[linux-dvb] LinuxDVB V4 API questions (3)

[Alasdair FARMER <alasdair.farmer@st.com>]

Couple more questions...

1)  I have a concern from a robustness perspective about the way in which connections between demux's and decoders is handled.  If we assume that we have a demux feeding a decoder, through a mmapped buffer.  What happens if the file handle on the demux/filter is closed ?  As I understand it this will result in the buffer 'disappearing' as it is allocated/freed by the demux for the filter on that instance.  BUT what about the decoder - this could still be trying to decode from the buffer in ignorance that the buffer is no longer there/valid...  True, it would be possible for the decoder to check the file handle on every operation - but this is overhead you really do not want.  I would like to see some kind of back linking to allow the demux to tell the decoder that it is closing down.  I realise this is mainly a robustness issue - but one I think worth implementing.

2)  With regard to playback of recordings I am unclear how this will work in the new model...  If a recorded stream were being written to a demux then which instance (given that the handle is actually to a filter rather than a demux itself).  I am not convinced that a memory frontend is the correct or best solution.  The semantic model I am working with is that the frontend is providing a transport stream to a demux which is filtering and passing the appropriate sub streams on to a decoder/storage.  The frontend is responsible for presenting a single transport stream to the demux, dealing with any issues of source or routing.  I would actually like to see a write interface on the frontend so that a recorded stream could be written to a frontend (rather than the stream come from a tuner).  This neatly maintains a consistent model and removes some complexity at demux level.  In our scenarios, it is not actually possible to 'write' to a demux anyway, a recorded stream would have to be feed back into what is essentially a frontend - so for our hardware solutions, we would need a write api on a frontend anyway.  This also simplifies CA considerations.

I await your comments with interest.

Regards

Ali Farmer.






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