Zack's Kernel News

Character Devices in User Space

Tejun Heo has been working on CUSE (character devices in user space), which is similar to FUSE and is based on the same code, with the main differences occurring at initialization. This effort spawned a number of requests for a corresponding BUSE, block devices in user space, but Tejun said applying this technique to block devices wouldn't really produce much of an improvement over loopback mounting and would require much more than the slight modification of FUSE necessary for CUSE. He did admit that loopback over FUSE was problematic and that probably anything would be better than that.

Junjiro R. Okajima said that his own ULOOP driver, which essentially implemented this very thing, already existed. Mike Hommey also suggested DUSE, device mapper in user space, although he followed his own post with a link to the DmUserspace project that did this already. Until now, it seems that CUSE has really been the odd one out.

Tejun announced an OSS (open sound system) proxy that uses CUSE as its back end and is intended as a replacement for the old and largely removed OSS drivers that are currently emulated in ALSA. Tejun explains that the problem with OSS under ALSA is that if the sound card doesn't support multiple audio streams, users must choose whether to use ALSA or OSS at any given moment. With his OSS proxy, which is really an emulation tool, the sound card can support ALSA and OSS simultaneously.

Adrian Bunk pointed out that after six years of effort at replacing all OSS drivers with ALSA, ALSA now supports nearly all applications. He suggested that if Tejun knew of an application that didn't work under it, he should fix the ALSA support rather than writing an OSS emulator. Greg Kroah-Hartman said that even if the OSS implementation was redundant, the underlying CUSE project was still useful for a number of other projects. And Tejun defended his OSS project, saying that at the very least, old binaries were lying around, as well as old code bases that wouldn't work with ALSA and wouldn't be updated. An OSS emulator would let people use those old games and tools.

SR-IOV Support

Yu Zhao coded up support for single-root I/O virtualization (SR-IOV), which allows multiple concurrently running operating systems on a given piece of hardware to share the same PCI device without exploding. SR-IOV is a nice piece of a puzzle that will one day let users do a lot of cool stuff.

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