Re: [PATCH] Revert most of 15cc2bb [media] DVB: dtv_property_cache_submit shouldn't modifiy the cache

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 05-11-2011 15:57, Lawrence Rust escreveu:
> On Sat, 2011-11-05 at 18:38 +0100, Andreas Oberritter wrote:
> [snip]
>> I don't get how this could be useful. MythTV knows what delivery system
>> it wants to use, so it should pass this information to the kernel.
>> Trying to set an invalid delivery system must fail.
>>
>> Using SYS_UNDEFINED as a pre-set default is different from setting
>> SYS_UNDEFINED from userspace, which should always generate an error IMO,
>> unless this is documented otherwise in the API specification.
> 
> It's not ideal that MythTV is setting DTV_DELIVERY_SYSTEM to 0 and I
> have filed a bug against this.  But that doesn't change the fact that
> the original patch significantly changed user parameter handling for no
> significant benefit.  MythTV is probably the biggest client of v4l and
> will greatly hinder users upgrading to (Myth)Ubuntu 12.04 or Fedora 16
> both of which use Linux 3.x.

Regression is a bad thing. However, in this specific case, I agree with
Andreas: an assumption that the Kernel will replace SYS_UNDEFINED by something
else is a very bad thing. It also hides a bug, as there are no way for devices 
that support more than one delivery system to properly select the desired
one. 

So, this patch won't fix it.

So, I suspect that you'll need to open a BZ also at Ubuntu and Fedora, in
order to backport the MythTV fix into them.

Regards,
Mauro