v4l2: add loopback driver

I've cleaned up the compat stuff for this out of tree driver.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 2736 insertions, 0 deletions

diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
index 331b8e535e5b..490fe104f8b3 100644
--- a/drivers/media/v4l2-core/Kconfig
+++ b/drivers/media/v4l2-core/Kconfig
@@ -67,6 +67,12 @@ config V4L2_FLASH_LED_CLASS
 
 	  When in doubt, say N.
 
+config V4L2_LOOPBACK
+	tristate "V4L2 loopback device"
+	depends on VIDEO_V4L2
+	help
+	  Say Y here to enable the V4L2 loopback device.
+
 config V4L2_FWNODE
 	tristate
 	select V4L2_ASYNC
diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
index 2177b9d63a8f..44cc4a89353a 100644
--- a/drivers/media/v4l2-core/Makefile
+++ b/drivers/media/v4l2-core/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_V4L2_FLASH_LED_CLASS) += v4l2-flash-led-class.o
 obj-$(CONFIG_V4L2_FWNODE) += v4l2-fwnode.o
 obj-$(CONFIG_V4L2_H264) += v4l2-h264.o
 obj-$(CONFIG_V4L2_JPEG_HELPER) += v4l2-jpeg.o
+obj-$(CONFIG_V4L2_LOOPBACK) += v4l2-loopback.o
 obj-$(CONFIG_V4L2_MEM2MEM_DEV) += v4l2-mem2mem.o
 obj-$(CONFIG_V4L2_VP9) += v4l2-vp9.o
 
diff --git a/drivers/media/v4l2-core/v4l2-loopback.c b/drivers/media/v4l2-core/v4l2-loopback.c
new file mode 100644
index 000000000000..6b24a123751b
--- /dev/null
+++ b/drivers/media/v4l2-core/v4l2-loopback.c
@@ -0,0 +1,2729 @@
+/* -*- c-file-style: "linux" -*- */
+/*
+ * v4l2loopback.c  --  video4linux2 loopback driver
+ *
+ * Copyright (C) 2005-2009 Vasily Levin (vasaka@gmail.com)
+ * Copyright (C) 2010-2019 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 <media/v4l2-ioctl.h>
+#include <media/v4l2-common.h>
+#include <media/v4l2-device.h>
+#include <media/v4l2-ctrls.h>
+
+#define V4L2LOOPBACK_VERSION_CODE KERNEL_VERSION(0, 12, 5)
+
+MODULE_DESCRIPTION("V4L2 loopback video device");
+MODULE_AUTHOR("Vasily Levin, "
+	      "IOhannes m zmoelnig <zmoelnig@iem.at>,"
+	      "Stefan Diewald,"
+	      "Anton Novikov"
+	      "et al.");
+MODULE_LICENSE("GPL");
+
+/*
+ * helpers
+ */
+#define STRINGIFY(s) #s
+#define STRINGIFY2(s) STRINGIFY(s)
+
+#define dprintk(fmt, args...)                                                  \
+	do {                                                                   \
+		if (debug > 0) {                                               \
+			printk(KERN_INFO "v4l2-loopback[" STRINGIFY2(          \
+				       __LINE__) "]: " fmt,                    \
+			       ##args);                                        \
+		}                                                              \
+	} while (0)
+
+#define MARK()                                                                 \
+	do {                                                                   \
+		if (debug > 1) {                                               \
+			printk(KERN_INFO "%s:%d[%s]\n", __FILE__, __LINE__,    \
+			       __func__);                                      \
+		}                                                              \
+	} while (0)
+
+#define dprintkrw(fmt, args...)                                                \
+	do {                                                                   \
+		if (debug > 2) {                                               \
+			printk(KERN_INFO "v4l2-loopback[" STRINGIFY2(          \
+				       __LINE__) "]: " fmt,                    \
+			       ##args);                                        \
+		}                                                              \
+	} while (0)
+
+
+#define v4l2l_vzalloc vzalloc
+
+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);
+}
+
+/* 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 8
+#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)");
+
+static int max_buffers = 2;
+module_param(max_buffers, int, S_IRUGO);
+MODULE_PARM_DESC(max_buffers, "how many buffers should be allocated");
+
+/* 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
+ */
+static int max_openers = 10;
+module_param(max_openers, int, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(max_openers, "how many users can open loopback device");
+
+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 every device");
+
+static bool exclusive_caps[MAX_DEVICES] = { [0 ...(MAX_DEVICES - 1)] = 0 };
+module_param_array(exclusive_caps, bool, NULL, 0444);
+/* FIXME: wording */
+MODULE_PARM_DESC(
+	exclusive_caps,
+	"whether to announce OUTPUT/CAPTURE capabilities exclusively or not");
+
+/* format specifications */
+#define V4L2LOOPBACK_SIZE_MIN_WIDTH 48
+#define V4L2LOOPBACK_SIZE_MIN_HEIGHT 32
+#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 frame width");
+static int max_height = V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT;
+module_param(max_height, int, S_IRUGO);
+MODULE_PARM_DESC(max_height, "maximum frame height");
+
+/* 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 = {
+	.ops = &v4l2loopback_ctrl_ops,
+	.id = CID_KEEP_FORMAT,
+	.name = "keep_format",
+	.type = V4L2_CTRL_TYPE_BOOLEAN,
+	.min = 0,
+	.max = 1,
+	.step = 1,
+	.def = 0,
+};
+static const struct v4l2_ctrl_config v4l2loopback_ctrl_sustainframerate = {
+	.ops = &v4l2loopback_ctrl_ops,
+	.id = CID_SUSTAIN_FRAMERATE,
+	.name = "sustain_framerate",
+	.type = V4L2_CTRL_TYPE_BOOLEAN,
+	.min = 0,
+	.max = 1,
+	.step = 1,
+	.def = 0,
+};
+static const struct v4l2_ctrl_config v4l2loopback_ctrl_timeout = {
+	.ops = &v4l2loopback_ctrl_ops,
+	.id = CID_TIMEOUT,
+	.name = "timeout",
+	.type = V4L2_CTRL_TYPE_INTEGER,
+	.min = 0,
+	.max = MAX_TIMEOUT,
+	.step = 1,
+	.def = 0,
+};
+static const struct v4l2_ctrl_config v4l2loopback_ctrl_timeoutimageio = {
+	.ops = &v4l2loopback_ctrl_ops,
+	.id = CID_TIMEOUT_IMAGE_IO,
+	.name = "timeout_image_io",
+	.type = V4L2_CTRL_TYPE_BOOLEAN,
+	.min = 0,
+	.max = 1,
+	.step = 1,
+	.def = 0,
+};
+
+/* module structures */
+struct v4l2loopback_private {
+	int devicenr;
+};
+
+/* 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;
+	int use_count;
+};
+
+struct v4l2_loopback_device {
+	struct v4l2_device v4l2_dev;
+	struct v4l2_ctrl_handler ctrl_handler;
+	struct video_device *vdev;
+	/* pixel and stream format */
+	struct v4l2_pix_format pix_format;
+	struct v4l2_captureparm capture_param;
+	unsigned long frame_jiffies;
+
+	/* ctrls */
+	int keep_format; /* CID_KEEP_FORMAT; stay ready_for_capture even when all
+			    openers close() the device */
+	int sustain_framerate; /* CID_SUSTAIN_FRAMERATE; duplicate frames to maintain
+				  (close to) nominal framerate */
+
+	/* buffers stuff */
+	u8 *image; /* pointer to actual buffers data */
+	unsigned long int imagesize; /* size of buffers data */
+	int buffers_number; /* should not be big, 4 is a good choice */
+	struct v4l2l_buffer buffers[MAX_BUFFERS]; /* inner driver buffers */
+	int used_buffers; /* number of the actually used buffers */
