v4l2_fh_del(&opener->fh, file);
	v4l2_fh_exit(&opener->fh);

	kfree(opener);
	return 0;
}

static int start_fileio(struct file *file, void *fh, enum v4l2_buf_type type)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_loopback_opener *opener = v4l2l_f_to_opener(file, fh);
	struct v4l2_requestbuffers reqbuf = { .count = dev->buffer_count,
					      .memory = V4L2_MEMORY_MMAP,
					      .type = type };
	int token = token_from_type(type);
	int result;

	if (opener->format_token & V4L2L_TOKEN_TIMEOUT ||
	    opener->format_token & ~token)
		return -EBUSY; /* NOTE: -EBADF might be more informative */

	/* short-circuit if already have stream token */
	if (opener->stream_token && opener->io_method == V4L2L_IO_FILE)
		return 0;

	/* otherwise attempt to acquire stream token and assign IO method */
	if (!(dev->stream_tokens & token) || opener->io_method != V4L2L_IO_NONE)
		return -EBUSY;

	result = vidioc_reqbufs(file, fh, &reqbuf);
	if (result < 0)
		return result;
	result = vidioc_streamon(file, fh, type);
	if (result < 0)
		return result;

	opener->io_method = V4L2L_IO_FILE;
	return 0;
}

static ssize_t v4l2_loopback_read(struct file *file, char __user *buf,
				  size_t count, loff_t *ppos)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_buffer *b;
	int index, result;

	dprintkrw("read() %zu bytes\n", count);
	result = start_fileio(file, file->private_data,
			      V4L2_BUF_TYPE_VIDEO_CAPTURE);
	if (result < 0)
		return result;

	index = get_capture_buffer(file);
	if (index < 0)
		return index;
	b = &dev->buffers[index].buffer;
	if (count > b->bytesused)
		count = b->bytesused;
	if (copy_to_user((void *)buf, (void *)(dev->image + b->m.offset),
			 count)) {
		printk(KERN_ERR "v4l2-loopback read() failed copy_to_user()\n");
		return -EFAULT;
	}
	return count;
}

static ssize_t v4l2_loopback_write(struct file *file, const char __user *buf,
				   size_t count, loff_t *ppos)
{
	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
	struct v4l2_buffer *b;
	int index, result;

	dprintkrw("write() %zu bytes\n", count);
	result = start_fileio(file, file->private_data,
			      V4L2_BUF_TYPE_VIDEO_OUTPUT);
	if (result < 0)
		return result;

	if (count > dev->buffer_size)
		count = dev->buffer_size;
	index = v4l2l_mod64(dev->write_position, dev->used_buffer_count);
	b = &dev->buffers[index].buffer;

	if (copy_from_user((void *)(dev->image + b->m.offset), (void *)buf,
			   count)) {
		printk(KERN_ERR
		       "v4l2-loopback write() failed copy_from_user()\n");
		return -EFAULT;
	}
	b->bytesused = count;

	v4l2l_get_timestamp(b);
	b->sequence = dev->write_position;
	set_queued(b->flags);
	buffer_written(dev, &dev->buffers[index]);
	set_done(b->flags);
	wake_up_all(&dev->read_event);

	return count;
}

/* init functions */
/* frees buffers, if allocated */
static void free_buffers(struct v4l2_loopback_device *dev)
{
	dprintk("free_buffers() with image@%p\n", dev->image);
	if (!dev->image)
		return;
	if (!has_no_owners(dev) || any_buffers_mapped(dev))
		/* maybe an opener snuck in before image_mutex was acquired */
		printk(KERN_WARNING
		       "v4l2-loopback free_buffers() buffers of video device "
		       "#%u freed while still mapped to userspace\n",
		       dev->vdev->num);
	vfree(dev->image);
	dev->image = NULL;
	dev->image_size = 0;
	dev->buffer_size = 0;
}

static void free_timeout_buffer(struct v4l2_loopback_device *dev)
{
	dprintk("free_timeout_buffer() with timeout_image@%p\n",
		dev->timeout_image);
	if (!dev->timeout_image)
		return;

	if ((dev->timeout_jiffies > 0 && !has_no_owners(dev)) ||
	    dev->timeout_buffer.buffer.flags & V4L2_BUF_FLAG_MAPPED)
		printk(KERN_WARNING
		       "v4l2-loopback free_timeout_buffer() timeout image "
		       "of device #%u freed while still mapped to userspace\n",
		       dev->vdev->num);

