Hi Hans, On Thursday, 15 November 2018 09:30:55 EET Hans Verkuil wrote: > On 11/14/2018 08:52 PM, Laurent Pinchart wrote: > > On Tuesday, 13 November 2018 17:43:48 EET Hans Verkuil wrote: > >> On 11/13/18 16:06, Philipp Zabel wrote: > >>> From: John Sheu <sheu@xxxxxxxxxxxx> > >>> > >>> Videobuf2 presently does not allow VIDIOC_REQBUFS to destroy outstanding > >>> buffers if the queue is of type V4L2_MEMORY_MMAP, and if the buffers are > >>> considered "in use". This is different behavior than for other memory > >>> types and prevents us from deallocating buffers in following two cases: > >>> > >>> 1) There are outstanding mmap()ed views on the buffer. However even if > >>> we put the buffer in reqbufs(0), there will be remaining references, > >>> due to vma .open/close() adjusting vb2 buffer refcount appropriately. > >>> This means that the buffer will be in fact freed only when the last > >>> mmap()ed view is unmapped. > >>> > >>> 2) Buffer has been exported as a DMABUF. Refcount of the vb2 buffer > >>> is managed properly by VB2 DMABUF ops, i.e. incremented on DMABUF > >>> get and decremented on DMABUF release. This means that the buffer > >>> will be alive until all importers release it. > >>> > >>> Considering both cases above, there does not seem to be any need to > >>> prevent reqbufs(0) operation, because buffer lifetime is already > >>> properly managed by both mmap() and DMABUF code paths. Let's remove it > >>> and allow userspace freeing the queue (and potentially allocating a new > >>> one) even though old buffers might be still in processing. > >>> > >>> To let userspace know that the kernel now supports orphaning buffers > >>> that are still in use, add a new V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS > >>> to be set by reqbufs and create_bufs. > >> > >> Looks good, but I have some questions: > >> > >> 1) does v4l2-compliance together with vivid (easiest to test) still work? > >> I don't think I have a proper test for this in v4l2-compliance, but > >> I'm not 100% certain. If it fails with this patch, then please provide > >> a fix for v4l2-compliance as well. > >> > >> 2) I would like to see a new test in v4l2-compliance for this: i.e. if > >> the capability is set, then check that you can call REQBUFS(0) before > >> unmapping all buffers. Ditto with dmabuffers. > >> > >> I said during the media summit that I wanted to be more strict about > >> requiring compliance tests before adding new features, so you're the > >> unlucky victim of that :-) > > > > Do you have plans to refactor and document the v4l2-compliance internals > > to make it easier ? > > Yes. I hope to be able to set aside one or two days for that in the next two > weeks. That would be great ! Let me know if you would like to discuss how the code base could be refactored. -- Regards, Laurent Pinchart
