Hello, please review new version of v4l2 loopback driver.
driver works fine but there are things which I am not shure in.
Is it ok not to count mmaped buffers and just free memory when no open
file descriptors left?

Here is patch against current v4l-dvb tree
-----
This patch introduces v4l2 loopback module

From: Vasily Levin <vas...@gmail.com>

This is v4l2 loopback driver which can be used to make available any userspace
video as v4l2 device. Initialy it was written to make videoeffects available
to Skype, but in fact it have many more uses.

Priority: normal

Signed-off-by: Vasily Levin <vas...@gmail.com>

diff -uprN v4l-dvb.orig/linux/drivers/media/video/Kconfig
v4l-dvb.my/linux/drivers/media/video/Kconfig
--- v4l-dvb.orig/linux/drivers/media/video/Kconfig      2009-03-21
07:08:06.000000000 +0200
+++ v4l-dvb.my/linux/drivers/media/video/Kconfig        2009-03-24
12:58:38.000000000 +0200
@@ -465,6 +465,13 @@ config VIDEO_VIVI
          Say Y here if you want to test video apps or debug V4L devices.
          In doubt, say N.

+config VIDEO_V4L2_LOOPBACK
+       tristate "v4l2 loopback driver"
+       depends on VIDEO_V4L2 && VIDEO_DEV
+       help
+         Say Y if you want to use v4l2 loopback driver.
+         This driver can be compiled as a module, called v4l2loopback.
+
 source "drivers/media/video/bt8xx/Kconfig"

 config VIDEO_SAA6588
@@ -899,7 +906,7 @@ config USB_S2255
        depends on VIDEO_V4L2
        select VIDEOBUF_VMALLOC
        default n
-       help
+       ---help---
          Say Y here if you want support for the Sensoray 2255 USB device.
          This driver can be compiled as a module, called s2255drv.

diff -uprN v4l-dvb.orig/linux/drivers/media/video/Makefile
v4l-dvb.my/linux/drivers/media/video/Makefile
--- v4l-dvb.orig/linux/drivers/media/video/Makefile     2009-03-21
07:08:06.000000000 +0200
+++ v4l-dvb.my/linux/drivers/media/video/Makefile       2009-03-24
12:54:59.000000000 +0200
@@ -132,6 +132,7 @@ obj-$(CONFIG_VIDEO_IVTV) += ivtv/
 obj-$(CONFIG_VIDEO_CX18) += cx18/

 obj-$(CONFIG_VIDEO_VIVI) += vivi.o
+obj-$(CONFIG_VIDEO_V4L2_LOOPBACK) += v4l2loopback.o
 obj-$(CONFIG_VIDEO_CX23885) += cx23885/

 obj-$(CONFIG_VIDEO_MX3)                        += mx3_camera.o
diff -uprN v4l-dvb.orig/linux/drivers/media/video/v4l2loopback.c
v4l-dvb.my/linux/drivers/media/video/v4l2loopback.c
--- v4l-dvb.orig/linux/drivers/media/video/v4l2loopback.c       1970-01-01
03:00:00.000000000 +0300
+++ v4l-dvb.my/linux/drivers/media/video/v4l2loopback.c 2009-03-24
18:51:41.000000000 +0200
@@ -0,0 +1,726 @@
+/*
+ *      v4l2loopback.c  --  video 4 linux loopback driver
+ *
+ *      Copyright (C) 2005-2009
+ *          Vasily Levin (vas...@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 <media/v4l2-ioctl.h>
+#include "v4l2loopback.h"
+
+#define DEBUG
+#define DEBUG_RW
+#define YAVLD_STREAMING
+#define KERNEL_PREFIX "YAVLD device: " /* Prefix of each kernel message */
+/* global module data */
+struct v4l2_loopback_device *dev;
+/* forward declarations */
+static void init_buffers(int buffer_size);
+static const struct v4l2_file_operations v4l2_loopback_fops;
+static const struct v4l2_ioctl_ops v4l2_loopback_ioctl_ops;
+/****************************************************************
+**************** my queue helpers *******************************
+****************************************************************/
+/* next functions sets buffer flags and adjusts counters accordingly */
+void set_done(struct v4l2_buffer *buffer)
+{
+       buffer->flags |= V4L2_BUF_FLAG_DONE;
+       buffer->flags &= ~V4L2_BUF_FLAG_QUEUED;
+}
+
+void set_queued(struct v4l2_buffer *buffer)
+{
+       buffer->flags |= V4L2_BUF_FLAG_QUEUED;
+       buffer->flags &= ~V4L2_BUF_FLAG_DONE;
+}
+
+void unset_all(struct v4l2_buffer *buffer)
+{
+       buffer->flags &= ~V4L2_BUF_FLAG_QUEUED;
+       buffer->flags &= ~V4L2_BUF_FLAG_DONE;
+}
