X-Git-Url: https://git.ralfj.de/osspd.git/blobdiff_plain/1ba9230bb0f360046a7a9dd7c94e451556d57727..HEAD:/README diff --git a/README b/README index 6b716c7..a56aa1b 100644 --- a/README +++ b/README @@ -1,119 +1 @@ - - OSS Proxy - emulate OSS device using CUSE - - Copyright (C) 2008-2009 SUSE Linux Products GmbH - Copyright (C) 2008-2009 Tejun Heo - -1. What is it? --------------- - -Well, first, OSS refers to Open Sound System. If it still doesn't -ring a bell, think /dev/dsp, /dev/adsp and /dev/mixer. - -Currently, Linux supports two audio programming interface - ALSA and -OSS. The latter one is deprecated and has been that way for a long -time but there still are applications which still use them including -UML (usermode Linux) host sound support. - -ALSA contains OSS emulation but sadly the emulation is behind -multiplexing layer (which is in userland) which means that if your -sound card doesn't support multiple audio streams, only either one of -ALSA or OSS interface would be usable at any given moment. - -There have been also attempts to emulate OSS in userland using dynamic -library preloading - aoss and more recently padsp. This works for -many applications but it's just not easy to emulate everything using -the technique. Things like polling, signals, forking, privilege -changes make it very difficult to emulate things reliably. - -OSS Proxy uses CUSE (extension of FUSE allowing character devices to -be implemented in userspace) to implement OSS interface - /dev/dsp, -/dev/adsp and /dev/mixer. From the POV of the applications, these -devices are proper character devices and behave exactly the same way -so it can be made quite versatile. - - -2. Hmmm... So, how does the whole thing work? ---------------------------------------------- - -The OSS Proxy daemon - osspd - should be started first. Note that -osspd will fail to start if sound device number regions are already -occupied. You'll need to turn off OSS or its emulation[1]. - -On startup, osspd creates /dev/dsp, /dev/adsp and /dev/mixer using -CUSE. When an application access one of the devices, all IOs are -redirected to osspd via CUSE. Upon receiving a new DSP open request, -osspd creates a slave process which drops the root privilege and -assumes the opening process's credentials. After handshaking, osspd -forwards all relevant IOs to the slave which is responsible for -actually playing the sound. - -Currently there's only one slave implemented - ossp-padsp, which as -the name suggests forwards (again) the sound to pulseaudio. To sum -up, the whole pipe looks like the following. - - App <-> /dev/dsp <-> CUSE <-> osspd <-> ossp-padsp <-> pulseaudio - -Which is a lot of forwarding, but on modern machines, it won't be too -noticeable. - - -3. What works? --------------- - -Well, MIDI part isn't implemented and I doubt it will be in any near -future but except that everything should work. Playing, recording, -5.1ch, A-V syncing, all should work. If not, it's a bug, so please -report. - -The mixer behaves a bit differently tho. In the original OSS, -/dev/mixer is the hardware mixer, so adjusting volumes there affects -all audio streams. When using ossp, each process group gets its own -mixer and the mixer always contains only two knobs - PCM and IGAIN. -Combined with per-stream volume control of pulseaudio, this scheme -works quite well for applications with embedded volume control -although it makes standalone OSS mixer programs virtually useless[2]. - - -4. How do I use it? -------------------- - -First you need CUSE support in kernel which might land on 2.6.28 with -sufficient luck[3] and then you also need libfuse which supports -CUSE[4]. Once you have both, it should be easy. First build it by -running `make'. You can set OSSPD_CFLAGS, OSSPD_LDFLAGS, -OSSP_PADSP_CFLAGS and OSSP_PADSP_LDFLAGS if you have stuff at -non-default locations. - -After build completes, there will be two executables - `osspd' and -`ossp-padsp'. Just copy them to where other system executables live. -Specific location doesn't matter as long as both files end up in the -same directory. - -Execute `osspd'. It will create the device files and you're all set. -`osspd' uses syslog with LOG_DAEMON facility, so if something doesn't -work take a look at what osspd complains about. - - -[1] As of this writing, turning on any sound support makes the - soundcore module claim OSS device regions. Patch to make it claim - OSS device regions only when OSS support or emulation is enabled - is scheduled for 2.6.28. Even with the patch, soundcore will - claim OSS device regions if OSS support or ALSA OSS emulation is - enabled. Make sure they're turned off. - -[2] If you have a strong reason to use standalone OSS mixer program, - you can play some shell tricks to put it into the same process - group as the target audio application. e.g. To use aumix with - mpg123 - `(mpg123 asdf.mp3 > /dev/null 2>&1 & aumix)', but - seriously, just use PA or ALSA one. - -[3] For the time being, here's the git tree with all the necessary - changes. This tree is base on top of 2.6.27-rc3. - - http://git.kernel.org/?p=linux/kernel/git/tj/misc.git;a=shortlog;h=cuse - git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git cuse - -[4] And libfuse with the modifications can be found at... - - http://userweb.kernel.org/~tj/ossp/fuse-cuse.tar.gz +This repository moved to https://salsa.debian.org/debian/osspd