Re: [PATCH 6/7] [media] gspca: fix a v4l2-compliance failure during VIDIOC_REQBUFS

[Antonio Ospite <ao2@ao2.it>]

On Thu, 10 Mar 2016 15:54:37 +0100
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 09-03-16 17:03, Antonio Ospite wrote:
> > When calling VIDIOC_REQBUFS v4l2-compliance fails with this message:
> >
> >    fail: v4l2-test-buffers.cpp(476): q.reqbufs(node, 1)
> >    test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: FAIL
> >
> > By looking at the v4l2-compliance code the failure happens when trying
> > to request V4L2_MEMORY_USERPTR buffers without freeing explicitly the
> > previously allocated V4L2_MEMORY_MMAP buffers.
> >
> > This would suggest that when changing the memory field in struct
> > v4l2_requestbuffers the driver is supposed to free automatically any
> > previous allocated buffers, and looking for inspiration at the code in
> > drivers/media/v4l2-core/videobuf2-core.c::vb2_core_reqbufs() seems to
> > confirm this interpretation; however gspca is just returning -EBUSY in
> > this case.
> >
> > Removing the special handling for the case of a different memory value
> > fixes the compliance failure.
> >
> > Signed-off-by: Antonio Ospite <ao2@ao2.it>
> > ---
> >
> > This should be safe, but I'd really like a comment from someone with a more
> > global knowledge of v4l2.
> >
> > If my interpretation about how drivers should behave when the value of the
> > memory field changes is correct, I could send also a documentation update for
> > Documentation/DocBook/media/v4l/vidioc-reqbufs.xml
> >
> > Just let me know.
> >
> > Thanks,
> >     Antonio
> >
> >
> >   drivers/media/usb/gspca/gspca.c | 7 -------
> >   1 file changed, 7 deletions(-)
> >
> > diff --git a/drivers/media/usb/gspca/gspca.c b/drivers/media/usb/gspca/gspca.c
> > index 84b0d6a..915b6c7 100644
> > --- a/drivers/media/usb/gspca/gspca.c
> > +++ b/drivers/media/usb/gspca/gspca.c
> > @@ -1402,13 +1402,6 @@ static int vidioc_reqbufs(struct file *file, void *priv,
> >   	if (mutex_lock_interruptible(&gspca_dev->queue_lock))
> >   		return -ERESTARTSYS;
> >
> > -	if (gspca_dev->memory != GSPCA_MEMORY_NO
> > -	    && gspca_dev->memory != GSPCA_MEMORY_READ
> > -	    && gspca_dev->memory != rb->memory) {
> > -		ret = -EBUSY;
> > -		goto out;
> > -	}
> > -
> 
> reqbufs is used internally and this change will allow changing
> gspca_dev->memory from USERPTR / MMAP to GSPCA_MEMORY_READ
> please replace this check with a check to only allow
> rb->memory to be GSPCA_MEMORY_READ when coming from GSPCA_MEMORY_NO
> or GSPCA_MEMORY_READ
> 

OK, thanks, I'll take a look again later this week.

In the meantime, if patches from 1 to 5 are OK, can we have them merged
so I will just resubmit the last two in the set?

Ciao,
   Antonio

-- 
Antonio Ospite
http://ao2.it

A: Because it messes up the order in which people normally read text.
   See http://en.wikipedia.org/wiki/Posting_style
Q: Why is top-posting such a bad thing?