	vfree(dev->timeout_image);
	dev->timeout_image = NULL;
	dev->timeout_buffer_size = 0;
}
/* allocates buffers if no (other) openers are already using them */
static int allocate_buffers(struct v4l2_loopback_device *dev,
			    struct v4l2_pix_format *pix_format)
{
	u32 buffer_size = PAGE_ALIGN(pix_format->sizeimage);
	unsigned long image_size =
		(unsigned long)buffer_size * (unsigned long)dev->buffer_count;
	/* vfree on close file operation in case no open handles left */

	if (buffer_size == 0 || dev->buffer_count == 0 ||
	    buffer_size < pix_format->sizeimage)
		return -EINVAL;

	if ((__LONG_MAX__ / buffer_size) < dev->buffer_count)
		return -ENOSPC;

	dprintk("allocate_buffers() size %lubytes = %ubytes x %ubuffers\n",
		image_size, buffer_size, dev->buffer_count);
	if (dev->image) {
		/* check that no buffers are expected in user-space */
		if (!has_no_owners(dev) || any_buffers_mapped(dev))
			return -EBUSY;
		dprintk("allocate_buffers() existing size=%lubytes\n",
			dev->image_size);
		/* FIXME: prevent double allocation more intelligently! */
		if (image_size == dev->image_size) {
			dprintk("allocate_buffers() keep existing\n");
			return 0;
		}
		free_buffers(dev);
	}

	/* FIXME: set buffers to 0 */
	dev->image = vmalloc(image_size);
	if (dev->image == NULL) {
		dev->buffer_size = dev->image_size = 0;
		return -ENOMEM;
	}
	init_buffers(dev, pix_format->sizeimage, buffer_size);
	dev->buffer_size = buffer_size;
	dev->image_size = image_size;
	dprintk("allocate_buffers() -> vmalloc'd %lubytes\n", dev->image_size);
	return 0;
}
static int allocate_timeout_buffer(struct v4l2_loopback_device *dev)
{
	/* device's `buffer_size` and `buffers` must be initialised in
	 * allocate_buffers() */

	dprintk("allocate_timeout_buffer() size %ubytes\n", dev->buffer_size);
	if (dev->buffer_size == 0)
		return -EINVAL;

	if (dev->timeout_image) {
		if (dev->timeout_buffer.buffer.flags & V4L2_BUF_FLAG_MAPPED)
			return -EBUSY;
		if (dev->buffer_size == dev->timeout_buffer_size)
			return 0;
		free_timeout_buffer(dev);
	}

	dev->timeout_image = vzalloc(dev->buffer_size);
	if (!dev->timeout_image) {
		dev->timeout_buffer_size = 0;
		return -ENOMEM;
	}
	dev->timeout_buffer_size = dev->buffer_size;
	return 0;
}
/* init inner buffers, they are capture mode and flags are set as for capture
 * mode buffers */
static void init_buffers(struct v4l2_loopback_device *dev, u32 bytes_used,
			 u32 buffer_size)
{
	u32 i;

	for (i = 0; i < dev->buffer_count; ++i) {
		struct v4l2_buffer *b = &dev->buffers[i].buffer;
		b->index = i;
		b->bytesused = bytes_used;
		b->length = buffer_size;
		b->field = V4L2_FIELD_NONE;
		b->flags = 0;
		b->m.offset = i * buffer_size;
		b->memory = V4L2_MEMORY_MMAP;
		b->sequence = 0;
		b->timestamp.tv_sec = 0;
		b->timestamp.tv_usec = 0;
		b->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		v4l2l_get_timestamp(b);
	}
	dev->timeout_buffer = dev->buffers[0];
	dev->timeout_buffer.buffer.m.offset = MAX_BUFFERS * buffer_size;
}

