[media] v4l: videobuf2: add read() and write() emulator

Add a generic file io (read and write) emulator for videobuf2. It uses
MMAP memory type buffers and generic vb2 calls: req_bufs, qbuf and
dqbuf. Video date is being copied from mmap buffers to userspace with
standard copy_to_user() function. To add support for file io the driver
needs to provide an additional callback - read_setup or write_setup. It
should provide the default number of buffers used by emulator and flags.

With these flags one can detemine the style of read() or write()
emulation. By default 'streaming' style is used. With
VB2_FILEIO_READ_ONCE flag one can select 'one shot' mode for read()
emulator. With VB2_FILEIO_WRITE_IMMEDIATE flag one can select immediate
conversion of write calls to qbuf for write() emulator, so the vb2 will
not wait until each buffer is filled completely before queueing it to
the driver.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
CC: Pawel Osciak <pawel@osciak.com>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/videobuf2-core.h

@@ -18,6 +18,7 @@
 #include <linux/videodev2.h>
 
 struct vb2_alloc_ctx;
+struct vb2_fileio_data;
 
 /**
  * struct vb2_mem_ops - memory handling/memory allocator operations
@@ -54,6 +55,7 @@ struct vb2_alloc_ctx;
  *
  * Required ops for USERPTR types: get_userptr, put_userptr.
  * Required ops for MMAP types: alloc, put, num_users, mmap.
+ * Required ops for read/write access types: alloc, put, num_users, vaddr
  */
 struct vb2_mem_ops {
 	void		*(*alloc)(void *alloc_ctx, unsigned long size);
@@ -249,6 +251,7 @@ struct vb2_ops {
  * @done_wq:	waitqueue for processes waiting for buffers ready to be dequeued
  * @alloc_ctx:	memory type/allocator-specific contexts for each plane
  * @streaming:	current streaming state
+ * @fileio:	file io emulator internal data, used only if emulator is active
  */
 struct vb2_queue {
 	enum v4l2_buf_type		type;
@@ -275,6 +278,8 @@ struct vb2_queue {
 	void				*alloc_ctx[VIDEO_MAX_PLANES];
 
 	unsigned int			streaming:1;
+
+	struct vb2_fileio_data		*fileio;
 };
 
 void *vb2_plane_vaddr(struct vb2_buffer *vb, unsigned int plane_no);
@@ -298,6 +303,10 @@ int vb2_streamoff(struct vb2_queue *q, enum v4l2_buf_type type);
 
 int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma);
 unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait);
+size_t vb2_read(struct vb2_queue *q, char __user *data, size_t count,
+		loff_t *ppos, int nonblock);
+size_t vb2_write(struct vb2_queue *q, char __user *data, size_t count,
+		loff_t *ppos, int nonblock);
 
 /**
  * vb2_is_streaming() - return streaming status of the queue