+	int max_openers; /* how many times can this device be opened */
+
+	int write_position; /* number of last written frame + 1 */
+	struct list_head outbufs_list; /* buffers in output DQBUF order */
+	int bufpos2index
+		[MAX_BUFFERS]; /* mapping of (read/write_position % used_buffers)
+                        * to inner buffer index */
+	long buffer_size;
+
+	/* sustain_framerate stuff */
+	struct timer_list sustain_timer;
+	unsigned int reread_count;
+
+	/* timeout stuff */
+	unsigned long timeout_jiffies; /* CID_TIMEOUT; 0 means disabled */
+	int timeout_image_io; /* CID_TIMEOUT_IMAGE_IO; next opener will
+			       * read/write to timeout_image */
+	u8 *timeout_image; /* copy of it will be captured when timeout passes */
+	struct v4l2l_buffer timeout_image_buffer;
+	struct timer_list timeout_timer;
+	int timeout_happened;
+
+	/* sync stuff */
+	atomic_t open_count;
+
+	int ready_for_capture; /* set to true when at least one writer opened
+                                * device and negotiated format */
+	int ready_for_output; /* set to true when no writer is currently attached
+			       * this differs slightly from !ready_for_capture,
+			       * e.g. when using fallback images */
+	int announce_all_caps; /* set to false, if device caps (OUTPUT/CAPTURE)
+                                * should only be announced if the resp. "ready"
+                                * flag is set; default=TRUE */
+
+	wait_queue_head_t read_event;
+	spinlock_t lock;
+};
+
+/* types of opener shows what opener wants to do with loopback */
+enum opener_type {
+	UNNEGOTIATED = 0,
+	READER = 1,
+	WRITER = 2,
+};
+
+/* struct keeping state and type of opener */
+struct v4l2_loopback_opener {
+	enum opener_type type;
+	int vidioc_enum_frameintervals_calls;
+	int read_position; /* number of last processed frame + 1 or
+			    * write_position - 1 if reader went out of sync */
+	unsigned int reread_count;
+	struct v4l2_buffer *buffers;
+	int buffers_number; /* should not be big, 4 is a good choice */
+	int timeout_image_io;
+};
+
+/* 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
+
+static const struct v4l2l_format formats[] = {
+	{
+		.name = "32 bpp RGB, le",
+		.fourcc = V4L2_PIX_FMT_BGR32,
+		.depth = 32,
+		.flags = 0,
+	},
+	{
+		.name = "32 bpp RGB, be",
+		.fourcc = V4L2_PIX_FMT_RGB32,
+		.depth = 32,
+		.flags = 0,
+	},
+	{
+		.name = "24 bpp RGB, le",
+		.fourcc = V4L2_PIX_FMT_BGR24,
+		.depth = 24,
+		.flags = 0,
+	},
+	{
+		.name = "24 bpp RGB, be",
+		.fourcc = V4L2_PIX_FMT_RGB24,
+		.depth = 24,
+		.flags = 0,
+	},
+	{
+		.name = "8 bpp RGB-3-3-2",
+		.fourcc = V4L2_PIX_FMT_RGB332,
+		.depth = 8,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp RGB (xxxxrrrr ggggbbbb)",
+		.fourcc = V4L2_PIX_FMT_RGB444,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp RGB-5-5-5",
+		.fourcc = V4L2_PIX_FMT_RGB555,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp RGB-5-6-5",
+		.fourcc = V4L2_PIX_FMT_RGB565,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp RGB-5-5-5 BE",
+		.fourcc = V4L2_PIX_FMT_RGB555X,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp RGB-5-6-5 BE",
+		.fourcc = V4L2_PIX_FMT_RGB565X,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "18 bpp BGR-6-6-6",
+		.fourcc = V4L2_PIX_FMT_BGR666,
+		.depth = 18,
+		.flags = 0,
+	},
+	{
+		.name = "4:2:2, packed, YUYV",
+		.fourcc = V4L2_PIX_FMT_YUYV,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "4:2:2, packed, UYVY",
+		.fourcc = V4L2_PIX_FMT_UYVY,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "4:2:2, packed YVYU",
+		.fourcc = V4L2_PIX_FMT_YVYU,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "4:2:2, packed VYUY",
+		.fourcc = V4L2_PIX_FMT_VYUY,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "4:2:2, packed YYUV",
+		.fourcc = V4L2_PIX_FMT_YYUV,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "YUV-8-8-8-8",
+		.fourcc = V4L2_PIX_FMT_YUV32,
+		.depth = 32,
+		.flags = 0,
+	},
+	{
+		.name = "8 bpp, Greyscale",
+		.fourcc = V4L2_PIX_FMT_GREY,
+		.depth = 8,
+		.flags = 0,
+	},
+	{
+		.name = "4 bpp Greyscale",
+		.fourcc = V4L2_PIX_FMT_Y4,
+		.depth = 4,
+		.flags = 0,
+	},
+	{
+		.name = "6 bpp Greyscale",
+		.fourcc = V4L2_PIX_FMT_Y6,
+		.depth = 6,
+		.flags = 0,
+	},
+	{
+		.name = "10 bpp Greyscale",
+		.fourcc = V4L2_PIX_FMT_Y10,
+		.depth = 10,
+		.flags = 0,
+	},
+	{
+		.name = "12 bpp Greyscale",
+		.fourcc = V4L2_PIX_FMT_Y12,
+		.depth = 12,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp, Greyscale",
+		.fourcc = V4L2_PIX_FMT_Y16,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp xxxxyyyy uuuuvvvv",
+		.fourcc = V4L2_PIX_FMT_YUV444,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp YUV-5-5-5",
+		.fourcc = V4L2_PIX_FMT_YUV555,
+		.depth = 16,
+		.flags = 0,
+	},
+	{
+		.name = "16 bpp YUV-5-6-5",
+		.fourcc = V4L2_PIX_FMT_YUV565,
+		.depth = 16,
+		.flags = 0,
+	},
+
+	/* bayer formats */
+
+	{
+		.name = "Bayer RGGB 8bit",
+		.fourcc = V4L2_PIX_FMT_SRGGB8,
+		.depth = 8,
+		.flags = 0,
+	},
+	{
+		.name = "Bayer GRBG 8bit",
+		.fourcc = V4L2_PIX_FMT_SGRBG8,
+		.depth = 8,
+		.flags = 0,
+	},
+	{
+		.name = "Bayer GBRG 8bit",
+		.fourcc = V4L2_PIX_FMT_SGBRG8,
+		.depth = 8,
+		.flags = 0,
+	},
+	{
+		.name = "Bayer BA81 8bit",
+		.fourcc = V4L2_PIX_FMT_SBGGR8,
+		.depth = 8,
+		.flags = 0,
+	},
+
+	/* here come the planar formats */
+
+	{
+		.name = "4:1:0, planar, Y-Cr-Cb",
+		.fourcc = V4L2_PIX_FMT_YVU410,
+		.depth = 9,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "4:2:0, planar, Y-Cr-Cb",
+		.fourcc = V4L2_PIX_FMT_YVU420,
+		.depth = 12,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "4:1:0, planar, Y-Cb-Cr",
+		.fourcc = V4L2_PIX_FMT_YUV410,
+		.depth = 9,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "4:2:0, planar, Y-Cb-Cr",
+		.fourcc = V4L2_PIX_FMT_YUV420,
+		.depth = 12,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "16 bpp YVU422 planar",
+		.fourcc = V4L2_PIX_FMT_YUV422P,
+		.depth = 16,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "16 bpp YVU411 planar",
+		.fourcc = V4L2_PIX_FMT_YUV411P,
+		.depth = 16,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "12 bpp YUV 4:1:1",
+		.fourcc = V4L2_PIX_FMT_Y41P,
+		.depth = 12,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+	{
+		.name = "12 bpp Y/CbCr 4:2:0 ",
+		.fourcc = V4L2_PIX_FMT_NV12,
+		.depth = 12,
+		.flags = FORMAT_FLAGS_PLANAR,
+	},
+
+	/* here come the compressed formats */
+
+	{
+		.name = "Motion-JPEG",
+		.fourcc = V4L2_PIX_FMT_MJPEG,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "JFIF JPEG",
+		.fourcc = V4L2_PIX_FMT_JPEG,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "DV1394",
+		.fourcc = V4L2_PIX_FMT_DV,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "MPEG-1/2/4 Multiplexed",
+		.fourcc = V4L2_PIX_FMT_MPEG,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "H264 with start codes",