/* fills and register video device */
static void init_vdev(struct video_device *vdev, int nr)
{
#ifdef V4L2LOOPBACK_WITH_STD
	vdev->tvnorms = V4L2_STD_ALL;
#endif /* V4L2LOOPBACK_WITH_STD */

	vdev->vfl_type = VFL_TYPE_VIDEO;
	vdev->fops = &v4l2_loopback_fops;
	vdev->ioctl_ops = &v4l2_loopback_ioctl_ops;
	vdev->release = &video_device_release;
	vdev->minor = -1;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 7, 0)
	vdev->device_caps = V4L2_CAP_DEVICE_CAPS | V4L2_CAP_VIDEO_CAPTURE |
			    V4L2_CAP_VIDEO_OUTPUT | V4L2_CAP_READWRITE |
			    V4L2_CAP_STREAMING;
#endif

	if (debug > 1)
		vdev->dev_debug = V4L2_DEV_DEBUG_IOCTL |
				  V4L2_DEV_DEBUG_IOCTL_ARG;

	vdev->vfl_dir = VFL_DIR_M2M;
}

/* init default capture parameters, only fps may be changed in future */
static void init_capture_param(struct v4l2_captureparm *capture_param)
{
	capture_param->capability = V4L2_CAP_TIMEPERFRAME; /* since 2.16 */
	capture_param->capturemode = 0;
	capture_param->extendedmode = 0;
	capture_param->readbuffers = max_buffers;
	capture_param->timeperframe.numerator = 1;
	capture_param->timeperframe.denominator = V4L2LOOPBACK_FPS_DEFAULT;
}

static void check_timers(struct v4l2_loopback_device *dev)
{
	if (has_output_token(dev->stream_tokens))
		return;

	if (dev->timeout_jiffies > 0 && !timer_pending(&dev->timeout_timer))
		mod_timer(&dev->timeout_timer, jiffies + dev->timeout_jiffies);
	if (dev->sustain_framerate && !timer_pending(&dev->sustain_timer))
		mod_timer(&dev->sustain_timer,
			  jiffies + dev->frame_jiffies * 3 / 2);
}
#ifdef HAVE_TIMER_SETUP
static void sustain_timer_clb(struct timer_list *t)
{
	struct v4l2_loopback_device *dev =
		container_of(t, struct v4l2_loopback_device, sustain_timer);
#else
static void sustain_timer_clb(unsigned long nr)
{
	struct v4l2_loopback_device *dev =
		idr_find(&v4l2loopback_index_idr, nr);
#endif
	spin_lock(&dev->lock);
	if (dev->sustain_framerate) {
		dev->reread_count++;
		dprintkrw("sustain_timer_clb() write_pos=%lld reread=%u\n",
			  (long long)dev->write_position, dev->reread_count);
		if (dev->reread_count == 1)
			mod_timer(&dev->sustain_timer,
				  jiffies + max(1UL, dev->frame_jiffies / 2));
		else
			mod_timer(&dev->sustain_timer,
				  jiffies + dev->frame_jiffies);
		wake_up_all(&dev->read_event);
	}
	spin_unlock(&dev->lock);
}
#ifdef HAVE_TIMER_SETUP
static void timeout_timer_clb(struct timer_list *t)
{
	struct v4l2_loopback_device *dev =
		container_of(t, struct v4l2_loopback_device, timeout_timer);
#else
static void timeout_timer_clb(unsigned long nr)
{
	struct v4l2_loopback_device *dev =
		idr_find(&v4l2loopback_index_idr, nr);
#endif
	spin_lock(&dev->lock);
	if (dev->timeout_jiffies > 0) {
		dev->timeout_happened = 1;
		mod_timer(&dev->timeout_timer, jiffies + dev->timeout_jiffies);
		wake_up_all(&dev->read_event);
	}
	spin_unlock(&dev->lock);
}

/* init loopback main structure */
#define DEFAULT_FROM_CONF(confmember, default_condition, default_value)        \
	((conf) ?                                                              \
		 ((conf->confmember default_condition) ? (default_value) :     \
							 (conf->confmember)) : \
		 default_value)

static int v4l2_loopback_add(struct v4l2_loopback_config *conf, int *ret_nr)
{
	struct v4l2_loopback_device *dev;
	struct v4l2_ctrl_handler *hdl;
	struct v4l2loopback_private *vdev_priv = NULL;
	int err;

	u32 _width = V4L2LOOPBACK_SIZE_DEFAULT_WIDTH;
	u32 _height = V4L2LOOPBACK_SIZE_DEFAULT_HEIGHT;

