GIF>I8DD@E> Kernel News Q8:BËJB

9ki=JXjXC`eloÈE\ok>\e\iXk`feÉ=`c\jpjk\d Chris Mason has migrated BtrFS devel- put in a prominent position as soon as term solution for NGFS, and (c) because opment onto its own git repository possible so as to attract a body of con- creating a new enterprise filesystem al- and is starting to lean toward submitting tributors. ways takes longer than people expect, the code into the main kernel tree. Sev- Adrian Bunk is skeptical of that the- and even then, it takes a while for enter- eral technical problems, not least of ory, citing ext4 as an example of a file- prise users to trust a new filesystem for which is that the on-disk format hasn’t system that was accepted early into the their most critical data, ext4 in the next stabilized yet, are standing in the way kernel and did not experience the accel- generation of filesystems was needed as of this. erated development for which Andrew the bridge to the NGFS.” Without a stable format, users will was hoping. Serge E. Hallyn objected He added, “It is fair to say that BtrFS have to be informed clearly that the ear- and said that because BtrFS is really isn’t just a private project of a single lier formats will not be supported after a cool, having it available in mainline Linux kernel developer, but rather the certain time. And there will always be would have a special excitement factor design has been discussed and reviewed those users who didn’t get the memo that ext4 lacked. But Adrian pointed out by a large number of experienced filesys- and are therefore out of luck when they that anyone could install BtrFS without tem architects.” need to access their data later. Chris’s it being in the mainline tree. It does seem clear that unless some- plan is to get as close as possible to a The discussion went back and forth, thing weird happens, BtrFS will be in a final disk format and to include back- and at some point Theodore (Ted) T’so kernel near you quite soon. ward compatibility on any changes made piped up with his take on the politics. after that. If successful, the effect on Essentially, he said, Adrian was op- C`elo=fle[Xk`feK89 users would be much less severe. posed to early merging, whereas Andrew ext2, ext3, ext4, OCFS2, Lustre, abreast of the latest discussions and de- Wireless USB (WUSB), and WiMedia cisions, selected and summarized by BtrFS, AdvFS, ReiserFS, and XFS – came LLC Protocol (WLP) subsystems, felt Zack. Zack has been publishing a weekly together for a two-day ‘next generation that the code was ready to be included online digest, the Kernel Traffic news- filesystem’ (NGFS) workshop. in the mainline tree, and he created a letter for over five years now. Even “At the end of the workshop, there git repository from which folks can pull. reading Kernel Traffic alone can be a was unaminous agreement (including Without much discussion, some folks time consuming task. from yours truly) that (a) Linux needed were a little unclear as to whether David Linux Magazine now provides you with a next-generation filesystem to be com- was submitting his code for inclusion or the quintessence of Linux Kernel activi- petitive, (b) Chris Mason’s BtrFS (with just for review. Barring any big technical ties, straight from the horse’s mouth. some changes/ enhancements discussed issue, it does seems as though the code during the workshop) was the best long- will be accepted soon.

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072-073_kernel.indd 72 16.10.2008 15:54:08 Uhr Kernel News GIF>I8DD@E>

:_XiXZk\i;\m`Z\j`eLj\iJgXZ\ Tejun Heo has been working on CUSE DmUserspace project that did this al- ALSA support rather than writing an OSS (character devices in user space), which ready. Until now, it seems that CUSE has emulator. Greg Kroah-Hartman said that is similar to FUSE and is based on the really been the odd one out. even if the OSS implementation was re- same code, with the main differences Tejun announced an OSS (open sound dundant, the underlying CUSE project occurring at initialization. This effort system) proxy that uses CUSE as its back was still useful for a number of other spawned a number of requests for a cor- end and is intended as a replacement for projects. And Tejun defended his OSS responding BUSE, block devices in user the old and largely removed OSS drivers project, saying that at the very least, old space, but Tejun said applying this tech- that are currently emulated in ALSA. binaries were lying around, as well as nique to block devices wouldn’t really Tejun explains that the problem with old code bases that wouldn’t work with produce much of an improvement over OSS under ALSA is that if the sound card ALSA and wouldn’t be updated. An OSS loopback mounting and would require doesn’t support multiple audio streams, emulator would let people use those old much more than the slight modification users must choose whether to use ALSA games and tools. of FUSE necessary for CUSE. He did or OSS at any given moment. With his admit that loopback over FUSE was OSS proxy, which is really an emulation JI$@FMJlggfik problematic and that probably anything tool, the sound card can support ALSA Yu Zhao coded up support for single-root would be better than that. and OSS simultaneously. I/O virtualization (SR-IOV), which al- Junjiro R. Okajima said that his own Adrian Bunk pointed out that after six lows multiple concurrently running op- ULOOP driver, which essentially imple- years of effort at replacing all OSS driv- erating systems on a given piece of hard- mented this very thing, already existed. ers with ALSA, ALSA now supports ware to share the same PCI device with- Mike Hommey also suggested DUSE, de- nearly all applications. He suggested that out exploding. SR-IOV is a nice piece of a vice mapper in user space, although he if Tejun knew of an application that puzzle that will one day let users do a lot followed his own post with a link to the didn’t work under it, he should fix the of cool stuff.

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