[libcamera-devel] [PATCH v1] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[Vedant Paranjape]

Hello Laurent,


On Wed, Jan 12, 2022 at 12:52 AM Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> On Tue, Jan 11, 2022 at 09:10:53PM +0200, Laurent Pinchart wrote:
> > Hi Vedant,
> >
> > Thank you for the patch.
> >
> > On Tue, Jan 11, 2022 at 10:03:29PM +0530, Vedant Paranjape wrote:
> > > Add support for PREPARE_BUF as one of the ioctl. Since this is a compat
> > > layer, there doesn't seem to be an equivalent to the "transfer ownership
> > > of the buffer to kernel driver" in V4L2Camera class.
> > >
> > > To match the error checks done by kernel implementation, we'd have to
> > > check if dmabuf fd is valid and that the buffer size is large enough.
> > > Doing so will not add any particular value to the program as
> > > applications don't depend on these conditions being handled correctly.
> >
> > s/don't depend/most likely don't depend/ (there can always be corner
> > cases, developers sometimes get inventive)
> >
> > > Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
> > > ---
> > > Source builds and tests fine, also passes the v4l2-compliance
> > >
> > > <snip>
> > > vedant at pc ~/libcamera$ ./test/v4l2_compat/v4l2_compat_test.py ./build/src/v4l2/v4l2-compat.so
> > > Testing /dev/video0 with uvcvideo driver... success
> > > </snip>
> > >
> > > Still figuring out how to test this with v4l2-ctl, if you have hints
> > > please let me know :)
> >
> > v4l2-compliance tests VIDIOC_PREPARE buf, that should be good enough as
> > a test.
> >
> > > ---
> > > src/v4l2/v4l2_camera_proxy.cpp | 28 ++++++++++++++++++++++++++++
> > >  src/v4l2/v4l2_camera_proxy.h   |  1 +
> > >  2 files changed, 29 insertions(+)
> > >
> > > diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
> > > index 4d529bc29a4d..8c28e8738a06 100644
> > > --- a/src/v4l2/v4l2_camera_proxy.cpp
> > > +++ b/src/v4l2/v4l2_camera_proxy.cpp
> > > @@ -544,6 +544,33 @@ int V4L2CameraProxy::vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *a
> > >     return 0;
> > >  }
> > >
> > > +int V4L2CameraProxy::vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg)
> > > +{
> > > +   LOG(V4L2Compat, Debug) << "Servicing vidioc_prepare_buf, index = "
> > > +                          << arg->index << " fd = " << file->efd();
> > > +
> > > +   if (!hasOwnership(file))
> > > +           return -EBUSY;
> > > +
> > > +   if (arg->index >= bufferCount_)
> > > +           return -EINVAL;
> > > +
> >
> >       struct v4l2_buffer &buffer = buffers_[arg->index];
> >
> > and use buffer below.
> >
> > With this change, and v4l2-compliance passing,
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >
> > > +   if (buffers_[arg->index].flags & V4L2_BUF_FLAG_REQUEST_FD ||
>
> Actually, this isn't correct, you need to check arg->flags here.

I missed this, but I can't figure out the reason why this is incorrect ?

> > > +       buffers_[arg->index].flags & V4L2_BUF_FLAG_PREPARED)
> > > +           return -EINVAL;
> > > +
> > > +   if (buffers_[arg->index].flags & V4L2_BUF_FLAG_QUEUED ||
> > > +       !validateBufferType(arg->type) ||
> > > +       !validateMemoryType(arg->memory))
> > > +           return -EINVAL;
>
> And let's group all the flags check:
>
>         if (arg->flags & V4L2_BUF_FLAG_REQUEST_FD)
>                 return -EINVAL;
>
>         if (!validateBufferType(arg->type) || !validateMemoryType(arg->memory))
>                 return -EINVAL;
>
>         struct v4l2_buffer &buffer = buffers_[arg->index];
>
>         if (buffer.flags & V4L2_BUF_FLAG_PREPARED ||
>             buffer.flags & V4L2_BUF_FLAG_QUEUED ||
>                 return -EINVAL;
>
> > > +
> > > +   buffers_[arg->index].flags |= V4L2_BUF_FLAG_PREPARED;
> > > +
> > > +   arg->flags = buffers_[arg->index].flags;
> > > +
> > > +   return 0;
> > > +}
> > > +
> > >  int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
> > >  {
> > >     LOG(V4L2Compat, Debug) << "Servicing vidioc_qbuf, index = "
> > > @@ -709,6 +736,7 @@ const std::set<unsigned long> V4L2CameraProxy::supportedIoctls_ = {
> > >     VIDIOC_S_INPUT,
> > >     VIDIOC_REQBUFS,
> > >     VIDIOC_QUERYBUF,
> > > +   VIDIOC_PREPARE_BUF,
> > >     VIDIOC_QBUF,
> > >     VIDIOC_DQBUF,
> > >     VIDIOC_EXPBUF,
> > > diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
> > > index 14e027c3e7d1..6baba94262a9 100644
> > > --- a/src/v4l2/v4l2_camera_proxy.h
> > > +++ b/src/v4l2/v4l2_camera_proxy.h
> > > @@ -57,6 +57,7 @@ private:
> > >     int vidioc_s_input(V4L2CameraFile *file, int *arg);
> > >     int vidioc_reqbufs(V4L2CameraFile *file, struct v4l2_requestbuffers *arg);
> > >     int vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
> > > +   int vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg);
> > >     int vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
> > >     int vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
> > >                      libcamera::Mutex *lock) LIBCAMERA_TSA_REQUIRES(*lock);
>
> --
> Regards,
>
> Laurent Pinchart

Regards,
Vedant Paranjape