	u32 _min_width = DEFAULT_FROM_CONF(min_width,
					   < V4L2LOOPBACK_SIZE_MIN_WIDTH,
					   V4L2LOOPBACK_SIZE_MIN_WIDTH);
	u32 _min_height = DEFAULT_FROM_CONF(min_height,
					    < V4L2LOOPBACK_SIZE_MIN_HEIGHT,
					    V4L2LOOPBACK_SIZE_MIN_HEIGHT);
	u32 _max_width = DEFAULT_FROM_CONF(max_width, < _min_width, max_width);
	u32 _max_height =
		DEFAULT_FROM_CONF(max_height, < _min_height, max_height);
	bool _announce_all_caps = (conf && conf->announce_all_caps >= 0) ?
					  (bool)(conf->announce_all_caps) :
					  !(V4L2LOOPBACK_DEFAULT_EXCLUSIVECAPS);
	int _max_buffers = DEFAULT_FROM_CONF(max_buffers, <= 0, max_buffers);
	int _max_openers = DEFAULT_FROM_CONF(max_openers, <= 0, max_openers);
	struct v4l2_format _fmt;

	int nr = -1;

	if (conf) {
		const int output_nr = conf->output_nr;
#ifdef SPLIT_DEVICES
		const int capture_nr = conf->capture_nr;
#else
		const int capture_nr = output_nr;
#endif
		if (capture_nr >= 0 && output_nr == capture_nr) {
			nr = output_nr;
		} else if (capture_nr < 0 && output_nr < 0) {
			nr = -1;
		} else if (capture_nr < 0) {
			nr = output_nr;
		} else if (output_nr < 0) {
			nr = capture_nr;
		} else {
			printk(KERN_ERR
			       "v4l2-loopback add() split OUTPUT and CAPTURE "
			       "devices not yet supported.\n");
			printk(KERN_INFO
			       "v4l2-loopback add() both devices must have the "
			       "same number (%d != %d).\n",
			       output_nr, capture_nr);
			return -EINVAL;
		}
	}

	if (idr_find(&v4l2loopback_index_idr, nr))
		return -EEXIST;

	/* initialisation of a new device */
	dprintk("add() creating device #%d\n", nr);
	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		return -ENOMEM;

	/* allocate id, if @id >= 0, we're requesting that specific id */
	if (nr >= 0) {
		err = idr_alloc(&v4l2loopback_index_idr, dev, nr, nr + 1,
				GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&v4l2loopback_index_idr, dev, 0, 0, GFP_KERNEL);
	}
	if (err < 0)
		goto out_free_dev;

	/* register new device */
	MARK();
	nr = err;

	if (conf && conf->card_label[0]) {
		snprintf(dev->card_label, sizeof(dev->card_label), "%s",
			 conf->card_label);
	} else {
		snprintf(dev->card_label, sizeof(dev->card_label),
			 "Dummy video device (0x%04X)", nr);
	}
	snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
		 "v4l2loopback-%03d", nr);

	err = v4l2_device_register(NULL, &dev->v4l2_dev);
	if (err)
		goto out_free_idr;

	/* initialise the _video_ device */
	MARK();
	err = -ENOMEM;
	dev->vdev = video_device_alloc();
	if (dev->vdev == NULL)
		goto out_unregister;

	vdev_priv = kzalloc(sizeof(struct v4l2loopback_private), GFP_KERNEL);
	if (vdev_priv == NULL)
		goto out_unregister;

	video_set_drvdata(dev->vdev, vdev_priv);
	if (video_get_drvdata(dev->vdev) == NULL)
		goto out_unregister;

	snprintf(dev->vdev->name, sizeof(dev->vdev->name), "%s",
		 dev->card_label);
	vdev_priv->device_nr = nr;
	init_vdev(dev->vdev, nr);
	dev->vdev->v4l2_dev = &dev->v4l2_dev;

	/* initialise v4l2-loopback specific parameters */
	MARK();
	dev->announce_all_caps = _announce_all_caps;
	dev->min_width = _min_width;
	dev->min_height = _min_height;
	dev->max_width = _max_width;
	dev->max_height = _max_height;
	dev->max_openers = _max_openers;