+		.fourcc = V4L2_PIX_FMT_H264,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "H264 without start codes",
+		.fourcc = V4L2_PIX_FMT_H264_NO_SC,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "H264 MVC",
+		.fourcc = V4L2_PIX_FMT_H264_MVC,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "H263",
+		.fourcc = V4L2_PIX_FMT_H263,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "MPEG-1 ES",
+		.fourcc = V4L2_PIX_FMT_MPEG1,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "MPEG-2 ES",
+		.fourcc = V4L2_PIX_FMT_MPEG2,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "MPEG-4 part 2 ES",
+		.fourcc = V4L2_PIX_FMT_MPEG4,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "Xvid",
+		.fourcc = V4L2_PIX_FMT_XVID,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "SMPTE 421M Annex G compliant stream",
+		.fourcc = V4L2_PIX_FMT_VC1_ANNEX_G,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "SMPTE 421M Annex L compliant stream",
+		.fourcc = V4L2_PIX_FMT_VC1_ANNEX_L,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "VP8",
+		.fourcc = V4L2_PIX_FMT_VP8,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "VP9",
+		.fourcc = V4L2_PIX_FMT_VP9,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+	{
+		.name = "HEVC",
+		.fourcc = V4L2_PIX_FMT_HEVC,
+		.depth = 32,
+		.flags = FORMAT_FLAGS_COMPRESSED,
+	},
+};
+
+static const unsigned int FORMATS = ARRAY_SIZE(formats);
+
+static char *fourcc2str(unsigned int fourcc, char buf[4])
+{
+	buf[0] = (fourcc >> 0) & 0xFF;
+	buf[1] = (fourcc >> 8) & 0xFF;
+	buf[2] = (fourcc >> 16) & 0xFF;
+	buf[3] = (fourcc >> 24) & 0xFF;
+
+	return buf;
+}
+
+static const struct v4l2l_format *format_by_fourcc(int fourcc)
+{
+	unsigned int i;
+
+	for (i = 0; i < FORMATS; i++) {
+		if (formats[i].fourcc == fourcc)
+			return formats + i;
+	}
+
+	dprintk("unsupported format '%c%c%c%c'\n", (fourcc >> 0) & 0xFF,
+		(fourcc >> 8) & 0xFF, (fourcc >> 16) & 0xFF,
+		(fourcc >> 24) & 0xFF);
+	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 set_timeperframe(struct v4l2_loopback_device *dev,
+			    struct v4l2_fract *tpf)
+{
+	if ((tpf->denominator < 1) || (tpf->numerator < 1)) {
+		return -EINVAL;
+	}
+	dev->capture_param.timeperframe = *tpf;
+	dev->frame_jiffies = max(1UL, msecs_to_jiffies(1000) * tpf->numerator /
+					      tpf->denominator);
+	return 0;
+}
+
+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 || !dev->ready_for_capture)
+		return 0;
+	tpf = &dev->capture_param.timeperframe;
+
+	fourcc2str(dev->pix_format.pixelformat, buf4cc);
+	buf4cc[4] = 0;
+	if (tpf->numerator == 1)
+		snprintf(buf_fps, sizeof(buf_fps), "%d", tpf->denominator);
+	else
+		snprintf(buf_fps, sizeof(buf_fps), "%d/%d", tpf->denominator,
+			 tpf->numerator);
+	return sprintf(buf, "%4s:%dx%d@%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;
+
+	/* only fps changing is supported */
+	if (sscanf(buf, "@%d/%d", &fps_num, &fps_den) > 0) {
+		struct v4l2_fract f = { .numerator = fps_den,
+					.denominator = fps_num };
+		int err = 0;
+		if ((err = set_timeperframe(dev, &f)) < 0)
+			return err;
+		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);
+
+	return sprintf(buf, "%d\n", dev->used_buffers);
+}
+
+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);
+
+	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->max_openers == curr)
+		return len;
+
+	if (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 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);
+		/* ... */
+	}
+}
+
+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);
+		/* ... */
+	} while (0);
+
+	if (res >= 0)
+		return;
+	dev_err(&vdev->dev, "%s error: %d\n", __func__, res);
+}
+
+/* global module data */
+struct v4l2_loopback_device *devs[MAX_DEVICES];
+
+static struct v4l2_loopback_device *v4l2loopback_cd2dev(struct device *cd)
+{
+	struct video_device *loopdev = to_video_device(cd);
+	struct v4l2loopback_private *ptr =
+		(struct v4l2loopback_private *)video_get_drvdata(loopdev);
+	int nr = ptr->devicenr;
+
+	if (nr < 0 || nr >= devices) {
+		printk(KERN_ERR "v4l2-loopback: illegal device %d\n", nr);
+		return NULL;
+	}
+	return devs[nr];
+}
+
+static struct v4l2_loopback_device *v4l2loopback_getdevice(struct file *f)
+{
+	struct video_device *loopdev = video_devdata(f);
+	struct v4l2loopback_private *ptr =
+		(struct v4l2loopback_private *)video_get_drvdata(loopdev);
+	int nr = ptr->devicenr;
+
+	if (nr < 0 || nr >= devices) {
+		printk(KERN_ERR "v4l2-loopback: illegal device %d\n", nr);
+		return NULL;
+	}
+	return devs[nr];
+}
+
+/* forward declarations */
+static void init_buffers(struct v4l2_loopback_device *dev);
+static int allocate_buffers(struct v4l2_loopback_device *dev);
+static int free_buffers(struct v4l2_loopback_device *dev);
+static void try_free_buffers(struct v4l2_loopback_device *dev);
+static int allocate_timeout_image(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;
+
+/* Queue helpers */
+/* next functions sets buffer flags and adjusts counters accordingly */
+static inline void set_done(struct v4l2l_buffer *buffer)
+{
+	buffer->buffer.flags &= ~V4L2_BUF_FLAG_QUEUED;
+	buffer->buffer.flags |= V4L2_BUF_FLAG_DONE;
+}
+
+static inline void set_queued(struct v4l2l_buffer *buffer)
+{
+	buffer->buffer.flags &= ~V4L2_BUF_FLAG_DONE;
+	buffer->buffer.flags |= V4L2_BUF_FLAG_QUEUED;
+}
+
+static inline void unset_flags(struct v4l2l_buffer *buffer)
+{
+	buffer->buffer.flags &= ~V4L2_BUF_FLAG_QUEUED;
+	buffer->buffer.flags &= ~V4L2_BUF_FLAG_DONE;
+}
+
+static void vidioc_fill_name(char *buf, int len, int nr)
+{
+	if (card_label[nr] != NULL) {
+		snprintf(buf, len, card_label[nr]);
+	} else {
+		snprintf(buf, len, "Dummy video device (0x%04X)", nr);
+	}
+}
+
+/* V4L2 ioctl caps and params calls */
+/* returns device capabilities
+ * called on VIDIOC_QUERYCAP
+ */
+static int vidioc_querycap(struct file *file, void *priv,
+			   struct v4l2_capability *cap)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	int devnr =
+		((struct v4l2loopback_private *)video_get_drvdata(dev->vdev))
+			->devicenr;
+	__u32 capabilities = V4L2_CAP_STREAMING | V4L2_CAP_READWRITE;
+
+	strlcpy(cap->driver, "v4l2 loopback", sizeof(cap->driver));
+	vidioc_fill_name(cap->card, sizeof(cap->card), devnr);
+	snprintf(cap->bus_info, sizeof(cap->bus_info),
+		 "platform:v4l2loopback-%03d", devnr);
+
+	capabilities |= V4L2_CAP_VIDEO_M2M;
+
+	if (dev->announce_all_caps) {
+		capabilities |= V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT;
+	} else {
+		if (dev->ready_for_capture) {
+			capabilities |= V4L2_CAP_VIDEO_CAPTURE;
+		}
+		if (dev->ready_for_output) {
+			capabilities |= V4L2_CAP_VIDEO_OUTPUT;
+		}
+	}
+
+	dev->vdev->device_caps =
+		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;
+
+	/* LATER: what does the index really  mean?
