Hello everybody,
This is the 6th round for refactoring Videobuf2(a.k.a VB2).
The purpose of this patch series is to separate existing VB2 framework
into core part and V4L2 specific part. So that not only V4L2 but also other
frameworks can use them to manage buffer and utilize queue.
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.
We have a plan for this work as follows:
1. Separate existing VB2 framework into three parts - VB2 core, VB2 v4l2.
Of course, this change will not affect other v4l2-based
device drivers. This patch series corresponds to this step.
2. Add and implement new APIs for DVB streaming I/O.
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.
This patch series is the first step for it.
The previous version of this patch series can be found at belows.
[1] RFC PATCH v1 - http://www.spinics.net/lists/linux-media/msg90688.html
[2] RFC PATCH v2 - http://www.spinics.net/lists/linux-media/msg92130.html
[3] RFC PATCH v3 - http://www.spinics.net/lists/linux-media/msg92953.html
[4] RFC PATCH v4 - http://www.spinics.net/lists/linux-media/msg93421.html
[5] RFC PATCH v5 - http://www.spinics.net/lists/linux-media/msg93810.html
Changes since v5
1. v5 is merged partially to media_tree
4 of 8 patches - restructuring vb2_buffer for common use - are merged to
media_tree. So, v6 is rebased on later version than that.
2. vb2_format is reverted to void *
vb2_format - which is newly defined for queue_setup() in v5 to deliver
the format information from user-space to device driver - is reverted to
void pointer. This change requires more discussion about the way to do
the format validation and decide the image size.
So, in this version, I would like to revert it to original version.
3. The change related with v4l2_buf_ops is moved
The change related with v4l2_buf_ops seems to be a sort of functional change.
So, it was moved to patch 3/4 - which includes the most of functional changes.
Changes since v4
1. Rebase on 4.3-rc1
Kernel 4.3-rc1 was released. So, this patch set is made based on
that version.
2. Modify queue_setup() argument
In previous patch set, struct v4l2_format, which is a parameter of
queue_setup(), is abstracted by using void pointer. But, it is better way to
pass the parameter with presise meaning than abstracting it.
So, replace void * with struct vb2_format which is newly defined to contain
the format information for common use.
3. Add a code to check if VB2_MAX_* match with VIDEO_MAX_*
Add a check code to videobuf2-v4l2.c where the compiler compares VIDEO_MAX_FRAME
and VB2_MAX_FRAME (and ditto for MAX_PLANES) and throws an #error if they
do not match.
4. Change the commit order
For easier review, the patch that just move things around without doing any
functional change is moved to the last.
All ideas above are from Hans and it seems to be better and right way.
Changes since v3
1. Resolve build errors
In previous patch set, the build errors prevented reviewers from applying
the patch. So, in this patch, I tryed to fix the build errors but I hadn't
the build test on all architectures except for x86 and ARM.
2. Modify descriptions for DocBook
Descriptions not complying with the DocBook rule are modified,
which was pointed out by Mauro.
3. Initialize reserved fields explicitly
The reserved fields of v4l2_buffer are initialized by 0 explicitly
when the vb2_buffer information is returned to userspace,
which was pointed out by Hans.
4. Remove unnecessary type-cast
According to Mauro's advice, the unnecessary type-cast are removed
because it's better for the compiler - rather than human - to check those
things.
5. Sperate the patch - not easy to review - into two patches
In previous patch set, patch 5 was too difficult to review. So accoring to
Hans' opinion, it separated the patch without any functional changes.
Changes since v2
1. Remove v4l2 stuffs completely from vb2_buffer
The v4l2 stuffs - v4l2_buf and v4l2_planes - are removed completely from
struct vb2_buffer. New member variables - index, type, memory - are added
to struct vb2_buffer, all of which can be used commonly. And bytesused,
length, offset, userptr, fd, data_offset are added to struct vb2_plane
for the same reason. So, we can manage video buffer by only using
struct vb2_buffer.
And, v4l2 stuffs - flags, field, timestamp, timecode, sequence - are defined
as member variables of struct vb2_v4l2_buffer.
2. Create new header file for VB2 internal use
videobuf2-internal.h is created, which is referred by videobuf2-core
and videobuf2-v4l2. The header file contains dprintk() for debug,
macro functions to invoke various callbacks, and vb2_core_* function prototypes
referred by inside of videobuf2.
3. Remove buffer-specific callbacks as much as possible
There were many callback functions to handle video buffer information
in previous patch series. In this patch series, I try to remove these callbacks
as much as possible without breaking the existing function flow.
As a result, only four callbacks are remained - fill_user_buffer(),
fill_vb2_buffer(), fill_vb2_timestamp() and is_last().
All ideas above are from Hans and it seems to be better and right way.
Changes since v1
1. Divide patch set into more pieces
v1 was not reviewed normally because the 2/3 patch is failed to send to mailing
list with size problem - over 300kb. So I have divided the patch set into five
pieces and refined them neatly, which was pointed by Hans.
2. Add shell scripts for renaming patch
In case of renaming patch, shell scripts are included inside the body of the
patches by Mauro's advice. 1/5 and 5/5 patches include these scripts, which can
be used by reviewers or maintainers to regenerate big patch file if something
goes wrong during patch apply.
3. Remove dependency on v4l2 from videobuf2
In previous patch set, videobuf2-core uses v4l2-specific stuff as it is.
e.g. enum v4l2_buf_type and enum v4l2_memory. That prevented other frameworks
from using videobuf2 independently and made them forced to include
v4l2-specific stuff.
In this version, these dependent stuffs are replaced with VB2 own stuffs.
e.g. enum vb2_buf_type and enum vb2_memory. So, v4l2-specific header file isn't
required to use videobuf2 in other modules. Please, note that videobuf2 stuffs
will be translated to v4l2-specific stuffs in videobuf2-v4l2.c file for
backward compatibility.
4. Unify duplicated definitions
VB2_DEBUG() is newly defined in videobuf2-core header file in order to unify
duplicated macro functions that invoke callback functions implemented in vb2
backends - i.e., videobuf2-vmalloc and videobuf2-dma-sg - and queue relevant
callbacks of device drivers.
In previous patch set, these macro functions were defined
in both videobuf2-core.c and videobuf2-v4l2.c.
This patch series is based on media_tree.git [6]. I have applied this patches
to my own git [7] for review, and tested this patch series on ubuntu
PC(Intel i7-3770) for x86 system and odroid-xu3(exynos5422) for ARM.
[6] media_tree.git - http://git.linuxtv.org/cgit.cgi/media_tree.git/
[7] jsung/dvb-vb2.git - http://git.linuxtv.org/cgit.cgi/jsung/dvb-vb2.git/
(branch: vb2-refactoring)
Any suggestions and comments are welcome.
Regards,
Junghak