	/* set (initial) pixel and stream format */
	_width = clamp_val(_width, _min_width, _max_width);
	_height = clamp_val(_height, _min_height, _max_height);
	_fmt = (struct v4l2_format){
		.type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
		.fmt.pix = { .width = _width,
			     .height = _height,
			     .pixelformat = formats[0].fourcc,
			     .colorspace = V4L2_COLORSPACE_DEFAULT,
			     .field = V4L2_FIELD_NONE }
	};

	err = v4l2l_fill_format(&_fmt, _min_width, _max_width, _min_height,
				_max_height);
	if (err)
		/* highly unexpected failure to assign default format */
		goto out_unregister;
	dev->pix_format = _fmt.fmt.pix;
	init_capture_param(&dev->capture_param);
	set_timeperframe(dev, &dev->capture_param.timeperframe);

	/* ctrls parameters */
	dev->keep_format = 0;
	dev->sustain_framerate = 0;
	dev->timeout_jiffies = 0;
	dev->timeout_image_io = 0;

	/* initialise OUTPUT and CAPTURE buffer values */
	dev->image = NULL;
	dev->image_size = 0;
	dev->buffer_count = _max_buffers;
	dev->buffer_size = 0;
	dev->used_buffer_count = 0;
	INIT_LIST_HEAD(&dev->outbufs_list);
	do {
		u32 index;
		for (index = 0; index < dev->buffer_count; ++index)
			INIT_LIST_HEAD(&dev->buffers[index].list_head);

	} while (0);
	memset(dev->bufpos2index, 0, sizeof(dev->bufpos2index));
	dev->write_position = 0;

	/* initialise synchronisation data */
	atomic_set(&dev->open_count, 0);
	mutex_init(&dev->image_mutex);
	spin_lock_init(&dev->lock);
	spin_lock_init(&dev->list_lock);
	init_waitqueue_head(&dev->read_event);
	dev->format_tokens = V4L2L_TOKEN_MASK;
	dev->stream_tokens = V4L2L_TOKEN_MASK;

	/* initialise sustain frame rate and timeout parameters, and timers */
	dev->reread_count = 0;
	dev->timeout_image = NULL;
	dev->timeout_happened = 0;
#ifdef HAVE_TIMER_SETUP
	timer_setup(&dev->sustain_timer, sustain_timer_clb, 0);
	timer_setup(&dev->timeout_timer, timeout_timer_clb, 0);
#else
	setup_timer(&dev->sustain_timer, sustain_timer_clb, nr);
	setup_timer(&dev->timeout_timer, timeout_timer_clb, nr);
#endif

	/* initialise the control handler and add controls */
	MARK();
	hdl = &dev->ctrl_handler;
	err = v4l2_ctrl_handler_init(hdl, 4);
	if (err)
		goto out_unregister;
	v4l2_ctrl_new_custom(hdl, &v4l2loopback_ctrl_keepformat, NULL);
	v4l2_ctrl_new_custom(hdl, &v4l2loopback_ctrl_sustainframerate, NULL);
	v4l2_ctrl_new_custom(hdl, &v4l2loopback_ctrl_timeout, NULL);
	v4l2_ctrl_new_custom(hdl, &v4l2loopback_ctrl_timeoutimageio, NULL);
	if (hdl->error) {
		err = hdl->error;
		goto out_free_handler;
	}
	dev->v4l2_dev.ctrl_handler = hdl;

	err = v4l2_ctrl_handler_setup(hdl);
	if (err)
		goto out_free_handler;

	/* register the device (creates /dev/video*) */
	MARK();
	if (video_register_device(dev->vdev, VFL_TYPE_VIDEO, nr) < 0) {
		printk(KERN_ERR
		       "v4l2-loopback add() failed video_register_device()\n");
		err = -EFAULT;
		goto out_free_device;
	}
	v4l2loopback_create_sysfs(dev->vdev);
	/* NOTE: ambivalent if sysfs entries fail */

	if (ret_nr)
		*ret_nr = dev->vdev->num;
	return 0;

out_free_device:
out_free_handler:
	v4l2_ctrl_handler_free(&dev->ctrl_handler);
out_unregister:
	if (dev->vdev)
		video_set_drvdata(dev->vdev, NULL);
	video_device_release(dev->vdev);
	if (vdev_priv != NULL)
		kfree(vdev_priv);
	v4l2_device_unregister(&dev->v4l2_dev);
out_free_idr:
	idr_remove(&v4l2loopback_index_idr, nr);
out_free_dev:
	kfree(dev);
	return err;
}