+	 * if it's about enumerating formats, we can safely ignore it
+	 * (CHECK)
+	 */
+
+	/* there can be only one... */
+	if (argp->index)
+		return -EINVAL;
+
+	dev = v4l2loopback_getdevice(file);
+	if (dev->ready_for_capture) {
+		/* format has already been negotiated
+		 * cannot change during runtime
+		 */
+		argp->type = V4L2_FRMSIZE_TYPE_DISCRETE;
+
+		argp->discrete.width = dev->pix_format.width;
+		argp->discrete.height = dev->pix_format.height;
+	} else {
+		/* if the format has not been negotiated yet, we accept anything
+		 */
+		argp->type = V4L2_FRMSIZE_TYPE_CONTINUOUS;
+
+		argp->stepwise.min_width = V4L2LOOPBACK_SIZE_MIN_WIDTH;
+		argp->stepwise.min_height = V4L2LOOPBACK_SIZE_MIN_HEIGHT;
+
+		argp->stepwise.max_width = max_width;
+		argp->stepwise.max_height = max_height;
+
+		argp->stepwise.step_width = 1;
+		argp->stepwise.step_height = 1;
+	}
+	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 = file->private_data;
+
+	if (dev->ready_for_capture) {
+		if (opener->vidioc_enum_frameintervals_calls > 0)
+			return -EINVAL;
+		if (argp->width == dev->pix_format.width &&
+		    argp->height == dev->pix_format.height) {
+			argp->type = V4L2_FRMIVAL_TYPE_DISCRETE;
+			argp->discrete = dev->capture_param.timeperframe;
+			opener->vidioc_enum_frameintervals_calls++;
+			return 0;
+		}
+		return -EINVAL;
+	}
+	return 0;
+}
+
+/* ------------------ CAPTURE ----------------------- */
+
+/* returns device formats
+ * called on VIDIOC_ENUM_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE
+ */
+static int vidioc_enum_fmt_cap(struct file *file, void *fh,
+			       struct v4l2_fmtdesc *f)
+{
+	struct v4l2_loopback_device *dev;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	if (f->index)
+		return -EINVAL;
+	if (dev->ready_for_capture) {
+		const __u32 format = dev->pix_format.pixelformat;
+
+		snprintf(f->description, sizeof(f->description), "[%c%c%c%c]",
+			 (format >> 0) & 0xFF, (format >> 8) & 0xFF,
+			 (format >> 16) & 0xFF, (format >> 24) & 0xFF);
+
+		f->pixelformat = dev->pix_format.pixelformat;
+	} else {
+		return -EINVAL;
+	}
+	f->flags = 0;
+	MARK();
+	return 0;
+}
+
+/* returns current video format format fmt
+ * called on VIDIOC_G_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE
+ */
+static int vidioc_g_fmt_cap(struct file *file, void *priv,
+			    struct v4l2_format *fmt)
+{
+	struct v4l2_loopback_device *dev;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	if (!dev->ready_for_capture)
+		return -EINVAL;
+
+	fmt->fmt.pix = dev->pix_format;
+	MARK();
+	return 0;
+}
+
+/* checks if it is OK to change to format fmt;
+ * actual check is done by inner_try_fmt_cap
+ * just checking that pixelformat is OK and set other parameters, app should
+ * obey this decision
+ * called on VIDIOC_TRY_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE
+ */
+static int vidioc_try_fmt_cap(struct file *file, void *priv,
+			      struct v4l2_format *fmt)
+{
+	struct v4l2_loopback_device *dev;
+	char buf[5];
+
+	dev = v4l2loopback_getdevice(file);
+
+	if (0 == dev->ready_for_capture) {
+		dprintk("setting fmt_cap not possible yet\n");
+		return -EBUSY;
+	}
+
+	if (fmt->fmt.pix.pixelformat != dev->pix_format.pixelformat)
+		return -EINVAL;
+
+	fmt->fmt.pix = dev->pix_format;
+
+	buf[4] = 0;
+	dprintk("capFOURCC=%s\n", fourcc2str(dev->pix_format.pixelformat, buf));
+	return 0;
+}
+
+/* sets new output format, if possible
+ * actually format is set  by input and we even do not check it, just return
+ * current one, but it is possible to set subregions of input TODO(vasaka)
+ * called on VIDIOC_S_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE
+ */
+static int vidioc_s_fmt_cap(struct file *file, void *priv,
+			    struct v4l2_format *fmt)
+{
+	return vidioc_try_fmt_cap(file, priv, fmt);
+}
+
+/* ------------------ OUTPUT ----------------------- */
+
+/* returns device formats;
+ * LATER: allow all formats
+ * called on VIDIOC_ENUM_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT
+ */
+static int vidioc_enum_fmt_out(struct file *file, void *fh,
+			       struct v4l2_fmtdesc *f)
+{
+	struct v4l2_loopback_device *dev;
+	const struct v4l2l_format *fmt;
+
+	dev = v4l2loopback_getdevice(file);
+
+	if (dev->ready_for_capture) {
+		const __u32 format = dev->pix_format.pixelformat;
+
+		/* format has been fixed by the writer, so only one single format is supported */
+		if (f->index)
+			return -EINVAL;
+
+		fmt = format_by_fourcc(format);
+		if (NULL == fmt)
+			return -EINVAL;
+
+		f->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+		/* f->flags = ??; */
+		snprintf(f->description, sizeof(f->description), "%s",
+			 fmt->name);
+
+		f->pixelformat = dev->pix_format.pixelformat;
+	} else {
+		/* fill in a dummy format */
+		/* coverity[unsigned_compare] */
+		if (f->index < 0 || f->index >= FORMATS)
+			return -EINVAL;
+
+		fmt = &formats[f->index];
+
+		f->pixelformat = fmt->fourcc;
+		snprintf(f->description, sizeof(f->description), "%s",
+			 fmt->name);
+	}
+	f->flags = 0;
+
+	return 0;
+}
+
+/* returns current video format format fmt */
+/* NOTE: this is called from the producer
+ * so if format has not been negotiated yet,
+ * it should return ALL of available formats,
+ * called on VIDIOC_G_FMT, with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT
+ */
+static int vidioc_g_fmt_out(struct file *file, void *priv,
+			    struct v4l2_format *fmt)
+{
+	struct v4l2_loopback_device *dev;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	/*
+	 * 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
+	 */
+
+	fmt->fmt.pix = dev->pix_format;
+	return 0;
+}
+
+/* checks if it is OK to change to format fmt;
+ * if format is negotiated do not change it
+ * called on VIDIOC_TRY_FMT with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT
+ */
+static int vidioc_try_fmt_out(struct file *file, void *priv,
+			      struct v4l2_format *fmt)
+{
+	struct v4l2_loopback_device *dev;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	/* TODO(vasaka) loopback does not care about formats writer want to set,
+	 * maybe it is a good idea to restrict format somehow */
+	if (dev->ready_for_capture) {
+		fmt->fmt.pix = dev->pix_format;
+	} else {
+		__u32 w = fmt->fmt.pix.width;
+		__u32 h = fmt->fmt.pix.height;
+		__u32 pixfmt = fmt->fmt.pix.pixelformat;
+		const struct v4l2l_format *format = format_by_fourcc(pixfmt);
+
+		if (w > max_width)
+			w = max_width;
+		if (h > max_height)
+			h = max_height;
+
+		dprintk("trying image %dx%d\n", w, h);
+
+		if (w < 1)
+			w = V4L2LOOPBACK_SIZE_DEFAULT_WIDTH;
+
+		if (h < 1)
+			h = V4L2LOOPBACK_SIZE_DEFAULT_HEIGHT;
+
+		if (NULL == format)
+			format = &formats[0];
+
+		pix_format_set_size(&fmt->fmt.pix, format, w, h);
+
+		fmt->fmt.pix.pixelformat = format->fourcc;
+		fmt->fmt.pix.colorspace = V4L2_COLORSPACE_SRGB;
+
+		if (V4L2_FIELD_ANY == fmt->fmt.pix.field)
+			fmt->fmt.pix.field = V4L2_FIELD_NONE;
+
+		/* FIXME: try_fmt should never modify the device-state */
+		dev->pix_format = fmt->fmt.pix;
+	}
+	return 0;
+}
+
+/* sets new output format, if possible;
+ * allocate data here because we do not know if it will be streaming or
+ * read/write IO
+ * called on VIDIOC_S_FMT with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT
+ */
+static int vidioc_s_fmt_out(struct file *file, void *priv,
+			    struct v4l2_format *fmt)
+{
+	struct v4l2_loopback_device *dev;
+	char buf[5];
