[libcamera-devel] [PATCH v3] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[Vedant Paranjape]

Hello Paul,
Thanks for the review.

On Fri, Jan 21, 2022 at 3:44 PM <paul.elder at ideasonboard.com> wrote:
>
> Hi Vedant,
>
> On Wed, Jan 19, 2022 at 11:25:12AM +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.
>
> + Thus, simply duplicate the checks done by vidioc_qbuf.
>
> , perhaps? You describe a (minor) issue but no solution.
>
> >
> > 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 most likely don't depend on these conditions being
> > handled correctly.
>
> Would we add these once we support importing buffers, just for
> correctness?
Sure I will do that
>
> >
> > Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> >  src/v4l2/v4l2_camera_proxy.cpp | 35 +++++++++++++++++++++++++++++++++-
> >  src/v4l2/v4l2_camera_proxy.h   |  1 +
> >  2 files changed, 35 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
> > index ec6daac605fb..f3470a6d312a 100644
> > --- a/src/v4l2/v4l2_camera_proxy.cpp
> > +++ b/src/v4l2/v4l2_camera_proxy.cpp
> > @@ -559,6 +559,38 @@ 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)
> > +             << "[" << file->description() << "] " << __func__
> > +             << "(index=" << arg->index << ")";
> > +
> > +     if (!hasOwnership(file))
> > +             return -EBUSY;
> > +
> > +     if (arg->index >= bufferCount_)
> > +             return -EINVAL;
> > +
> > +     if (arg->flags & V4L2_BUF_FLAG_REQUEST_FD)
> > +             return -EINVAL;
> > +
> > +     if (!validateBufferType(arg->type) ||
> > +         !validateMemoryType(arg->memory))
> > +             return -EINVAL;
>
> I would've said that these checks should be in the same order as in
> qbuf, but I guess you've copied this order from the kernel. In which
> case qbuf should be fixed (in a separate patch; this one's fine).
>
> > +
> > +     struct v4l2_buffer &buffer = buffers_[arg->index];
> > +
> > +     if (buffer.flags & V4L2_BUF_FLAG_QUEUED ||
> > +         buffer.flags & V4L2_BUF_FLAG_PREPARED)
> > +             return -EINVAL;
>
> Huh, I didn't realize that preparing a buf that's already been prepared
> would be an error. I thought you could just nop it. v4l2 docs haven't
> kept up I suppose :/
>
> I would say that we could check the prepared flag in qbuf too, but these
> checks are few and constant time so it's probably find as-is.
I can address this in the qbuf patch you asked above.
>
>
> Looks good.
>
> With or without the suggested changes,
>
> Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>
>
> > +
> > +     buffer.flags |= V4L2_BUF_FLAG_PREPARED;
> > +
> > +     arg->flags = buffer.flags;
> > +
> > +     return 0;
> > +}
> > +
> >  int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
> >  {
> >       LOG(V4L2Compat, Debug)
> > @@ -627,7 +659,7 @@ int V4L2CameraProxy::vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
> >
> >       struct v4l2_buffer &buf = buffers_[currentBuf_];
> >
> > -     buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE);
> > +     buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE | V4L2_BUF_FLAG_PREPARED);
> >       buf.length = sizeimage_;
> >       *arg = buf;
> >
> > @@ -729,6 +761,7 @@ 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 a38b28c744d3..76ca2d8a5558 100644
> > --- a/src/v4l2/v4l2_camera_proxy.h
> > +++ b/src/v4l2/v4l2_camera_proxy.h
> > @@ -58,6 +58,7 @@ 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);
> > --
> > 2.25.1
> >

Regards,
Vedant Paranjape