static void v4l2_loopback_remove(struct v4l2_loopback_device *dev)
{
	int device_nr = v4l2loopback_get_vdev_nr(dev->vdev);
	mutex_lock(&dev->image_mutex);
	free_buffers(dev);
	free_timeout_buffer(dev);
	mutex_unlock(&dev->image_mutex);
	v4l2loopback_remove_sysfs(dev->vdev);
	v4l2_ctrl_handler_free(&dev->ctrl_handler);
	kfree(video_get_drvdata(dev->vdev));
	video_unregister_device(dev->vdev);
	v4l2_device_unregister(&dev->v4l2_dev);
	idr_remove(&v4l2loopback_index_idr, device_nr);
	kfree(dev);
}

static long v4l2loopback_control_ioctl(struct file *file, unsigned int cmd,
				       unsigned long parm)
{
	struct v4l2_loopback_device *dev;
	struct v4l2_loopback_config conf;
	struct v4l2_loopback_config *confptr = &conf;
	int device_nr, capture_nr, output_nr;
	int ret;
	const __u32 version = V4L2LOOPBACK_VERSION_CODE;

	ret = mutex_lock_killable(&v4l2loopback_ctl_mutex);
	if (ret)
		return ret;

	ret = -EINVAL;
	switch (cmd) {
	default:
		ret = -ENOSYS;
		break;
		/* add a v4l2loopback device (pair), based on the user-provided specs */
	case V4L2LOOPBACK_CTL_ADD:
	case V4L2LOOPBACK_CTL_ADD_legacy:
		if (parm) {
			if ((ret = copy_from_user(&conf, (void *)parm,
						  sizeof(conf))) < 0)
				break;
		} else
			confptr = NULL;
		ret = v4l2_loopback_add(confptr, &device_nr);
		if (ret >= 0)
			ret = device_nr;
		break;
		/* remove a v4l2loopback device (both capture and output) */
	case V4L2LOOPBACK_CTL_REMOVE:
	case V4L2LOOPBACK_CTL_REMOVE_legacy:
		ret = v4l2loopback_lookup((__u32)parm, &dev);
		if (ret >= 0 && dev) {
			ret = -EBUSY;
			if (dev->open_count.counter > 0)
				break;
			v4l2_loopback_remove(dev);
			ret = 0;
		};
		break;
		/* get information for a loopback device.
		 * this is mostly about limits (which cannot be queried directly with  VIDIOC_G_FMT and friends
		 */
	case V4L2LOOPBACK_CTL_QUERY:
	case V4L2LOOPBACK_CTL_QUERY_legacy:
		if (!parm)
			break;
		if ((ret = copy_from_user(&conf, (void *)parm, sizeof(conf))) <
		    0)
			break;
		capture_nr = output_nr = conf.output_nr;
#ifdef SPLIT_DEVICES
		capture_nr = conf.capture_nr;
#endif
		device_nr = (output_nr < 0) ? capture_nr : output_nr;
		MARK();
		/* get the device from either capture_nr or output_nr (whatever is valid) */
		if ((ret = v4l2loopback_lookup(device_nr, &dev)) < 0)
			break;
		MARK();
		/* if we got the device from output_nr and there is a valid capture_nr,
		 * make sure that both refer to the same device (or bail out)
		 */
		if ((device_nr != capture_nr) && (capture_nr >= 0) &&
		    ((ret = v4l2loopback_lookup(capture_nr, 0)) < 0))
			break;
		MARK();
		/* if otoh, we got the device from capture_nr and there is a valid output_nr,
		 * make sure that both refer to the same device (or bail out)
		 */
		if ((device_nr != output_nr) && (output_nr >= 0) &&
		    ((ret = v4l2loopback_lookup(output_nr, 0)) < 0))
			break;