+	int ret;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+	ret = vidioc_try_fmt_out(file, priv, fmt);
+
+	dprintk("s_fmt_out(%d) %d...%d\n", ret, dev->ready_for_capture,
+		dev->pix_format.sizeimage);
+
+	buf[4] = 0;
+	dprintk("outFOURCC=%s\n", fourcc2str(dev->pix_format.pixelformat, buf));
+
+	if (ret < 0)
+		return ret;
+
+	if (!dev->ready_for_capture) {
+		dev->buffer_size = PAGE_ALIGN(dev->pix_format.sizeimage);
+		fmt->fmt.pix.sizeimage = dev->buffer_size;
+		allocate_buffers(dev);
+	}
+	return ret;
+}
+
+/*#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 *priv,
+			 struct v4l2_streamparm *parm)
+{
+	/* do not care about type of opener, hope this enums would always be
+	 * compatible */
+	struct v4l2_loopback_device *dev;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+	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 *priv,
+			 struct v4l2_streamparm *parm)
+{
+	struct v4l2_loopback_device *dev;
+	int err = 0;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+	dprintk("vidioc_s_parm called frate=%d/%d\n",
+		parm->parm.capture.timeperframe.numerator,
+		parm->parm.capture.timeperframe.denominator);
+
+	switch (parm->type) {
+	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
+		if ((err = set_timeperframe(
+			     dev, &parm->parm.capture.timeperframe)) < 0)
+			return err;
+		break;
+	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
+		if ((err = set_timeperframe(
+			     dev, &parm->parm.capture.timeperframe)) < 0)
+			return err;
+		break;
+	default:
+		return -1;
+	}
+
+	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 *private_data,
+			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 *private_data,
+			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 *private_data,
+			   v4l2_std_id *norm)
+{
+	if (norm)
+		*norm = V4L2_STD_ALL;
+	return 0;
+}
+#endif /* V4L2LOOPBACK_WITH_STD */
+
+/* get ctrls info
+ * called on VIDIOC_QUERYCTRL
+ */
+static int vidioc_queryctrl(struct file *file, void *fh,
+			    struct v4l2_queryctrl *q)
+{
+	const struct v4l2_ctrl_config *cnf = 0;
+	switch (q->id) {
+	case CID_KEEP_FORMAT:
+		cnf = &v4l2loopback_ctrl_keepformat;
+		break;
+	case CID_SUSTAIN_FRAMERATE:
+		cnf = &v4l2loopback_ctrl_sustainframerate;
+		break;
+	case CID_TIMEOUT:
+		cnf = &v4l2loopback_ctrl_timeout;
+		break;
+	case CID_TIMEOUT_IMAGE_IO:
+		cnf = &v4l2loopback_ctrl_timeoutimageio;
+		break;
+	default:
+		return -EINVAL;
+	}
+	if (!cnf)
+		BUG();
+
+	strcpy(q->name, cnf->name);
+	q->default_value = cnf->def;
+	q->type = cnf->type;
+	q->minimum = cnf->min;
+	q->maximum = cnf->max;
+	q->step = cnf->step;
+
+	memset(q->reserved, 0, sizeof(q->reserved));
+	return 0;
+}
+
+static int vidioc_g_ctrl(struct file *file, void *fh, struct v4l2_control *c)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+
+	switch (c->id) {
+	case CID_KEEP_FORMAT:
+		c->value = dev->keep_format;
+		break;
+	case CID_SUSTAIN_FRAMERATE:
+		c->value = dev->sustain_framerate;
+		break;
+	case CID_TIMEOUT:
+		c->value = jiffies_to_msecs(dev->timeout_jiffies);
+		break;
+	case CID_TIMEOUT_IMAGE_IO:
+		c->value = dev->timeout_image_io;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int v4l2loopback_set_ctrl(struct v4l2_loopback_device *dev, u32 id,
+				 s64 val)
+{
+	switch (id) {
+	case CID_KEEP_FORMAT:
+		if (val < 0 || val > 1)
+			return -EINVAL;
+		dev->keep_format = val;
+		try_free_buffers(dev);
+		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;
+		spin_lock_bh(&dev->lock);
+		dev->timeout_jiffies = msecs_to_jiffies(val);
+		check_timers(dev);
+		spin_unlock_bh(&dev->lock);
+		allocate_timeout_image(dev);
+		break;
+	case CID_TIMEOUT_IMAGE_IO:
+		if (val < 0 || val > 1)
+			return -EINVAL;
+		dev->timeout_image_io = val;
+		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);
+}
+static int vidioc_s_ctrl(struct file *file, void *fh, struct v4l2_control *c)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	return v4l2loopback_set_ctrl(dev, c->id, c->value);
+}
+
+/* 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);
+	MARK();
+
+	if (!dev->announce_all_caps && !dev->ready_for_output)
+		return -ENOTTY;
+
+	if (0 != index)
+		return -EINVAL;
+
+	/* clear all data (including the reserved fields) */
+	memset(outp, 0, sizeof(*outp));
+
+	outp->index = index;
+	strlcpy(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;
+	outp->capabilities |= 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 *i)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	if (!dev->announce_all_caps && !dev->ready_for_output)
+		return -ENOTTY;
+	if (i)
+		*i = 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 i)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	if (!dev->announce_all_caps && !dev->ready_for_output)
+		return -ENOTTY;
+
+	if (i)
+		return -EINVAL;
+
+	return 0;
+}
+
+/* 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)
+{
+	__u32 index = inp->index;
+	MARK();
+
+	if (0 != index)
+		return -EINVAL;
+
+	/* clear all data (including the reserved fields) */
+	memset(inp, 0, sizeof(*inp));
+
+	inp->index = index;
+	strlcpy(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;
+	inp->capabilities |= V4L2_IN_CAP_STD;
+#endif /* V4L2LOOPBACK_WITH_STD */
+
+	return 0;
+}
+
+/* which input is currently active,
+ * called on VIDIOC_G_INPUT
+ */
+static int vidioc_g_input(struct file *file, void *fh, unsigned int *i)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	if (!dev->announce_all_caps && !dev->ready_for_capture)
+		return -ENOTTY;
+	if (i)
+		*i = 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 i)
+{
+	struct v4l2_loopback_device *dev = v4l2loopback_getdevice(file);
+	if (!dev->announce_all_caps && !dev->ready_for_capture)
+		return -ENOTTY;
+	if (i == 0)
+		return 0;
+	return -EINVAL;
+}
+
+/* --------------- V4L2 ioctl buffer related calls ----------------- */
+
+/* negotiate buffer type
+ * only mmap streaming supported
+ * called on VIDIOC_REQBUFS
+ */
+static int vidioc_reqbufs(struct file *file, void *fh,
+			  struct v4l2_requestbuffers *b)
+{
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+	int i;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+
+	dprintk("reqbufs: %d\t%d=%d\n", b->memory, b->count,
+		dev->buffers_number);
+	if (opener->timeout_image_io) {
+		if (b->memory != V4L2_MEMORY_MMAP)
+			return -EINVAL;
+		b->count = 1;
+		return 0;
+	}
+
+	init_buffers(dev);
+	switch (b->memory) {
+	case V4L2_MEMORY_MMAP:
+		/* do nothing here, buffers are always allocated*/
+		if (b->count < 1 || dev->buffers_number < 1)
+			return 0;
+
+		if (b->count > dev->buffers_number)
+			b->count = dev->buffers_number;
+
+		/* make sure that outbufs_list contains buffers from 0 to used_buffers-1
+		 * actually, it will have been already populated via v4l2_loopback_init()
+		 * at this point */
+		if (list_empty(&dev->outbufs_list)) {
+			for (i = 0; i < dev->used_buffers; ++i)
+				list_add_tail(&dev->buffers[i].list_head,
+					      &dev->outbufs_list);
+		}
+
+		/* also, if dev->used_buffers is going to be decreased, we should remove
+		 * out-of-range buffers from outbufs_list, and fix bufpos2index mapping */
+		if (b->count < dev->used_buffers) {
+			struct v4l2l_buffer *pos, *n;
+
+			list_for_each_entry_safe (pos, n, &dev->outbufs_list,
+						  list_head) {
+				if (pos->buffer.index >= b->count)
+					list_del(&pos->list_head);
+			}
+
+			/* after we update dev->used_buffers, buffers in outbufs_list will
+			 * correspond to dev->write_position + [0;b->count-1] range */