+/****************************************************************
+**************** V4L2 ioctl caps and params calls ***************
+****************************************************************/
+/******************************************************************************/
+/* returns device capabilities, called on VIDIOC_QUERYCAP ioctl*/
+static int vidioc_querycap(struct file *file,
+                          void *priv, struct v4l2_capability *cap)
+{
+       strcpy(cap->driver, "v4l2 loopback");
+       strcpy(cap->card, "Dummy video device");
+       cap->version = 1;
+       cap->capabilities =
+           V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_VIDEO_OUTPUT |
+           V4L2_CAP_READWRITE
+#ifdef YAVLD_STREAMING
+           | V4L2_CAP_STREAMING
+#endif
+           ;
+       return 0;
+}
+
+/******************************************************************************/
+/* returns device formats, called on VIDIOC_ENUM_FMT ioctl*/
+static int vidioc_enum_fmt_cap(struct file *file, void *fh,
+                              struct v4l2_fmtdesc *f)
+{
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       if (f->index)
+               return -EINVAL;
+       strcpy(f->description, "current format");
+       f->pixelformat = dev->pix_format.pixelformat;
+       return 0;
+};
+
+/******************************************************************************/
+/* returns current video format format fmt, called on VIDIOC_G_FMT ioctl */
+static int vidioc_g_fmt_cap(struct file *file,
+                           void *priv, struct v4l2_format *fmt)
+{
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       fmt->fmt.pix = dev->pix_format;
+       return 0;
+}
+
+/******************************************************************************/
+/* checks if it is OK to change to format fmt, called on VIDIOC_TRY_FMT ioctl
+ * with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE */
+/* actual check is done by inner_try_fmt_cap */
+/* just checking that pixelformat is OK and set other parameters, app should
+ * obey this decidion */
+static int vidioc_try_fmt_cap(struct file *file,
+                             void *priv, struct v4l2_format *fmt)
+{
+       struct v4l2_loopback_opener *opener = file->private_data;
+       opener->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       if (fmt->fmt.pix.pixelformat != dev->pix_format.pixelformat)
+               return -EINVAL;
+       fmt->fmt.pix = dev->pix_format;
+       return 0;
+}
+
+/******************************************************************************/
+/* checks if it is OK to change to format fmt, called on VIDIOC_TRY_FMT ioctl
+ * with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT */
+/* if format is negotiated do not change it */
+static int vidioc_try_fmt_video_output(struct file *file,
+                                      void *priv, struct v4l2_format *fmt)
+{
+       struct v4l2_loopback_opener *opener = file->private_data;
+       opener->type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
+       /* 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 {
+               if (fmt->fmt.pix.sizeimage == 0)
+                       return -1;
+               dev->pix_format = fmt->fmt.pix;
+       }
+       return 0;
+};
+
+/******************************************************************************/
+/* sets new output format, if possible, called on VIDIOC_S_FMT ioctl
+ * with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_CAPTURE */
+/* 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) */
+static int vidioc_s_fmt_cap(struct file *file,
+                           void *priv, struct v4l2_format *fmt)
+{
+       return vidioc_try_fmt_cap(file, priv, fmt);
+}
+
+/******************************************************************************/
+/* sets new output format, if possible, called on VIDIOC_S_FMT ioctl
