[linux-dvb] Re: Two more DVB CA IOCTL questions

[Johannes Stezenbach <js@convergence.de>]

Andrew de Quincey wrote:
> A couple more DVB CA IOCTL questions have occurred to me, and need cleared up:
> 
> 1) Should the CA_GET_MSG and CA_SEND_MSG ioctls block? Currently the 
> read()/write() interface blocks if there isn't any data/enough buffer space 
> for the message. My feeling is no, and I should return -EAGAIN (or 
> equivalent) for the IOCTLs.

IMHO it should depend on O_NONBLOCK for both the ioctls and read/write.

> 2) Should CA_GET_MSG receive from ANY slot/connection (i.e. overwrite any user 
> passed parameters), or should it only receive from the slot/connection 
> supplied in the sructure.
> 
> I ask this because the read() interface just returns packets from all 
> slots/connections. My feeling is it should be possible to select, but also to 
> specify ANY (e.g. pass -1 for either parameter). In this case, the 
> parameter(s) in the ca_msg_t structure will be overwritten with the 
> appropriate value. This kind of filtering is very easy with the kernel data 
> structures I've defined.

I think applications / libdvbci want to get messages from ANY slot
and dispatch them to the upper protocol layers. If you could
specify a slot # for CA_GET_MSG then you need separate buffers
in the driver, and that's IMHO not necessary.

Johannes


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