[Linaro-mm-sig] [RFC] dma-shared-buf: Add buffer sharing framework

[Clark, Rob]

On Fri, Aug 26, 2011 at 4:06 AM, Hans Verkuil <hverkuil at xs4all.nl> wrote:
>
> Frankly, I'm not sure about the read and write. I don't really see the use
> case. The whole point of buffer sharing is to avoid copying buffers, and that's
> exactly what read and write do.
>

The main point (and maybe there is no point) for read/write is an
alternative interface for sw access to buffer..  it isn't really
intended for performant use cases, but rather for edge-cases.  Like
when we want to grab one frame of video and use sw to generate a
thumbnail.

Possibly mmap interface would be fine.  But read/write seems
attractive because you could do an easier job of hiding some weird
formats.  (Which I suppose you could still do w/ mmap and fault
handling games.)

I don't have any immediate plans for such use (mmap would suffice),
but it did seem good to have all the normal file ops supported.  If
someone passed me a fd in userspace, I would expect to be able to
read() and write(), and would be a bit surprised if that wasn't
supported.  So I guess principle-of-least-surpise applies here.

BR,
-R