[linux-dvb] CI implementation question

[Andrew de Quincey <adq_dvb@lidskialf.net>]

I'm in the middle of implementing a generic set of driver functions for 
talking to budget-style CI interfaces (slot monitoring, CAM initialisation, 
and the link level protocol). I have a question about reading and writing 
data to the command interface.

CENELEC EN50221 implies that you can't write data to the CAM if it has data 
waiting to be read by the host. What have other people's implementations done 
if a user app attempts to write() data when it is not possible?

I could cache the data to be written... I don't like this... the app might 
never read().
I could return EAGAIN.
I could return 0 as the number of bytes written.

Anyone got any suggestions? I want to be as compatable with existing 
user-space libraries as possible. 


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