This leads me into the next point/question regarding output devices.
Wouldn't it be better to have output demux devices such as PID filter,
recording filter, section filter, decoder feed with each one allocated a
different minor number. Then when the user app came to open up an fd on
this device, we would know immediately if we had enough
resources/filters/feeds left to allow the "open" syscall to succeed. At
the moment we open up an fd, but we don't know what the underlying usage of
it is going to be until we perform one of the demux IOCTLs to setup a
feed/filter. Only here, is when we know whether we can actually get a
handle to a feed/filter. Not really that elegant is it?
Just a short answer: most hardware doesn't have dedicated units for
these tasks, so you cannot say for sure that you have x recording
filters or y pid filters available. With these chipsets, opening a
device can easily fail because resources are lacking.