+ * with v4l2_buf_type set to V4L2_BUF_TYPE_VIDEO_OUTPUT */
+/* allocate data here because we do not know if it will be streaming or
+ * read/write IO */
+static int vidioc_s_fmt_video_output(struct file *file,
+                                    void *priv, struct v4l2_format *fmt)
+{
+       vidioc_try_fmt_video_output(file, priv, fmt);
+       if (dev->ready_for_capture == 0) {
+               dev->buffer_size = PAGE_ALIGN(dev->pix_format.sizeimage);
+               fmt->fmt.pix.sizeimage = dev->buffer_size;
+               /* vfree on close file operation in case no open handles left */
+               dev->image =
+                   vmalloc(dev->buffer_size * dev->buffers_number);
+               if (dev->image == NULL)
+                       return -EINVAL;
+#ifdef DEBUG
+               printk(KERNEL_PREFIX "vmallocated %ld bytes\n",
+                      dev->buffer_size * dev->buffers_number);
+#endif
+               init_buffers(dev->buffer_size);
+               dev->ready_for_capture = 1;
+       }
+       return 0;
+}
+
+/******************************************************************************/
+/*get some data flaw 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 */
+       parm->parm.capture = dev->capture_param;
+       return 0;
+}
+
+/******************************************************************************/
+/*get some data flaw 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)
+{
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "vidioc_s_parm called frate=%d/%d\n",
+              parm->parm.capture.timeperframe.numerator,
+              parm->parm.capture.timeperframe.denominator);
+#endif
+       switch (parm->type) {
+       case V4L2_BUF_TYPE_VIDEO_CAPTURE:{
+                       parm->parm.capture = dev->capture_param;
+                       return 0;
+               }
+       case V4L2_BUF_TYPE_VIDEO_OUTPUT:{
+                       /* TODO(vasaka) do nothing now, but should set fps if
+                        * needed */
+                       parm->parm.capture = dev->capture_param;
+                       return 0;
+               }
+       default:{
+                       return -1;
+               }
+       }
+}
+
+/* sets a tv standart, actually we do not need to handle this any spetial way
+ *added to support effecttv */
+static int vidioc_s_std(struct file *file, void *private_data,
+                       v4l2_std_id *norm)
+{
+       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)
+{
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       if (inp->index == 0) {
+               strcpy(inp->name, "loopback");
+               inp->type = V4L2_INPUT_TYPE_CAMERA;
+               inp->audioset = 0;
+               inp->tuner = 0;
+               inp->std = V4L2_STD_PAL_B;
+               inp->status = 0;
+               return 0;
+       }
+       return -EINVAL;
+}
+
+/* which input is currently active, called on VIDIOC_G_INPUT */
+int vidioc_g_input(struct file *file, void *fh, unsigned int *i)
+{
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       *i = 0;
+       return 0;
+}
+
+/* set input, can make sense if we have more than one video src,
+ * called on VIDIOC_S_INPUT */
+int vidioc_s_input(struct file *file, void *fh, unsigned int i)
+{
+       if (dev->ready_for_capture == 0)
+               return -EINVAL;
+       if (i == 0)
+               return 0;
+       return -EINVAL;
+}
+
+/***************************************************************
+**************** V4L2 ioctl buffer related calls ***************
+***************************************************************/
+/* negotiate buffer type, called on VIDIOC_REQBUFS */
+/* only mmap streaming supported */
+static int vidioc_reqbufs(struct file *file, void *fh,
+                         struct v4l2_requestbuffers *b)
+{
+       switch (b->memory) {
+       case V4L2_MEMORY_MMAP:{