+			i = dev->write_position;
+			list_for_each_entry (pos, &dev->outbufs_list,
+					     list_head) {
+				dev->bufpos2index[i % b->count] =
+					pos->buffer.index;
+				++i;
+			}
+		}
+
+		opener->buffers_number = b->count;
+		if (opener->buffers_number < dev->used_buffers)
+			dev->used_buffers = opener->buffers_number;
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+/* 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 *b)
+{
+	enum v4l2_buf_type type;
+	int index;
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+
+	MARK();
+
+	type = b->type;
+	index = b->index;
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+
+	if ((b->type != V4L2_BUF_TYPE_VIDEO_CAPTURE) &&
+	    (b->type != V4L2_BUF_TYPE_VIDEO_OUTPUT)) {
+		return -EINVAL;
+	}
+	if (b->index > max_buffers)
+		return -EINVAL;
+
+	if (opener->timeout_image_io)
+		*b = dev->timeout_image_buffer.buffer;
+	else
+		*b = dev->buffers[b->index % dev->used_buffers].buffer;
+
+	b->type = type;
+	b->index = index;
+	dprintkrw("buffer type: %d (of %d with size=%ld)\n", b->memory,
+		  dev->buffers_number, dev->buffer_size);
+
+	/*  Hopefully fix 'DQBUF return bad index if queue bigger then 2 for capture'
+            https://github.com/umlaeute/v4l2loopback/issues/60 */
+	b->flags &= ~V4L2_BUF_FLAG_DONE;
+	b->flags |= V4L2_BUF_FLAG_QUEUED;
+
+	return 0;
+}
+
+static void buffer_written(struct v4l2_loopback_device *dev,
+			   struct v4l2l_buffer *buf)
+{
+	del_timer_sync(&dev->sustain_timer);
+	del_timer_sync(&dev->timeout_timer);
+	spin_lock_bh(&dev->lock);
+
+	dev->bufpos2index[dev->write_position % dev->used_buffers] =
+		buf->buffer.index;
+	list_move_tail(&buf->list_head, &dev->outbufs_list);
+	++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 *private_data,
+		       struct v4l2_buffer *buf)
+{
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+	struct v4l2l_buffer *b;
+	int index;
+
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+
+	if (buf->index > max_buffers)
+		return -EINVAL;
+	if (opener->timeout_image_io)
+		return 0;
+
+	index = buf->index % dev->used_buffers;
+	b = &dev->buffers[index];
+
+	switch (buf->type) {
+	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
+		dprintkrw("capture QBUF index: %d\n", index);
+		set_queued(b);
+		return 0;
+	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
+		dprintkrw("output QBUF pos: %d index: %d\n",
+			  dev->write_position, index);
+		if (buf->timestamp.tv_sec == 0 && buf->timestamp.tv_usec == 0)
+			v4l2l_get_timestamp(&b->buffer);
+		else
+			b->buffer.timestamp = buf->timestamp;
+		b->buffer.bytesused = buf->bytesused;
+		set_done(b);
+		buffer_written(dev, b);
+
+		/*  Hopefully fix 'DQBUF return bad index if queue bigger then 2 for capture'
+                    https://github.com/umlaeute/v4l2loopback/issues/60 */
+		buf->flags &= ~V4L2_BUF_FLAG_DONE;
+		buf->flags |= V4L2_BUF_FLAG_QUEUED;
+
+		wake_up_all(&dev->read_event);
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+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 = file->private_data;
+	int pos, ret;
+	int timeout_happened;
+
+	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 = (opener->read_position + dev->used_buffers - 1) %
+		      dev->used_buffers;
+	} else {
+		opener->reread_count = 0;
+		if (dev->write_position > opener->read_position + dev->used_buffers)
+			opener->read_position = dev->write_position - 1;
+		pos = opener->read_position % dev->used_buffers;
+		++opener->read_position;
+	}
+	timeout_happened = dev->timeout_happened;
+	dev->timeout_happened = 0;
+	spin_unlock_bh(&dev->lock);
+
+	ret = dev->bufpos2index[pos];
+	if (timeout_happened) {
+		/* 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[ret].buffer.m.offset,
+		       dev->timeout_image, dev->buffer_size);
+	}
+	return ret;
+}
+
+/* put buffer to dequeue
+ * called on VIDIOC_DQBUF
+ */
+static int vidioc_dqbuf(struct file *file, void *private_data,
+			struct v4l2_buffer *buf)
+{
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+	int index;
+	struct v4l2l_buffer *b;
+
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+	if (opener->timeout_image_io) {
+		*buf = dev->timeout_image_buffer.buffer;
+		return 0;
+	}
+
+	switch (buf->type) {
+	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
+		index = get_capture_buffer(file);
+		if (index < 0)
+			return index;
+		dprintkrw("capture DQBUF pos: %d index: %d\n",
+			  opener->read_position - 1, index);
+		if (!(dev->buffers[index].buffer.flags &
+		      V4L2_BUF_FLAG_MAPPED)) {
+			dprintk("trying to return not mapped buf[%d]\n", index);
+			return -EINVAL;
+		}
+		unset_flags(&dev->buffers[index]);
+		*buf = dev->buffers[index].buffer;
+		return 0;
+	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
+		b = list_entry(dev->outbufs_list.prev, struct v4l2l_buffer,
+			       list_head);
+		list_move_tail(&b->list_head, &dev->outbufs_list);
+		dprintkrw("output DQBUF index: %d\n", b->buffer.index);
+		unset_flags(b);
+		*buf = b->buffer;
+		buf->type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+/* ------------- STREAMING ------------------- */
+
+/* start streaming
+ * called on VIDIOC_STREAMON
+ */
+static int vidioc_streamon(struct file *file, void *private_data,
+			   enum v4l2_buf_type type)
+{
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+
+	switch (type) {
+	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
+		opener->type = WRITER;
+		dev->ready_for_output = 0;
+		if (!dev->ready_for_capture) {
+			int ret = allocate_buffers(dev);
+			if (ret < 0)
+				return ret;
+			dev->ready_for_capture = 1;
+		}
+		return 0;
+	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
+		opener->type = READER;
+		if (!dev->ready_for_capture)
+			return -EIO;
+		return 0;
+	default:
+		return -EINVAL;
+	}
+	return -EINVAL;
+}
+
+/* stop streaming
+ * called on VIDIOC_STREAMOFF
+ */
+static int vidioc_streamoff(struct file *file, void *private_data,
+			    enum v4l2_buf_type type)
+{
+	struct v4l2_loopback_device *dev;
+	MARK();
+	dprintk("%d\n", type);
+
+	dev = v4l2loopback_getdevice(file);
+
+	switch (type) {
+	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
+		dev->ready_for_capture = 0;
+		return 0;
+	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
+		return 0;
+	default:
+		return -EINVAL;
+	}
+	return -EINVAL;
+}
+
+/* file operations */
+static void vm_open(struct vm_area_struct *vma)
+{
+	struct v4l2l_buffer *buf;
+	MARK();
+
+	buf = vma->vm_private_data;
+	buf->use_count++;
+}
+
+static void vm_close(struct vm_area_struct *vma)
+{
+	struct v4l2l_buffer *buf;
+	MARK();
+
+	buf = vma->vm_private_data;
+	buf->use_count--;
+}
+
+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)
+{
+	unsigned long addr;
+	unsigned long start;
+	unsigned long size;
+	struct v4l2_loopback_device *dev;
+	struct v4l2_loopback_opener *opener;
+	struct v4l2l_buffer *buffer = NULL;
+	MARK();
+
+	start = (unsigned long)vma->vm_start;
+	size = (unsigned long)(vma->vm_end - vma->vm_start);
+
+	dev = v4l2loopback_getdevice(file);
+	opener = file->private_data;
+
+	if (size > dev->buffer_size) {
+		dprintk("userspace tries to mmap too much, fail\n");
+		return -EINVAL;
+	}
+	if (opener->timeout_image_io) {
+		/* we are going to map the timeout_image_buffer */
+		if ((vma->vm_pgoff << PAGE_SHIFT) !=
+		    dev->buffer_size * MAX_BUFFERS) {
+			dprintk("invalid mmap offset for timeout_image_io mode\n");
+			return -EINVAL;
+		}
