[linux-dvb] Re: V4 API proposal

[Johannes Stezenbach <js@convergence.de>]

On Wed, Mar 19, 2003 at 03:42:40PM +0100, Haber, Thomas wrote:
> Hi Johannes,
> 
> i'm still not sure about it.
> 
> > I've spent some time thinking about this. IMHO the most 
> > "natural" approach
> > would be to use the demux file descriptor where you have set the
> > appropriate filters, e.g. for video PES, and pass it to the SET_SOURCE
> > ioctl for e.g. the video MPEG decoder.
> > 
> Yes, but what about connecting the demux to the frontend ?
> In the same way ?
> I would prefer to do all the connection in the same style.

It would be more consistent to do so, but on a functional level
it seems unnecessary because the frontend output can only go to
the demux, and there will only be a very limited number of frontends
in a system. So for DMX_SET_SOURCE it will be sufficient to specify
the frontend _number_.

For the demux outputs it's entirely different, because there
are many of them, and they have no natural identification number
associated with them.

> > > How do we setup user area bridges ? (to override hardware barriers)
> > >  * a thread reading and writing ??? for sure not appropriate for 
> > >    streams from the frontend but for other streams it is
> > 
> > This is an implementation detail that would have to be solved in
> > an individual device driver. Bridging via copy-to-userspace-and-back
> > should be avoided, yes?
> 
> What about drivers that don't know each other (differnt hardware - one
> demux, one decoder)? 

What I meant to say is that we would probably want to have
support for copying data within the kernel/driver, without
having to copy data to userspace from one driver and back into
the kernel to the other driver. E.g. VDR currently does a lot
of copying in "transfer mode", and it works fine, but it's not
particularly efficient.

A more interesting related issue is bridging the gap between
demux input/output and HDD read/write. With all of linux' filesystem
stuff in between this will be challenging.

Still, it is not important to decide how to implement it, or even
*if* to implement it. It's just that the API should allow for it
to be implemented.


Johannes


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