On 06/08/2015 03:35 PM, Junghak Sung wrote:
> Hello everybody,
>
> This patch series refactories exsiting Videobuf2, so that not only V4L2
> but also other frameworks can use it to manage buffer and utilize
> queue.
>
> I would separate existing Videobuf2-core framework into two parts - common
> and v4l2-specific part. This work is as follows :
>
> 1. Separate existing vb2_buffer structure into common buffer and
> v4l2-specific parts by removing v4l2-specific members and
> embedding it into vb2_v4l2_buffer structure like this:
>
> struct vb2_v4l2_buffer {
> struct vb2_buffer vb2;
> struct v4l2_buffer v4l2_buf;
> struct v4l2_plane v4l2_planes[VIDEO_MAX_PLANES];
> };
>
> 2. Abstract the v4l2-specific elements, and specify them when the device
> drives use them. For example, vb2_v4l2_buffer structure can be abstracted
> by vb2_buffer structure, and device drivers can get framework-specific
> object such as vb2_v4l2_buffer by using container_of().
>
> 3. Separate VB2-core framework into real VB2-core and v4l2-specific part.
> This means that it moves V4L2-specific parts of VB2-core to v4l2-specific
> part because current VB2-core framework has some codes dependent of V4L2.
> As a result, we will have two VB2 files - videobuf2-core.c and
> videobuf2-v4l2.c.
>
> Why do we try to make the VB2 framework to be common?
>
> As you may know, current DVB framework uses ringbuffer mechanism to demux
> MPEG-2 TS data and pass it to userspace. However, this mechanism requires
> extra memory copy because DVB framework provides only read() system call for
> application - read() system call copies the kernel data to user-space buffer.
>
> So if we can use VB2 framework which supports streaming I/O and buffer
> sharing mechanism, then we could enhance existing DVB framework by removing
> the extra memory copy - with VB2 framework, application can access the kernel
> data directly through mmap system call.
>
> This patch series is the first step for it.
>
> We have a plan for this work as follows:
>
> 1. Separate existing VB2 framework into three parts - VB2 common, VB2-v4l2,
> and VB2-dvb. Of course, this change should not affect other v4l2-based
> device drivers. This patch series includes some parts of this step.
>
> 2. Add new APIs for DVB streaming I/O. These APIs will be implemented
> in VB2-dvb framework. So, we can remove unnecessary memory copy between
> kernel-space and user-space by using these new APIs.
> However, we leaves legacy interfaces as-is for backward compatibility.
>
> We are working on this project with Mauro and have a discussion with him
> on IRC channel weekly. Nowaday, we are discussing more detailed DVB user
> scenario for streaming I/O.
>
> The final goal of this project is to enhance current DVB framework.
> The first mission is to achieve zero-copy functionality between kernel-space
> and user-space with mmap system call. More missions are under consideration:
> i.e., we could share the buffer not only between kernel-space and user-space
> but also between devices - demux, hw video codec - by exporting a buffer
> to dmabuf fd with VB2 framework.
>
> Any suggestions and comments are welcome.
>
> Best regards,
> Junghak
>
> Junghak Sung (3):
> modify the vb2_buffer structure for common video buffer and make
> struct vb2_v4l2_buffer
> move struct vb2_queue to common and apply the changes related with
> that Signed-off-by: Junghak Sung <jh1009.sung@xxxxxxxxxxx>
> make vb2-core part with not v4l2-specific elements
Patch 2/3 didn't arrive at linux-media for some reason. Can you post it again?
Thanks!
Hans
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