+                       /* do nothing here, buffers are always allocated*/
+                       if (b->count == 0)
+                               return 0;
+                       b->count = dev->buffers_number;
+                       return 0;
+               }
+       default:{
+                       return -EINVAL;
+               }
+       }
+}
+
+/* returns buffer asked for, called on VIDIOC_QUERYBUF */
+/* give app as many buffers as it wants, if it less than 100 :-),
+ * but map them in our inner buffers */
+static int vidioc_querybuf(struct file *file, void *fh,
+                          struct v4l2_buffer *b)
+{
+       enum v4l2_buf_type type = b->type;
+       int index = b->index;
+       if ((b->type != V4L2_BUF_TYPE_VIDEO_CAPTURE) &&
+           (b->type != V4L2_BUF_TYPE_VIDEO_OUTPUT)) {
+               return -EINVAL;
+       }
+       if (b->index > 100)
+               return -EINVAL;
+       *b = dev->buffers[b->index % dev->buffers_number];
+       b->type = type;
+       b->index = index;
+       return 0;
+}
+
+/* put buffer to queue, called on VIDIOC_QBUF */
+static int vidioc_qbuf(struct file *file, void *private_data,
+                      struct v4l2_buffer *buf)
+{
+       int index = buf->index % dev->buffers_number;
+       if (buf->index > 100)
+               return -EINVAL;
+       switch (buf->type) {
+       case V4L2_BUF_TYPE_VIDEO_CAPTURE:{
+                       set_queued(&dev->buffers[index]);
+                       return 0;
+               }
+       case V4L2_BUF_TYPE_VIDEO_OUTPUT:{
+                       do_gettimeofday(&dev->buffers[index].timestamp);
+                       set_done(&dev->buffers[index]);
+                       wake_up_all(&dev->read_event);
+                       return 0;
+               }
+       default:{
+                       return -EINVAL;
+               }
+       }
+}
+
+/* put buffer to dequeue, called on VIDIOC_DQBUF */
+static int vidioc_dqbuf(struct file *file, void *private_data,
+                       struct v4l2_buffer *buf)
+{
+       int index;
+       struct v4l2_loopback_opener *opener = file->private_data;
+       switch (buf->type) {
+       case V4L2_BUF_TYPE_VIDEO_CAPTURE:{
+                       if ((dev->write_position <= opener->position) &&
+                               (file->f_flags&O_NONBLOCK))
+                               return -EAGAIN;
+                       wait_event_interruptible(dev->read_event,
+                                                (dev->write_position >
+                                                opener->position));
+                       if (dev->write_position > opener->position+2)
+                               opener->position = dev->write_position - 1;
+                       index = opener->position % dev->buffers_number;
+                       if (!(dev->buffers[index].flags&V4L2_BUF_FLAG_MAPPED)) {
+                               printk(KERN_INFO
+                                      "trying to g\return not mapped buf\n");
+                               return -EINVAL;
+                       }
+                       ++opener->position;
+                       unset_all(&dev->buffers[index]);
+                       *buf = dev->buffers[index];
+                       return 0;
+               }
+       case V4L2_BUF_TYPE_VIDEO_OUTPUT:{
+                       index = dev->write_position % dev->buffers_number;
+                       unset_all(&dev->buffers[index]);
+                       *buf = dev->buffers[index];
+                       ++dev->write_position;
+                       return 0;
+               }
+       default:{
+                       return -EINVAL;
+               }
+       }
+}
+
+static int vidioc_streamon(struct file *file, void *private_data,
+                          enum v4l2_buf_type type)
+{
+       return 0;
+}
+
+static int vidioc_streamoff(struct file *file, void *private_data,
