[alsa-devel] [PATCH] pcm: route: Don't handle no matching chmap as a serious error

David Henningsson david.henningsson at canonical.com
Wed Mar 19 13:10:55 CET 2014

On 03/19/2014 10:57 AM, Takashi Iwai wrote:
> At Tue, 18 Mar 2014 23:13:02 +0100,
> David Henningsson wrote:
>> On 03/18/2014 05:34 PM, Takashi Iwai wrote:
>>> At Tue, 18 Mar 2014 17:19:29 +0100,
>>> David Henningsson wrote:
>>>> On 03/18/2014 03:27 PM, Takashi Iwai wrote:
>>>>> When find_matching_chmap() returns an error for the non-matching
>>>>> chmap, the caller, snd_pcm_route_open(), also returns an error
>>>>> although it shouldn't be handled as the fatal error.  This results in
>>>>> the probe error with PulseAudio and it gives no real output in the
>>>>> end.
>>>> Hmm, could you give a more specific example? In case the driver does not
>>>> support channel maps at all, that case is handled in the beginning of
>>>> the function.
>>> Well, the problem is that PulseAudio doesn't work at all with the
>>> current alsa-lib git prior to the commit in some cases.  That is, the
>>> commit brought some incompatibility.
>> Hmm, then the error should be somewhere in determine_chmap instead.
>> tt_chmap should be NULL (i e, find_matching_chmap is never called) for
>> using the standard number syntax instead of the new chmap syntax.
>> What about the patch attached instead (untested) ?
>>>> So this only happens if the driver supports channel maps, but only
>>>> non-compatible with the requested map. In which case I believe it's
>>>> correct that the probing should fail...?
>>> Could you check whether PA 5.0 works as is with alsa-lib git (before
>>> the last fix)?  It could be seen on some desktop machines.
>> Let me know if the attached patch works for you. In case it does not I
>> will do this testing later.
> It seems working, but it revealed another bug, too.  I fixed it in git
> tree, and reverted my last patch along with it.

I don't think the patch "route: Fix invalid pointer access" is necessary
because determine_chmap is always called before any usage of tt_chmap,
and the function always assigns a value to tt_chmap. But it does not
hurt either, of course.

Thanks for the testing!

David Henningsson, Canonical Ltd.

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