		/* v4l2_loopback_config identified a single device, so fetch the data */
		snprintf(conf.card_label, sizeof(conf.card_label), "%s",
			 dev->card_label);

		conf.output_nr = dev->vdev->num;
#ifdef SPLIT_DEVICES
		conf.capture_nr = dev->vdev->num;
#endif
		conf.min_width = dev->min_width;
		conf.min_height = dev->min_height;
		conf.max_width = dev->max_width;
		conf.max_height = dev->max_height;
		conf.announce_all_caps = dev->announce_all_caps;
		conf.max_buffers = dev->buffer_count;
		conf.max_openers = dev->max_openers;
		conf.debug = debug;
		MARK();
		if (copy_to_user((void *)parm, &conf, sizeof(conf))) {
			ret = -EFAULT;
			break;
		}
		ret = 0;
		break;
	case V4L2LOOPBACK_CTL_VERSION:
		if (!parm)
			break;
		if (copy_to_user((void *)parm, &version, sizeof(version))) {
			ret = -EFAULT;
			break;
		}
		ret = 0;
		break;
	}

	mutex_unlock(&v4l2loopback_ctl_mutex);
	MARK();
	return ret;
}

/* LINUX KERNEL */

static const struct file_operations v4l2loopback_ctl_fops = {
	// clang-format off
	.owner		= THIS_MODULE,
	.open		= nonseekable_open,
	.unlocked_ioctl	= v4l2loopback_control_ioctl,
	.compat_ioctl	= v4l2loopback_control_ioctl,
	.llseek		= noop_llseek,
	// clang-format on
};

static struct miscdevice v4l2loopback_misc = {
	// clang-format off
	.minor		= MISC_DYNAMIC_MINOR,
	.name		= "v4l2loopback",
	.fops		= &v4l2loopback_ctl_fops,
	// clang-format on
};

static const struct v4l2_file_operations v4l2_loopback_fops = {
	// clang-format off
	.owner		= THIS_MODULE,
	.open		= v4l2_loopback_open,
	.release	= v4l2_loopback_close,
	.read		= v4l2_loopback_read,
	.write		= v4l2_loopback_write,
	.poll		= v4l2_loopback_poll,
	.mmap		= v4l2_loopback_mmap,
	.unlocked_ioctl	= video_ioctl2,
	// clang-format on
};

static const struct v4l2_ioctl_ops v4l2_loopback_ioctl_ops = {
	// clang-format off
	.vidioc_querycap		= &vidioc_querycap,
	.vidioc_enum_framesizes		= &vidioc_enum_framesizes,
	.vidioc_enum_frameintervals	= &vidioc_enum_frameintervals,

	.vidioc_enum_output		= &vidioc_enum_output,
	.vidioc_g_output		= &vidioc_g_output,
	.vidioc_s_output		= &vidioc_s_output,

	.vidioc_enum_input		= &vidioc_enum_input,
	.vidioc_g_input			= &vidioc_g_input,
	.vidioc_s_input			= &vidioc_s_input,

	.vidioc_enum_fmt_vid_cap	= &vidioc_enum_fmt_cap,
	.vidioc_g_fmt_vid_cap		= &vidioc_g_fmt_cap,
	.vidioc_s_fmt_vid_cap		= &vidioc_s_fmt_cap,
	.vidioc_try_fmt_vid_cap		= &vidioc_try_fmt_cap,

	.vidioc_enum_fmt_vid_out	= &vidioc_enum_fmt_out,
	.vidioc_s_fmt_vid_out		= &vidioc_s_fmt_out,
	.vidioc_g_fmt_vid_out		= &vidioc_g_fmt_out,
	.vidioc_try_fmt_vid_out		= &vidioc_try_fmt_out,

#ifdef V4L2L_OVERLAY
	.vidioc_s_fmt_vid_overlay	= &vidioc_s_fmt_overlay,
	.vidioc_g_fmt_vid_overlay	= &vidioc_g_fmt_overlay,
#endif

#ifdef V4L2LOOPBACK_WITH_STD
	.vidioc_s_std			= &vidioc_s_std,
	.vidioc_g_std			= &vidioc_g_std,
	.vidioc_querystd		= &vidioc_querystd,
#endif /* V4L2LOOPBACK_WITH_STD */

	.vidioc_g_parm			= &vidioc_g_parm,
	.vidioc_s_parm			= &vidioc_s_parm,

	.vidioc_reqbufs			= &vidioc_reqbufs,
	.vidioc_querybuf		= &vidioc_querybuf,
	.vidioc_qbuf			= &vidioc_qbuf,
	.vidioc_dqbuf			= &vidioc_dqbuf,