+                           enum v4l2_buf_type type)
+{
+       return 0;
+}
+
+#ifdef CONFIG_VIDEO_V4L1_COMPAT
+int vidiocgmbuf(struct file *file, void *fh, struct video_mbuf *p)
+{
+       p->frames = dev->buffers_number;
+       p->offsets[0] = 0;
+       p->offsets[1] = 0;
+       p->size = dev->buffer_size;
+       return 0;
+}
+#endif
+/************************************************
+**************** file operations  ***************
+************************************************/
+static void vm_open(struct vm_area_struct *vma)
+{
+       /* TODO(vasaka) do open counter here */
+}
+
+static void vm_close(struct vm_area_struct *vma)
+{
+       /* TODO(vasaka) do open counter here */
+}
+
+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)
+{
+
+       struct page *page = NULL;
+
+       unsigned long addr;
+       unsigned long start = (unsigned long) vma->vm_start;
+       unsigned long size = (unsigned long) (vma->vm_end - vma->vm_start);
+
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "entering v4l_mmap(), offset: %lu\n",
+              vma->vm_pgoff);
+#endif
+       if (size > dev->buffer_size) {
+               printk(KERNEL_PREFIX
+                      "userspace tries to mmap to much, fail\n");
+               return -EINVAL;
+       }
+       if ((vma->vm_pgoff << PAGE_SHIFT) >
+           dev->buffer_size * (dev->buffers_number - 1)) {
+               printk(KERNEL_PREFIX
+                      "userspace tries to mmap to far, fail\n");
+               return -EINVAL;
+       }
+       addr = (unsigned long) dev->image + (vma->vm_pgoff << PAGE_SHIFT);
+
+       while (size > 0) {
+               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 = 0;
+       dev->buffers[(vma->vm_pgoff<<PAGE_SHIFT)/dev->buffer_size].flags |=
+               V4L2_BUF_FLAG_MAPPED;
+
+       vm_open(vma);
+
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "leaving v4l_mmap()\n");
+#endif
+
+       return 0;
+}
+
+static unsigned int v4l2_loopback_poll(struct file *file,
+                                      struct poll_table_struct *pts)
+{
+       struct v4l2_loopback_opener *opener = file->private_data;
+       int ret_mask = 0;
+       switch (opener->type) {
+               case WRITER: {
+                       ret_mask = POLLOUT | POLLWRNORM;
+               }
+               case READER: {
+                       poll_wait(file, &dev->read_event, pts);
+                       if (dev->write_position > opener->position)
+                               ret_mask =  POLLIN | POLLRDNORM;
+               }
+               default: {
+                       ret_mask = -POLLERR;
+               }
+       }
+       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 v4l_loopback_open(struct file *file)
+{
+       struct v4l2_loopback_opener *opener;
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "entering v4l_open()\n");
+#endif
+       if (dev->open_count == V4L2_LOOPBACK_MAX_OPENERS)
+               return -EBUSY;
+       /* kfree on close */
+       opener = kzalloc(sizeof(*opener), GFP_KERNEL);
+       if (opener == NULL)
+               return -ENOMEM;
+       file->private_data = opener;
+       ++dev->open_count;
+       return 0;
+}
+
+static int v4l_loopback_close(struct file *file)
+{
+       struct v4l2_loopback_opener *opener = file->private_data;
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "entering v4l_close()\n");
+#endif
+       --dev->open_count;
+       /* TODO(vasaka) does the closed file means that mmaped buffers are
+        * no more valid and one can free data? */
+       if (dev->open_count == 0) {
+               vfree(dev->image);
+               dev->image = NULL;
+               dev->ready_for_capture = 0;
+       }
+       kfree(opener);
+       return 0;
+}
+
+static ssize_t v4l_loopback_read(struct file *file, char __user *buf,
+                                size_t count, loff_t *ppos)
+{
