Re: DVB mmap API

[Mauro Carvalho Chehab <mchehab@kernel.org>]

Em Sat, 8 Jan 2022 12:34:59 -0500
Adam Stylinski <kungfujesus06@gmail.com> escreveu:

> Hello,
> 
> I'm probably just looking for a project of unnecessary complexity to
> take on but I couldn't help but notice there's been driver support for
> mmap on DVB devices in the Linux kernel now for a pretty long time.  I
> also noticed that it's been marked experimental since inception and
> that nothing seems to use it or have a real example of it for the DVB
> spec (v4lutils' dvb wrappers included).  Is there a grave reason this
> thing is still marked experimental?  It seems in theory like a good
> way to prevent context switches.

There's no grave reason why it is marked as experimental... it is just
that userspace apps don't use it yet, except for dvbv5-zap, when passing
an extra option to enable it.

> I'm nearly considering experimenting with modifying mythtv's DVB
> demuxing, tuning, and streaming routines to use this.  Not because I
> need to, mind you, it's just an ancient system and I'm trying to
> prevent every ounce of the occasional hiccup that happens.
> 
> https://www.kernel.org/doc/html/v5.15/userspace-api/media/dvb/dmx-mmap.html

It would be nice if MythTV and other apps would support MMAP.

If you have time, and want to do that, It sounds great to me.
You could also add support for it on Kaffeine - with already uses
libdvbv5 - so maybe it could be simpler to add support for it too.

Anyway, from my side it sounds welcomed to have userspace apps using
it. Once we have some application using it for a couple Kernel versions,
I guess I could just remove "experimental" from the Kernel drivers.

Thanks,
Mauro