I'm writing a python library called linuxpy which supports V4L2.
One of the features is being able to open de V4L2 device in non blocking mode (O_NONBLOCK) to be cooperative with python async/await.
I tried with several real cameras and everything seems to work properly.
But when I test v4l2loopback device it blocks waiting for the first frame if I open the v4l2loopback device with O_NONBLOCK.
Does anyone know if v4l2loopback supports O_NONBLOCK?
This is a bug in v4l2loopback where poll would (always) block if the first call to poll occurred while the device was in a 'readable' state.
In v4l2loopback's implementation of poll, it did not call poll_wait if the device was in a readable state. This has a side effect if the device was readable the first time poll was called: subsequent calls to poll_wait on the table become no-ops; and thus poll will block. See: https://github.com/torvalds/linux/commit/726daf6 for a similar example.
