Date: Sat, 5 Oct 2024 21:11:26 +0300 From: Christos Margiolis <christos@freebsd.org> To: Alfonso Sabato Siciliano <alfix86@gmail.com> Cc: multimedia@freebsd.org Subject: Re: New meaning oss_sysinfo.nummixers Message-ID: <phsdnmvoyjlxyrqr73djj4id3znciifyygvt6tr7racrw3ruq7@xq4gex3jmts3> In-Reply-To: <CAPJrGM0-ptpwZg8nB1MMJhbUr2tMuTG=Tnagce8UXQJjp2nDyw@mail.gmail.com>
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Hello Alfonso,
Alfonso Sabato Siciliano wrote:
> I was inactive for months, one week ago I reinstalled CURRENT on my main
> laptop (and others). The meaning of "struct oss_sysinfo.nummixers"
> changed. Let's say:
>
> [...]
>
> Output "nummixers: 7", But
>
> % sysctl dev.pcm
> ... prints 6 devices dev.pcm.[0-5].*
>
> % ls /dev/mixer*
> /dev/mixer0 /dev/mixer1 /dev/mixer2 /dev/mixer3 /dev/mixer4 /dev/mixer5
>
> 6 mixers from 0 to 5. But now oss_sysinfo.nummixers is 7, it was 6 until
> some months ago.
>
> I thought the new value could be the max index, in the case some mixers
> are closed, example /dev/mixer0 /dev/mixer2 /dev/mixer5. But in this
> case 'nummixers' should be 5 not 7.
>
> Maybe the hidden /dev/mixer is in the count (6 + 1 = 7).
>
> Same situation on 3 laptops. So, what is the new meaning for
> oss_sysinfo.nummixers?
The behavior changed in the following commit of mine: 5d980fadf73d
("sound: Handle unavailable devices in various OSS IOCTLs") [1].
The commit message explains the rationale behind changing this
behavior. I am aware it's a bit quite unintuitive, but it solves quite a
few bugs we have with people using nummixers to loop through mixer
devices, which I suppose is the most typical use.
oss_sysinfo.nummixers now is simply populated with whatever
devclass_get_maxunit(pcm_devclass) returns, which should be the _next_
maximum unit number that will be allocated for an audio device, hence
the 7 you get (this is how devclass_get_maxunit() works in general).
Although a bit tedious, you can count the actual number of mixers in the
system by issuing open(2) for each /dev/mixer<n> and seeing which ones
succeed. This way you know the total number, but also which mixers
specifically are present.
Christos
[1] https://cgit.freebsd.org/src/commit/?id=5d980fadf73df64a1e0eda40a93170ed76ce6f14
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