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

[Zebediah Figura]

On 4/20/19 11:55 AM, Damjan Jovanovic wrote:
> 
> 
> On Sat, Apr 20, 2019 at 6:07 PM Zebediah Figura <z.figura12 at gmail.com 
> <mailto:z.figura12 at gmail.com>> wrote:
> 
>     On 4/20/19 10:56 AM, Damjan Jovanovic wrote:
>      >
>      >
>      > On Sat, Apr 20, 2019 at 5:44 PM Zebediah Figura
>     <z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>
>      > <mailto:z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>>> wrote:
>      >
>      >     On 4/20/19 10:31 AM, Damjan Jovanovic wrote:
>      >      >
>      >      >
>      >      > On Sat, Apr 20, 2019 at 4:52 PM Zebediah Figura
>      >     <z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>
>     <mailto:z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>>
>      >      > <mailto:z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>
>     <mailto:z.figura12 at gmail.com <mailto:z.figura12 at gmail.com>>>> 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
>     <damjan.jov at gmail.com <mailto:damjan.jov at gmail.com>
>      >     <mailto:damjan.jov at gmail.com <mailto:damjan.jov at gmail.com>>
>      >      >     <mailto:damjan.jov at gmail.com
>     <mailto:damjan.jov at gmail.com> <mailto:damjan.jov at gmail.com
>     <mailto:damjan.jov at gmail.com>>>>
>      >      >      > ---
>      >      >      >   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>.
>      >      >
>      >      >
>      >      > 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=0215f2ac08c3ad0dc66ad8036f4e186a5e8f56d6>
>      >
>      >     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.