+       int read_index;
+       struct v4l2_loopback_opener *opener = file->private_data;
+       if ((dev->write_position <= opener->position) &&
+               (file->f_flags&O_NONBLOCK)) {
+               return -EAGAIN;
+       }
+       wait_event_interruptible(dev->read_event,
+                                (dev->write_position > opener->position));
+       if (count > dev->buffer_size)
+               count = dev->buffer_size;
+       if (dev->write_position > opener->position+2)
+               opener->position = dev->write_position - 1;
+       read_index = opener->position % dev->buffers_number;
+       if (copy_to_user((void *) buf, (void *) (dev->image +
+                        dev->buffers[read_index].m.offset), count)) {
+               printk(KERN_INFO "failed copy_from_user() in write buf\n");
+               return -EFAULT;
+       }
+       ++opener->position;
+#ifdef DEBUG_RW
+       printk(KERNEL_PREFIX "leave v4l2_loopback_read()\n");
+#endif
+       return count;
+}
+
+static ssize_t v4l_loopback_write(struct file *file,
+                                 const char __user *buf, size_t count,
+                                 loff_t *ppos)
+{
+       int write_index = dev->write_position % dev->buffers_number;
+#ifdef DEBUG_RW
+       printk(KERNEL_PREFIX
+              "v4l2_loopback_write() trying to write %d bytes\n", count);
+#endif
+       if (count > dev->buffer_size)
+               count = dev->buffer_size;
+       if (copy_from_user(
+                  (void *) (dev->image + dev->buffers[write_index].m.offset),
+                  (void *) buf, count)) {
+               printk(KERNEL_PREFIX
+                  "failed copy_from_user() in write buf, could not write %d\n",
+                  count);
+               return -EFAULT;
+       }
+       do_gettimeofday(&dev->buffers[write_index].timestamp);
+       dev->buffers[write_index].sequence = dev->write_position++;
+       wake_up_all(&dev->read_event);
+#ifdef DEBUG_RW
+       printk(KERNEL_PREFIX "leave v4l2_loopback_write()\n");
+#endif
+       return count;
+}
+
+/************************************************
+**************** init functions *****************
+************************************************/
+/* init inner buffers, they are capture mode and flags are set as
+ * for capture mod buffers */
+static void init_buffers(int buffer_size)
+{
+       int i;
+       for (i = 0; i < dev->buffers_number; ++i) {
+               dev->buffers[i].bytesused = buffer_size;
+               dev->buffers[i].length = buffer_size;
+               dev->buffers[i].field = V4L2_FIELD_NONE;
+               dev->buffers[i].flags = 0;
+               dev->buffers[i].index = i;
+               dev->buffers[i].input = 0;
+               dev->buffers[i].m.offset = i * buffer_size;
+               dev->buffers[i].memory = V4L2_MEMORY_MMAP;
+               dev->buffers[i].sequence = 0;
+               dev->buffers[i].timestamp.tv_sec = 0;
+               dev->buffers[i].timestamp.tv_usec = 0;
+               dev->buffers[i].type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+       }
+       dev->write_position = 0;
+}
+
+/* fills and register video device */
+static void init_vdev(struct video_device *vdev)
+{
+       strcpy(vdev->name, "Dummy video device");
+       vdev->tvnorms = V4L2_STD_NTSC | V4L2_STD_SECAM | V4L2_STD_PAL;/* TODO */
+       vdev->current_norm = V4L2_STD_PAL_B, /* do not know what is best here */
+       vdev->vfl_type = VFL_TYPE_GRABBER;
+       vdev->fops = &v4l2_loopback_fops;
+       vdev->ioctl_ops = &v4l2_loopback_ioctl_ops;
+       vdev->release = &video_device_release;
+       vdev->minor = -1;
+#ifdef DEBUG
+       vdev->debug = V4L2_DEBUG_IOCTL | V4L2_DEBUG_IOCTL_ARG;
+#endif
+}
+
+/* init default capture paramete, only fps may be changed in future */
+static void init_capture_param(struct v4l2_captureparm *capture_param)
+{
