Subject: oss compatibility for >2 channels
To: None <>
From: Matthias Drochner <>
List: tech-misc
Date: 04/25/2007 00:44:22
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Hi -
that's neither kern nor purely userlevel -- maybe that list
is still good for something.

PR pkg/35444 (mplayer bad timeout select and play.channels number for oss)
reminds me of something: The NetBSD OSS emulation assumes that the number
of play and record channels is the same. It seems common now that there is
some 5.1 audio output but just a one or two channel input.
The emulated SNDCTL_DSP_CHANNELS ioctl tries to set both play and record
channels to the given number and fails if any of it fails. So there is no
chance to enable more than two channels in that example.

I'd suggest to treat play and record direction independently - see the
appended patch. Is there anyone having deeper knowledge about OSS,
or being able to test a real OSS with >2 channel hardware to judge
whether such a change makes sense?

best regards

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# old_revision [5fff99846d67879b2e498b71d01a3761adaef1c6]
# patch "lib/libossaudio/ossaudio.c"
#  from [ccf71c78ccaf56ea3a45ba9d0aad1782acf7d753]
#    to [d3cb57b84f77a93c843aa96b3f8a7b423e1b9361]
--- lib/libossaudio/ossaudio.c	ccf71c78ccaf56ea3a45ba9d0aad1782acf7d753
+++ lib/libossaudio/ossaudio.c	d3cb57b84f77a93c843aa96b3f8a7b423e1b9361
@@ -240,7 +240,9 @@ audio_ioctl(int fd, unsigned long com, v
- =
+		(void) ioctl(fd, AUDIO_SETINFO, &tmpinfo);
+		AUDIO_INITINFO(&tmpinfo);
 		tmpinfo.record.channels = INTARG;
 		(void) ioctl(fd, AUDIO_SETINFO, &tmpinfo);
 		/* FALLTHRU */