+	} else if ((vma->vm_pgoff << PAGE_SHIFT) >
+		   dev->buffer_size * (dev->buffers_number - 1)) {
+		dprintk("userspace tries to mmap too far, fail\n");
+		return -EINVAL;
+	}
+
+	/* FIXME: allocation should not happen here! */
+	if (NULL == dev->image)
+		if (allocate_buffers(dev) < 0)
+			return -EINVAL;
+
+	if (opener->timeout_image_io) {
+		buffer = &dev->timeout_image_buffer;
+		addr = (unsigned long)dev->timeout_image;
+	} else {
+		int i;
+		for (i = 0; i < dev->buffers_number; ++i) {
+			buffer = &dev->buffers[i];
+			if ((buffer->buffer.m.offset >> PAGE_SHIFT) ==
+			    vma->vm_pgoff)
+				break;
+		}
+
+		if (NULL == buffer)
+			return -EINVAL;
+
+		addr = (unsigned long)dev->image +
+		       (vma->vm_pgoff << PAGE_SHIFT);
+	}
+
+	while (size > 0) {
+		struct page *page;
+
+		page = (void *)vmalloc_to_page((void *)addr);
+
+		if (vm_insert_page(vma, start, page) < 0)
+			return -EAGAIN;
+
+		start += PAGE_SIZE;
+		addr += PAGE_SIZE;
+		size -= PAGE_SIZE;
+	}
+
+	vma->vm_ops = &vm_ops;
+	vma->vm_private_data = buffer;
+	buffer->buffer.flags |= V4L2_BUF_FLAG_MAPPED;
+
+	vm_open(vma);
+
+	MARK();
+	return 0;
+}
+
+static unsigned int v4l2_loopback_poll(struct file *file,
+				       struct poll_table_struct *pts)
+{
+	struct v4l2_loopback_opener *opener;
+	struct v4l2_loopback_device *dev;
+	int ret_mask = 0;
+	MARK();
+
+	opener = file->private_data;
+	dev = v4l2loopback_getdevice(file);
+
+	switch (opener->type) {
+	case WRITER:
+		ret_mask = POLLOUT | POLLWRNORM;
+		break;
+	case READER:
+		poll_wait(file, &dev->read_event, pts);
+		if (can_read(dev, opener))
+			ret_mask = POLLIN | POLLRDNORM;
+		break;
+	default:
+		ret_mask = -POLLERR;
+	}
+	MARK();
+
+	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;
+	MARK();
+
+	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;
+	file->private_data = opener;
+	atomic_inc(&dev->open_count);
+
+	opener->timeout_image_io = dev->timeout_image_io;
+	dev->timeout_image_io = 0;
+
+	if (opener->timeout_image_io) {
+		int r = allocate_timeout_image(dev);
+
+		if (r < 0) {
+			dprintk("timeout image allocation failed\n");
+			return r;
+		}
+	}
+	dprintk("opened dev:%p with image:%p\n", dev, dev ? dev->image : NULL);
+	MARK();
+	return 0;
+}
+
+static int v4l2_loopback_close(struct file *file)
+{
+	struct v4l2_loopback_opener *opener;
+	struct v4l2_loopback_device *dev;
+	int iswriter = 0;
+	MARK();
+
+	opener = file->private_data;
+	dev = v4l2loopback_getdevice(file);
+
+	if (WRITER == opener->type)
+		iswriter = 1;
+
+	atomic_dec(&dev->open_count);
+	if (dev->open_count.counter == 0) {
+		del_timer_sync(&dev->sustain_timer);
+		del_timer_sync(&dev->timeout_timer);
+	}
+	try_free_buffers(dev);
+	kfree(opener);
+	if (iswriter) {
+		dev->ready_for_output = 1;
+	}
+	MARK();
+	return 0;
+}
+
+static ssize_t v4l2_loopback_read(struct file *file, char __user *buf,
+				  size_t count, loff_t *ppos)
+{
+	int read_index;
+	struct v4l2_loopback_device *dev;
+	struct v4l2_buffer *b;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	read_index = get_capture_buffer(file);
+	if (read_index < 0)
+		return read_index;
+	if (count > dev->buffer_size)
+		count = dev->buffer_size;
+	b = &dev->buffers[read_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: failed copy_to_user() in read buf\n");
+		return -EFAULT;
+	}
+	dprintkrw("leave v4l2_loopback_read()\n");
+	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;
+	int write_index;
+	struct v4l2_buffer *b;
+	MARK();
+
+	dev = v4l2loopback_getdevice(file);
+
+	/* there's at least one writer, so don'stop announcing output capabilities */
+	dev->ready_for_output = 0;
+
+	if (!dev->ready_for_capture) {
+		int ret = allocate_buffers(dev);
+		if (ret < 0)
+			return ret;
+		dev->ready_for_capture = 1;
+	}
+	dprintkrw("v4l2_loopback_write() trying to write %zu bytes\n", count);
+	if (count > dev->buffer_size)
+		count = dev->buffer_size;
+
+	write_index = dev->write_position % dev->used_buffers;
+	b = &dev->buffers[write_index].buffer;
+
+	if (copy_from_user((void *)(dev->image + b->m.offset), (void *)buf,
+			   count)) {
+		printk(KERN_ERR
+		       "v4l2-loopback: failed copy_from_user() in write buf, could not write %zu\n",
+		       count);
+		return -EFAULT;
+	}
+	v4l2l_get_timestamp(b);
+	b->bytesused = count;
+	b->sequence = dev->write_position;
+	buffer_written(dev, &dev->buffers[write_index]);
+	wake_up_all(&dev->read_event);
+	dprintkrw("leave v4l2_loopback_write()\n");
+	return count;
+}
+
+/* init functions */
+/* frees buffers, if already allocated */
+static int free_buffers(struct v4l2_loopback_device *dev)
+{
+	MARK();
+	dprintk("freeing image@%p for dev:%p\n", dev ? dev->image : NULL, dev);
+	if (dev->image) {
+		vfree(dev->image);
+		dev->image = NULL;
+	}
+	if (dev->timeout_image) {
+		vfree(dev->timeout_image);
+		dev->timeout_image = NULL;
+	}
+	dev->imagesize = 0;
+
+	return 0;
+}
+/* frees buffers, if they are no longer needed */
+static void try_free_buffers(struct v4l2_loopback_device *dev)
+{
+	MARK();
+	if (0 == dev->open_count.counter && !dev->keep_format) {
+		free_buffers(dev);
+		dev->ready_for_capture = 0;
+		dev->buffer_size = 0;
+		dev->write_position = 0;
+	}
+}
+/* allocates buffers, if buffer_size is set */
+static int allocate_buffers(struct v4l2_loopback_device *dev)
+{
+	MARK();
+	/* vfree on close file operation in case no open handles left */
+	if (0 == dev->buffer_size)
+		return -EINVAL;
+
+	if (dev->image) {
+		dprintk("allocating buffers again: %ld %ld\n",
+			dev->buffer_size * dev->buffers_number, dev->imagesize);
+		/* FIXME: prevent double allocation more intelligently! */
+		if (dev->buffer_size * dev->buffers_number == dev->imagesize)
+			return 0;
+
+		/* if there is only one writer, no problem should occur */
+		if (dev->open_count.counter == 1)
+			free_buffers(dev);
+		else
+			return -EINVAL;
+	}
+
+	dev->imagesize = dev->buffer_size * dev->buffers_number;
+
+	dprintk("allocating %ld = %ldx%d\n", dev->imagesize, dev->buffer_size,
+		dev->buffers_number);
+
+	dev->image = vmalloc(dev->imagesize);
+	if (dev->timeout_jiffies > 0)
+		allocate_timeout_image(dev);
+
+	if (dev->image == NULL)
+		return -ENOMEM;
+	dprintk("vmallocated %ld bytes\n", dev->imagesize);
+	MARK();
+	init_buffers(dev);
+	return 0;
+}
+
+/* init inner buffers, they are capture mode and flags are set as
+ * for capture mod buffers */
+static void init_buffers(struct v4l2_loopback_device *dev)
+{
+	int i;
+	int buffer_size;
+	int bytesused;
+	MARK();
+
+	buffer_size = dev->buffer_size;
+	bytesused = dev->pix_format.sizeimage;
+
+	for (i = 0; i < dev->buffers_number; ++i) {
+		struct v4l2_buffer *b = &dev->buffers[i].buffer;
+		b->index = i;
+		b->bytesused = bytesused;
+		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_image_buffer = dev->buffers[0];
+	dev->timeout_image_buffer.buffer.m.offset = MAX_BUFFERS * buffer_size;
+	MARK();
+}
+
+static int allocate_timeout_image(struct v4l2_loopback_device *dev)
+{
+	MARK();
+	if (dev->buffer_size <= 0)
+		return -EINVAL;
+
+	if (dev->timeout_image == NULL) {
+		dev->timeout_image = v4l2l_vzalloc(dev->buffer_size);
+		if (dev->timeout_image == NULL)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
+/* fills and register video device */
+static void init_vdev(struct video_device *vdev, int nr)
+{
+	MARK();
+	vidioc_fill_name(vdev->name, sizeof(vdev->name), 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;
+	vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT |
+			    V4L2_CAP_READWRITE | V4L2_CAP_STREAMING;
+	vdev->device_caps |= V4L2_CAP_VIDEO_M2M;
+
+	if (debug > 1)
+		vdev->dev_debug =
+			V4L2_DEV_DEBUG_IOCTL | V4L2_DEV_DEBUG_IOCTL_ARG;
+
+	vdev->vfl_dir = VFL_DIR_M2M;
+
+	MARK();
+}
+
+/* init default capture parameters, only fps may be changed in future */
+static void init_capture_param(struct v4l2_captureparm *capture_param)
+{
+	MARK();
+	capture_param->capability = 0;
+	capture_param->capturemode = 0;
+	capture_param->extendedmode = 0;
+	capture_param->readbuffers = max_buffers;
+	capture_param->timeperframe.numerator = 1;
+	capture_param->timeperframe.denominator = 30;
+}
+
+static void check_timers(struct v4l2_loopback_device *dev)
+{
+	if (!dev->ready_for_capture)
+		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);
+}
+static void sustain_timer_clb(struct timer_list *t)
+{
+	struct v4l2_loopback_device *dev = from_timer(dev, t, sustain_timer);
+	spin_lock(&dev->lock);
+	if (dev->sustain_framerate) {
+		dev->reread_count++;
+		dprintkrw("reread: %d %d\n", 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);
+}
+static void timeout_timer_clb(struct timer_list *t)
+{
+	struct v4l2_loopback_device *dev = from_timer(dev, t, timeout_timer);
+	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 */
+static int v4l2_loopback_init(struct v4l2_loopback_device *dev, int nr)
+{
+	int ret;
+	struct v4l2_ctrl_handler *hdl = &dev->ctrl_handler;
+	snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
+		 "v4l2loopback-%03d", nr);
+	ret = v4l2_device_register(NULL, &dev->v4l2_dev);
+	if (ret)
+		return ret;
+
+	MARK();
+	dev->vdev = video_device_alloc();
+	if (dev->vdev == NULL) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	video_set_drvdata(dev->vdev,
+			  kzalloc(sizeof(struct v4l2loopback_private),
+				  GFP_KERNEL));
+	if (video_get_drvdata(dev->vdev) == NULL) {
+		ret = -ENOMEM;
+		goto error;
+	}
+	((struct v4l2loopback_private *)video_get_drvdata(dev->vdev))->devicenr =
+		nr;
+
+	init_vdev(dev->vdev, nr);
+	dev->vdev->v4l2_dev = &dev->v4l2_dev;
+	init_capture_param(&dev->capture_param);
+	set_timeperframe(dev, &dev->capture_param.timeperframe);
+	dev->keep_format = 0;
+	dev->sustain_framerate = 0;
+	dev->buffers_number = max_buffers;
+	dev->used_buffers = max_buffers;
+	dev->max_openers = max_openers;
+	dev->write_position = 0;
+	spin_lock_init(&dev->lock);
+	INIT_LIST_HEAD(&dev->outbufs_list);
+	if (list_empty(&dev->outbufs_list)) {
+		int i;
+
+		for (i = 0; i < dev->used_buffers; ++i)
+			list_add_tail(&dev->buffers[i].list_head,
+				      &dev->outbufs_list);
+	}
+	memset(dev->bufpos2index, 0, sizeof(dev->bufpos2index));
+	atomic_set(&dev->open_count, 0);
+	dev->ready_for_capture = 0;
+	dev->ready_for_output = 1;
+	dev->announce_all_caps = (!exclusive_caps[nr]);
+
+	dev->buffer_size = 0;
+	dev->image = NULL;
+	dev->imagesize = 0;
+	timer_setup(&dev->sustain_timer, sustain_timer_clb, 0);
+	timer_setup(&dev->timeout_timer, timeout_timer_clb, 0);
+	dev->reread_count = 0;
+	dev->timeout_jiffies = 0;
+	dev->timeout_image = NULL;
+	dev->timeout_happened = 0;
+
+	ret = v4l2_ctrl_handler_init(hdl, 1);
+	if (ret)
+		goto error;
+	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) {
+		ret = hdl->error;
+		goto error;
+	}
+	dev->v4l2_dev.ctrl_handler = hdl;
+
+	/* FIXME set buffers to 0 */
+
+	/* Set initial format */
+	dev->pix_format.width = 0; /* V4L2LOOPBACK_SIZE_DEFAULT_WIDTH; */
+	dev->pix_format.height = 0; /* V4L2LOOPBACK_SIZE_DEFAULT_HEIGHT; */
+	dev->pix_format.pixelformat = formats[0].fourcc;
+	dev->pix_format.colorspace =
+		V4L2_COLORSPACE_SRGB; /* do we need to set this ? */
+	dev->pix_format.field = V4L2_FIELD_NONE;
+
+	dev->buffer_size = PAGE_ALIGN(dev->pix_format.sizeimage);
+	dprintk("buffer_size = %ld (=%d)\n", dev->buffer_size,
+		dev->pix_format.sizeimage);
+	allocate_buffers(dev);
+
+	init_waitqueue_head(&dev->read_event);
+
+	MARK();
+	return 0;
+
+error:
+	v4l2_ctrl_handler_free(&dev->ctrl_handler);
+	v4l2_device_unregister(&dev->v4l2_dev);
+	kfree(dev->vdev);
+	return ret;
+};
+
+/* LINUX KERNEL */
+static const struct v4l2_file_operations v4l2_loopback_fops = {
+	.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,
+};
+
+static const struct v4l2_ioctl_ops v4l2_loopback_ioctl_ops = {
+	.vidioc_querycap = &vidioc_querycap,
+	.vidioc_enum_framesizes = &vidioc_enum_framesizes,
+	.vidioc_enum_frameintervals = &vidioc_enum_frameintervals,
+
+	.vidioc_queryctrl = &vidioc_queryctrl,
+	.vidioc_g_ctrl = &vidioc_g_ctrl,
+	.vidioc_s_ctrl = &vidioc_s_ctrl,
+
+	.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,
+};
+
+static void zero_devices(void)
+{
+	int i;
+
+	MARK();
+	for (i = 0; i < MAX_DEVICES; i++)
+		devs[i] = NULL;
+}
+
+static void free_devices(void)
+{
+	int i;
+
+	MARK();
+	for (i = 0; i < devices; i++) {
+		if (NULL != devs[i]) {
+			free_buffers(devs[i]);
+			v4l2loopback_remove_sysfs(devs[i]->vdev);
+			kfree(video_get_drvdata(devs[i]->vdev));
+			video_unregister_device(devs[i]->vdev);
+			v4l2_device_unregister(&devs[i]->v4l2_dev);
+			v4l2_ctrl_handler_free(&devs[i]->ctrl_handler);
+			kfree(devs[i]);
+			devs[i] = NULL;
+		}
+	}
+}
+
+static int __init v4l2loopback_init_module(void)
+{
+	int i;
+	MARK();
+
+	zero_devices();
+	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
+		       "v4l2loopback: number of devices is limited to: %d\n",
+		       MAX_DEVICES);
+	}
+
+	if (max_buffers > MAX_BUFFERS) {
+		max_buffers = MAX_BUFFERS;
+		printk(KERN_INFO
+		       "v4l2loopback: number of buffers is limited to: %d\n",
+		       MAX_BUFFERS);
+	}
+
+	if (max_openers < 0) {
+		printk(KERN_INFO
+		       "v4l2loopback: allowing %d openers rather than %d\n",
+		       2, max_openers);
+		max_openers = 2;
+	}
+
+	if (max_width < 1) {
+		max_width = V4L2LOOPBACK_SIZE_DEFAULT_MAX_WIDTH;
+		printk(KERN_INFO "v4l2loopback: using max_width %d\n",
+		       max_width);
+	}
+	if (max_height < 1) {
+		max_height = V4L2LOOPBACK_SIZE_DEFAULT_MAX_HEIGHT;
+		printk(KERN_INFO "v4l2loopback: using max_height %d\n",
+		       max_height);
+	}
+
+	/* kfree on module release */
+	for (i = 0; i < devices; i++) {
+		int ret;
+		dprintk("creating v4l2loopback-device #%d\n", i);
+		devs[i] = kzalloc(sizeof(*devs[i]), GFP_KERNEL);
+		if (devs[i] == NULL) {
+			free_devices();
+			return -ENOMEM;
+		}
+		ret = v4l2_loopback_init(devs[i], i);
+		if (ret < 0) {
+			free_devices();
+			return ret;
+		}
+		/* register the device -> it creates /dev/video* */
+		if (video_register_device(devs[i]->vdev, VFL_TYPE_VIDEO,
+					  video_nr[i]) < 0) {
+			video_device_release(devs[i]->vdev);
+			printk(KERN_ERR
+			       "v4l2loopback: failed video_register_device()\n");
+			free_devices();
+			return -EFAULT;
+		}
+		v4l2loopback_create_sysfs(devs[i]->vdev);
+	}
+
+	dprintk("module installed\n");
+
+	printk(KERN_INFO "v4l2loopback driver version %d.%d.%d loaded\n",
+	       (V4L2LOOPBACK_VERSION_CODE >> 16) & 0xff,
+	       (V4L2LOOPBACK_VERSION_CODE >> 8) & 0xff,
+	       (V4L2LOOPBACK_VERSION_CODE)&0xff);
+
+	return 0;
+}
+
+static void v4l2loopback_cleanup_module(void)
+{
+	MARK();
+	/* unregister the device -> it deletes /dev/video* */
+	free_devices();
+	dprintk("module removed\n");
+}
+
+#ifdef MODULE
+int __init init_module(void)
+{
+	return v4l2loopback_init_module();
+}
+void __exit cleanup_module(void)
+{
+	return v4l2loopback_cleanup_module();
+}
+#else
+late_initcall(v4l2loopback_init_module);
+#endif