V4L2: handle device capabilities correctly

cap.capabilities describes all capabilities of the whole physical device.
It may contain V4L2_CAP_VIDEO_CAPTURE and V4L2_CAP_VIDEO_OUTPUT if multiple
/dev/video* device nodes are part of the same physical device.
If the V4L2_CAP_DEVICE_CAPS flag is set, then device_caps contains the
capabilities of the currently opened device node.
So this should be checked as well to determine if the device node is a
capture device.

Bug: None
Change-Id: I83c0516c546121a0fac82380b72d1c8f3cb22fc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2537967Reviewed-by: Shik Chen <shik@chromium.org>
Commit-Queue: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828754}

media/capture/video/linux/v4l2_capture_delegate.cc

@@ -264,10 +264,18 @@ void V4L2CaptureDelegate::AllocateAndStart(
 
   ResetUserAndCameraControlsToDefault();
 
+  // In theory, checking for CAPTURE/OUTPUT in caps.capabilities should only
+  // be done if V4L2_CAP_DEVICE_CAPS is not set. However, this was not done
+  // in the past and it is unclear if it breaks with existing devices. And if
+  // a device is accepted incorrectly then it will not have any usable
+  // formats and is skipped anyways.
   v4l2_capability cap = {};
   if (!(DoIoctl(VIDIOC_QUERYCAP, &cap) == 0 &&
-        ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) &&
-         !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT)))) {
+        (((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) &&
+          !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT)) ||
+         ((cap.capabilities & V4L2_CAP_DEVICE_CAPS) &&
+          (cap.device_caps & V4L2_CAP_VIDEO_CAPTURE) &&
+          !(cap.device_caps & V4L2_CAP_VIDEO_OUTPUT))))) {
     device_fd_.reset();
     SetErrorState(VideoCaptureError::kV4L2ThisIsNotAV4L2VideoCaptureDevice,
                   FROM_HERE, "This is not a V4L2 video capture device");

media/capture/video/linux/video_capture_device_factory_linux.cc

@@ -205,10 +205,18 @@ void VideoCaptureDeviceFactoryLinux::GetDevicesInfo(
     // one supported capture format. Devices that have capture and output
     // capabilities at the same time are memory-to-memory and are skipped, see
     // http://crbug.com/139356.
+    // In theory, checking for CAPTURE/OUTPUT in caps.capabilities should only
+    // be done if V4L2_CAP_DEVICE_CAPS is not set. However, this was not done
+    // in the past and it is unclear if it breaks with existing devices. And if
+    // a device is accepted incorrectly then it will not have any usable
+    // formats and is skipped anyways.
     v4l2_capability cap;
     if ((DoIoctl(fd.get(), VIDIOC_QUERYCAP, &cap) == 0) &&
-        (cap.capabilities & V4L2_CAP_VIDEO_CAPTURE &&
-         !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT)) &&
+        ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE &&
+          !(cap.capabilities & V4L2_CAP_VIDEO_OUTPUT)) ||
+         (cap.capabilities & V4L2_CAP_DEVICE_CAPS &&
+          cap.device_caps & V4L2_CAP_VIDEO_CAPTURE &&
+          !(cap.device_caps & V4L2_CAP_VIDEO_OUTPUT))) &&
         HasUsableFormats(fd.get(), cap.capabilities)) {
       const std::string model_id =
           device_provider_->GetDeviceModelId(unique_id);