+       capture_param->capability = 0;
+       capture_param->capturemode = 0;
+       capture_param->extendedmode = 0;
+       capture_param->readbuffers = V4L2_LOOPBACK_BUFFERS_NUMBER;
+       capture_param->timeperframe.numerator = 1;
+       capture_param->timeperframe.denominator = 30;
+}
+
+/* init loopback main structure */
+static int v4l2_loopback_init(struct v4l2_loopback_device *dev)
+{
+       dev->vdev = video_device_alloc();
+       if (dev->vdev == NULL)
+               return -1;
+       init_vdev(dev->vdev);
+       init_capture_param(&dev->capture_param);
+       dev->buffers_number = V4L2_LOOPBACK_BUFFERS_NUMBER;
+       dev->open_count = 0;
+       dev->ready_for_capture = 0;
+       dev->buffer_size = 0;
+       dev->image = NULL;
+       /* kfree on module release */
+       dev->buffers =
+           kzalloc(sizeof(*dev->buffers) * dev->buffers_number,
+                   GFP_KERNEL);
+       if (dev->buffers == NULL)
+               return -ENOMEM;
+       init_waitqueue_head(&dev->read_event);
+       return 0;
+};
+
+/***********************************************
+**************** LINUX KERNEL ****************
+************************************************/
+static const struct v4l2_file_operations v4l2_loopback_fops = {
+      .owner = THIS_MODULE,
+      .open = v4l_loopback_open,
+      .release = v4l_loopback_close,
+      .read = v4l_loopback_read,
+      .write = v4l_loopback_write,
+      .poll = v4l2_loopback_poll,
+      .mmap = v4l2_loopback_mmap,
+      .ioctl = video_ioctl2,
+};
+
+static const struct v4l2_ioctl_ops v4l2_loopback_ioctl_ops = {
+       .vidioc_querycap = &vidioc_querycap,
+       .vidioc_enum_fmt_vid_cap = &vidioc_enum_fmt_cap,
+       .vidioc_enum_input = &vidioc_enum_input,
+       .vidioc_g_input = &vidioc_g_input,
+       .vidioc_s_input = &vidioc_s_input,
+       .vidioc_g_fmt_vid_cap = &vidioc_g_fmt_cap,
+       .vidioc_s_fmt_vid_cap = &vidioc_s_fmt_cap,
+       .vidioc_s_fmt_vid_out = &vidioc_s_fmt_video_output,
+       .vidioc_try_fmt_vid_cap = &vidioc_try_fmt_cap,
+       .vidioc_try_fmt_vid_out = &vidioc_try_fmt_video_output,
+       .vidioc_s_std = &vidioc_s_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
+};
+
+int __init init_module()
+{
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "entering init_module()\n");
+#endif
+       /* kfree on module release */
+       dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+       if (dev == NULL)
+               return -ENOMEM;
+       if (v4l2_loopback_init(dev) < 0)
+               return -EINVAL;
+       /* register the device -> it creates /dev/video* */
+       if (video_register_device(dev->vdev, VFL_TYPE_GRABBER, -1) < 0) {
+               video_device_release(dev->vdev);
+               printk(KERN_INFO "failed video_register_device()\n");
+               return -EINVAL;
+       }
+       printk(KERNEL_PREFIX "module installed\n");
+       return 0;
+}
+
+void __exit cleanup_module()
+{
+#ifdef DEBUG
+       printk(KERNEL_PREFIX "entering cleanup_module()\n");
+#endif
+       /* unregister the device -> it deletes /dev/video* */
+       video_unregister_device(dev->vdev);
+       kfree(dev->buffers);
+       kfree(dev);
+       printk(KERNEL_PREFIX "module removed\n");
+}
+
+
+MODULE_DESCRIPTION("YAVLD - V4L2 loopback video device");
+MODULE_VERSION("0.0.1");
+MODULE_AUTHOR("Vasily Levin");
+MODULE_LICENSE("GPL");
diff -uprN v4l-dvb.orig/linux/drivers/media/video/v4l2loopback.h
v4l-dvb.my/linux/drivers/media/video/v4l2loopback.h
--- v4l-dvb.orig/linux/drivers/media/video/v4l2loopback.h       1970-01-01
03:00:00.000000000 +0300
+++ v4l-dvb.my/linux/drivers/media/video/v4l2loopback.h 2009-03-24
18:21:58.000000000 +0200
@@ -0,0 +1,58 @@
+/*
+ *      v4l2loopback.h  --  video 4 linux loopback driver
+ *
+ *      Copyright (C) 2005-2009
+ *          Vasily Levin (vas...@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.