	.vidioc_streamon		= &vidioc_streamon,
	.vidioc_streamoff		= &vidioc_streamoff,

#ifdef CONFIG_VIDEO_V4L1_COMPAT
	.vidiocgmbuf			= &vidiocgmbuf,
#endif

	.vidioc_subscribe_event		= &vidioc_subscribe_event,
	.vidioc_unsubscribe_event	= &v4l2_event_unsubscribe,
	// clang-format on
};

static int free_device_cb(int id, void *ptr, void *data)
{
	struct v4l2_loopback_device *dev = ptr;
	v4l2_loopback_remove(dev);
	return 0;
}
static void free_devices(void)
{
	idr_for_each(&v4l2loopback_index_idr, &free_device_cb, NULL);
	idr_destroy(&v4l2loopback_index_idr);
}

static int __init v4l2loopback_init_module(void)
{
	const u32 min_width = V4L2LOOPBACK_SIZE_MIN_WIDTH;
	const u32 min_height = V4L2LOOPBACK_SIZE_MIN_HEIGHT;
	int err;
	int i;
	MARK();

	err = misc_register(&v4l2loopback_misc);
	if (err < 0)
		return err;

	if (devices < 0) {
		devices = 1;

		/* try guessing the devices from the "video_nr" parameter */
		for (i = MAX_DEVICES - 1; i >= 0; i--) {
			if (video_nr[i] >= 0) {
				devices = i + 1;
				break;
			}
		}
	}

	if (devices > MAX_DEVICES) {
		devices = MAX_DEVICES;
		printk(KERN_INFO
		       "v4l2-loopback init() number of initial devices is "
		       "limited to: %d\n",
		       MAX_DEVICES);
	}

	if (max_buffers > MAX_BUFFERS) {
		max_buffers = MAX_BUFFERS;
		printk(KERN_INFO
		       "v4l2-loopback init() number of buffers is limited "
		       "to: %d\n",
		       MAX_BUFFERS);
	}

	if (max_openers < 0) {
		printk(KERN_INFO
		       "v4l2-loopback init() allowing %d openers rather "
		       "than %d\n",
		       2, max_openers);
		max_openers = 2;
	}

	if (max_width < min_width) {
		max_width = V4L2LOOPBACK_SIZE_DEFAULT_MAX_WIDTH;
		printk(KERN_INFO "v4l2-loopback init() using max_width %d\n",
		       max_width);
	}
	if (max_height < min_height) {
		max_height = V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT;
		printk(KERN_INFO "v4l2-loopback init() using max_height %d\n",
		       max_height);
	}

	for (i = 0; i < devices; i++) {
		struct v4l2_loopback_config cfg = {
			// clang-format off
			.output_nr		= video_nr[i],
#ifdef SPLIT_DEVICES
			.capture_nr		= video_nr[i],
#endif
			.min_width		= min_width,
			.min_height		= min_height,
			.max_width		= max_width,
			.max_height		= max_height,
			.announce_all_caps	= (!exclusive_caps[i]),
			.max_buffers		= max_buffers,
			.max_openers		= max_openers,
			.debug			= debug,
			// clang-format on
		};
		cfg.card_label[0] = 0;
		if (card_label[i])
			snprintf(cfg.card_label, sizeof(cfg.card_label), "%s",
				 card_label[i]);
		err = v4l2_loopback_add(&cfg, 0);
		if (err) {
			free_devices();
			goto error;
		}
	}

	dprintk("module installed\n");

	printk(KERN_INFO "v4l2-loopback driver version %d.%d.%d%s loaded\n",
	       // clang-format off
	       (V4L2LOOPBACK_VERSION_CODE >> 16) & 0xff,
	       (V4L2LOOPBACK_VERSION_CODE >>  8) & 0xff,
	       (V4L2LOOPBACK_VERSION_CODE      ) & 0xff,
#ifdef SNAPSHOT_VERSION
	       " (" __stringify(SNAPSHOT_VERSION) ")"
#else
	       ""
#endif
	       );
	// clang-format on

	return 0;
error:
	misc_deregister(&v4l2loopback_misc);
	return err;
}

static void v4l2loopback_cleanup_module(void)
{
	MARK();
	/* unregister the device -> it deletes /dev/video* */
	free_devices();
	/* and get rid of /dev/v4l2loopback */
	misc_deregister(&v4l2loopback_misc);
	dprintk("module removed\n");
}

MODULE_ALIAS_MISCDEV(MISC_DYNAMIC_MINOR);

module_init(v4l2loopback_init_module);
module_exit(v4l2loopback_cleanup_module);