[pulseaudio-discuss] [PATCH] echo-cancel: Avoid segfaults due to invalid master sink or source

[Georg Chini]

On 06.05.2017 22:06, Tanu Kaskinen wrote:
> On Sat, 2017-05-06 at 20:06 +0200, Georg Chini wrote:
>> On 06.05.2017 18:36, Tanu Kaskinen wrote:
>>> On Fri, 2017-05-05 at 16:21 +0200, Georg Chini wrote:
>>>> I agree with you that my patch is wrong, but I think there is a simpler
>>>> solution than your patch. The reason why the move is triggered at all
>>>> is because the virtual sink becomes the default sink when no other
>>>> sink is available. Then a null-sink turns up and the streams are moved
>>>> away from the default sink. This does not make sense anyway for a
>>>> virtual sink, we don't want the streams to move away from there.
>>>> So the simple fix is to prevent the virtual sink from being the default
>>>> sink when it is not connected to a master, then the move will not occur.
>>>> If you are OK with that approach, I would send a patch.
>>> By "the virtual sink", do you mean the null sink? Would you want it to
>>> be impossible to make any null sink the default sink? That doesn't seem
>>> like a good idea, so do you propose some more nuanced policy?
>> No, by virtual sink I mean the filter sink. I think you did not get what I
>> wanted to say. When there is no other sink, the filter sink becomes
>> the default before the null sink turns up. Then streams are moved
>> from the moving filter sink to the new null sink. If we prevent the
>> filter sink from becoming the default while its sink input is moving,
>> the problem will not happen in the first place.
>> I'll send a patch, maybe you understand better what I mean then.
> I made a strange interpretation, because what you really meant seemed
> even more crazy. I forgot that module-switch-on-connect only moves
> streams if they are routed to the default sink, and because of that
> missing piece your explanation made no sense to me at all. I understand
> the logic now.
>
> Implementing your proposal doesn't seem that simple: what if the user
> has set a filter sink as the default sink? Would you change the default
>   sink just for the duration of the filter sink move?
>
I already implemented it and it is quite simple (using part of your
patch).

The default sink will be set to the new sink by switch-on-connect
anyway (even the configured default sink), so the previous user
choice is irrelevant. I think however, that the simple logic of
switch-on-connect should at least be changed so that in the case
that the previous default sink was a filter then the streams should
not be moved away from it (unless the new sink also is a filter).
But this would be a matter of a different patch.

BTW did you see my other remark about switch-on-connect? It is
somewhat hidden in another topic.