+ *
+ */
+
+#ifndef _V4L2LOOPBACK_H
+#define        _V4L2LOOPBACK_H
+
+#include <linux/videodev2.h>
+#include <media/v4l2-common.h>
+ /* fixed inner buffers number */
+/* TODO(vasaka) make this module parameter */
+#define V4L2_LOOPBACK_BUFFERS_NUMBER 4
+#define V4L2_LOOPBACK_MAX_OPENERS 10
+
+/* 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 v4l2_loopback_device {
+       struct video_device *vdev;
+       /* pixel and stream format */
+       struct v4l2_pix_format pix_format;
+       struct v4l2_captureparm capture_param;
+       /* buffers stuff */
+       __u8 *image;         /* pointer to actual buffers data */
+       int buffers_number;  /* should not be big, 4 is a good choise */
+       struct v4l2_buffer *buffers;    /* inner driver buffers */
+       int write_position; /* number of last written frame + 1 */
+       long buffer_size;
+       /* sync stuff */
+       int open_count;
+       int ready_for_capture;/* set to true when at least one writer opened
+                             * device and negotiated format */
+       wait_queue_head_t read_event;
+};
+/* 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 buffers_number;
+       int position; /* number of last processed frame + 1 or
+                      * write_position - 1 if reader went out of sinc */
+       struct v4l2_buffer *buffers;
+};
+#endif                         /* _V4L2LOOPBACK_H */
diff -uprN v4l-dvb.orig/v4l/.config v4l-dvb.my/v4l/.config
--- v4l-dvb.orig/v4l/.config    2009-03-24 03:45:35.000000000 +0200
+++ v4l-dvb.my/v4l/.config      2009-03-24 12:58:09.000000000 +0200
@@ -37,6 +37,7 @@ CONFIG_DVB_B2C2_FLEXCOP_PCI=m
 CONFIG_RADIO_AZTECH=m
 CONFIG_VIDEO_BT848=m
 CONFIG_VIDEO_VIVI=m
+CONFIG_VIDEO_V4L2_LOOPBACK=m
 CONFIG_DVB_USB_CXUSB=m
 CONFIG_USB_GSPCA_FINEPIX=m
 CONFIG_SOC_CAMERA_MT9V022=m
diff -uprN v4l-dvb.orig/v4l/Kconfig v4l-dvb.my/v4l/Kconfig
--- v4l-dvb.orig/v4l/Kconfig    2009-03-24 03:45:35.000000000 +0200
+++ v4l-dvb.my/v4l/Kconfig      2009-03-24 12:59:15.000000000 +0200
@@ -781,6 +781,13 @@ config VIDEO_VIVI
          Say Y here if you want to test video apps or debug V4L devices.
          In doubt, say N.

+config VIDEO_V4L2_LOOPBACK
+       tristate "v4l2 loopback driver"
+       depends on VIDEO_V4L2 && VIDEO_DEV
+       help
+         Say Y if you want to use v4l2 loopback driver.
+         This driver can be compiled as a module, called v4l2loopback.
+
 config VIDEO_BT848
        tristate "BT848 Video For Linux"
        depends on VIDEO_DEV && PCI && I2C && VIDEO_V4L2 && INPUT
@@ -2137,7 +2144,7 @@ config USB_S2255
        depends on VIDEO_V4L2
        select VIDEOBUF_VMALLOC
        default n
-       help
+       ---help---
          Say Y here if you want support for the Sensoray 2255 USB device.
          This driver can be compiled as a module, called s2255drv.
--
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