V4L2: What happens when the queue is full

In video capture mode, what happens when the queue is full and a new frame comes in?

Does the kernel drop frames? If so, does the newest frame (just arrived) get dropped or the oldest one in the queue gets dropped?

Answer

Yes if the queue becomes full kernel drops the buffer newest frame which just arrived, if no more buffers are available. So to avoid this you need to allocate more buffers (REQBUF) and queue back (QBUF) the buffer quickly when done in userspace.