Re: [PATCH] qcap: fix recent regression that limited Wine's v4l2 support to devices that read()

[Damjan Jovanovic]

On Sat, Apr 20, 2019 at 7:08 PM Zebediah Figura 
wrote:
> On 4/20/19 11:55 AM, Damjan Jovanovic wrote:
> > On Sat, Apr 20, 2019 at 6:07 PM Zebediah Figura <[e-mail]
> > > wrote:
> > On 4/20/19 10:56 AM, Damjan Jovanovic wrote:
> >  >
> >  >
> >  > On Sat, Apr 20, 2019 at 5:44 PM Zebediah Figura
> > <[e-mail] <mailto:[e-mail]>
> >  > <mailto:[e-mail] <mailto:[e-mail]>>>
>
> wrote:
> >  >
> >  >     On 4/20/19 10:31 AM, Damjan Jovanovic wrote:
> >  >      >
> >  >      >
> >  >      > On Sat, Apr 20, 2019 at 4:52 PM Zebediah Figura
> >  >     <[e-mail] <mailto:[e-mail]>
> > <mailto:[e-mail] <mailto:[e-mail]>>
> >  >      > <mailto:[e-mail] <mailto:[e-mail]>
> > <mailto:[e-mail] <mailto:[e-mail]>>>> wrote:
> >  >      >
> >  >      >     On 4/20/19 8:15 AM, Damjan Jovanovic wrote:
> >  >      >      > Recent changes to qcap/v4l.c resulted in the
> > removal of mmap()
> >  >      >      > for v4l2 devices, but read() is optional for device
> >  >     drivers and
> >  >      >      > some don't support it. This isn't a major problem
> > with the
> >  >      >      > presense of libv4l2 though, as it can emulate
> > read() on top of
> >  >      >      > mmap(). However the code checks whether the device
> > can read(),
> >  >      >      > and if not, doesn't even try to use it, even though
> > it can.
> >  >      >      >
> >  >      >      > Fix this by only warning that read() is being
> > emulated, and
> >  >      >      > continuing with libv4l2 if available.
> >  >      >      >
> >  >      >      > Also clarifies the logging.
> >  >      >      >
> >  >      >      > Signed-off-by: Damjan Jovanovic
> > <[e-mail] <mailto:[e-mail]>
> >  >     <mailto:[e-mail] <mailto:[e-mail]>>
> >  >      >     <mailto:[e-mail]
> > <mailto:[e-mail]> <mailto:[e-mail]
> > <mailto:[e-mail]>>>>
> >  >      >      > ---
> >  >      >      >   dlls/qcap/v4l.c | 13 ++++++++-----
> >  >      >      >   1 file changed, 8 insertions(+), 5 deletions(-)
> >  >      >      >
> >  >      >      >
> >  >      >      >
> >  >      >
> >  >      >     This doesn't seem right; libv4l2 should massage the
> > result of
> >  >      >     VIDIOC_QUERYCAP to include V4L2_CAP_READWRITE. See
> >  >      >
> >  >
> >   <
>
> https://git.linuxtv.org/v4l-utils.git/tree/lib/libv4l2/libv4l2.c#n1210%3E.
> >  >      >
> >  >      >
> >  >      > On FreeBSD 11.2 with libv4l-1.6.3_4, that is certainly NOT
>
> the
> >  >     case. It
> >  >      > could be a newer or not yet released feature.
> >  >      >
> >  >      >
> >  >      >
> >  >
> >  >     It's been the case since libv4l2 0.5:
> >  >
> >   <
>
> https://git.linuxtv.org/v4l-utils.git/commit/lib/libv4l2/libv4l2.c?id=0215f2...
> >  >
> >  >     If FreeBSD is using 1.6.3, then I think something else is
> > wrong. Are
> >  >     you
> >  >     sure that libv4l2 is actually being loaded?
> >  >
> >  >
> >  > int v4l2_ioctl(int fd, unsigned long int request, ...)
> >  > {
> >  > ...
> >  >          if (devices[index].convert == NULL)
> >  >                  goto no_capture_request;
> >  >
> >  > <your code nippet from above>
> >  >
> >  > no_capture_request:
> >  >
> >  >
> >  >
> >  > So the code that would set that flag, is skipped if the .convert
> > field
> >  > is NULL.
> >  >
> >  > When is it NULL?
> >  >
> >  >
> >  >
> >
> > If my reading of the code is correct, only when v4l2_fd_open() is
> > called
> > manually with V4L2_DISABLE_CONVERSION. Obviously we don't do that.
> >
> > Perhaps setting LIBV4L2_LOG_FILENAME might give some hints as to
>
> what's
> > going wrong?
> >
> >
> >
> > int v4l2_fd_open(int fd, int v4l2_flags)
> > {
> > ...
> > <The actual ioctl() returns cap.capabilities = 0x84a00001,
> > cap.device_caps = 0x04a00000>
> >      if (cap.capabilities & V4L2_CAP_DEVICE_CAPS)
> >              cap.capabilities = cap.device_caps;
> >      if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) ||
> >          !(cap.capabilities & (V4L2_CAP_STREAMING |
> >
> > V4L2_CAP_READWRITE))) {
> >                  goto no_capture;
> >          }
> >
> > 0x000000001 = V4L2_CAP_VIDEO_CAPTURE
> > 0x00200000 = V4L2_CAP_EXT_PIX_FORMAT
> > 0x00800000 = V4L2_CAP_META_CAPTURE
> > 0x040000000 = V4L2_CAP_STREAMING
> > 0x800000000 = V4L2_CAP_DEVICE_CAPS
> >
> > So cap.capabilities have all those flags set, but cap.device_caps lacks
> > V4L2_CAP_VIDEO_CAPTURE.
> > cap.capabilities is overwritten by cap.device_caps, thus
> > V4L2_CAP_VIDEO_CAPTURE is cleared.
> > Since libv4l2 only manages devices with V4L2_CAP_VIDEO_CAPTURE set, and
> > that flag is now missing, the first condition in the next "if" takes the
> > goto, and .convert remains NULL.
> > With .convert NULL, libv4l2 no longer manages the device, so
> > communication is directly between Wine and kernel.
> > Therefore the V4L2_CAP_READWRITE flag is not going to be set in
> > v4l2_ioctl(), and libv4l2 cannot be made to do any conversions for us.
> > But then again we can't use a device without V4L2_CAP_VIDEO_CAPTURE
> > either, libv4l2 or not.
> >
> > I think the fundamental problem is that Wine is trying to use
> > /dev/video1 which is broken, due to a bug in devenum that overwrites the
> > working /dev/video0 registry entry with it, because their descriptions
> > are the same.
>
> Thanks, I've just sent patches to resolve both of these bugs.

Wow, so quickly!

Thank you!