"Btrfs v0.16 is available for download," began Chris Mason, announcing the latest release of his new Btrfs filesystem. He noted, "v0.16 has a shiny new disk format, and is not compatible with filesystems created by older Btrfs releases. But, it should be the fastest Btrfs yet, with a wide variety of scalability fixes and new features." Improved scalability and performance improvements include fine grained btree locking, pushing CPU intensive operations such as checksumming into their own background threads, improved data=ordered mode, and a new cache to reduce IO requirements when cleaning up old transactions. Other new features include support for ACLs, prevention of orphaned inodes so files won't be lost after a crash, and a more robust directory index format. Chris noted:

"There are still more disk format changes planned, but we're making every effort to get them out of the way as quickly as we can. You can see the major features we have planned on the development timeline. [...] the btrfs kernel module now weighs in at 30,000 LOC, which means we're getting very close to the size of ext[34]."

"The big advantage Hammer has over Tux3 is, it is up and running and released in the Dragonfly distro," began Daniel Phillips, offering a comparison between the two filesystem. He continued, "the biggest disadvantage is, it runs on BSD, not Linux, and it so heavily implements functionality that is provided by the VFS and block layer in Linux that a port would be far from trivial. It will likely happen eventually, but probably in about the same timeframe that we can get Tux3 up and stable." This led into a lengthy and interesting technical discussion between Daniel and HAMMER author Matthew Dillon, comparing the design of the two filesystems.

Matthew reviewed the Tux3 notes and replied, "it sounds like Tux3 is using many similar ideas [as HAMMER]. I think you are on the right track. I will add one big note of caution, drawing from my experience implementing HAMMER, because I think you are going to hit a lot of the same issues. I spent 9 months designing HAMMER and 9 months implementing it. During the course of implementing it I wound up throwing away probably 80% of the original design outright." Daniel noted that he's been working on the Tux3 design for around ten years, "and working seriously on the simplifying elements for the last three years or so, either entirely on paper or in related work like ddsnap and LVM3." Matthew cautioned, "I can tell you've been thinking about Tux for a long time. If I had one worry about your proposed implementation it would be in the area of algorithmic complexity. You have to deal with the in-memory cache, the log, the B-Tree, plus secondary indexing for snapshotted elements and a ton of special cases all over the place. Your general lookup code is going to be very, very complex. My original design for HAMMER was a lot more complex (if you can believe it!) then the end result. A good chunk of what I had to do going from concept to reality was deflate a lot of that complexity." The friendly conversation offers a very detailed look at the design choices made in each of these file systems.

"So it's been a week since -rc1, and -rc2 is out there," began Linux creator Linus Torvalds, announcing the 2.6.27-rc2 Linux kernel. He noted, "there's a lot of random changes in there, and I'm hoping we're starting to calm down, but one particular _kind_ of random change is probably worth pointing out explicitly due to the things it can result in: the fact that a number of architectures ended up using the 'lull' after -rc1 (hah!) to do the 'include/asm-xyz' => 'arch/xyz/include/asm' renames." Linus explained that for people actively developing and merging code with git, "be aware that we've recently had more renames than the rename detection limit in git defaults to, and as a result, if you have a rename<->data change conflict, you may want to increase the default limit." Linus noted that developers with sufficient ram can set "renamelimit=0" to completely disable the limit, and others can set it to a high value such as 5,000, "the default limit is pretty low just to not cause problems for people who have less memory in their machines than kernel developers tend to have..."

Linus continued, "the dirstat (with rename detection on, so as to not show the movement as huge changes) is fairly usual, with most of the changes in drivers, along with an ext4 and xfs update making 'fs' show up pretty high too". He added:

"The shortlog is still a tad too big to make it on the list (again, as usual - normally I end up posting shortlogs for -rc3 and later when they become more manageable) but let me just say that it isn't really all that interesting. Theres' a lot of small changes here, but nothing that makes you go 'Wow!'. Not that there _should_ be anything like that in -rc2, of course, so I'm not complaining."

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"I have had to apply the reiser4 patches from -mm kernels to vanilla based patchset for over a year now. Reiser4 works fine, what will it take to get it included in vanilla?" began a brief thread on the Linux Kernel mailing list. Theodore Ts'o offered several links detailing the reamining issues with Reiser4, then suggested, "people who really like reiser4 might want to take a look at btrfs; it has a number of the same design ideas that reiser3/4 had --- except (a) the filesystem format has support for some advanced features that are designed to leapfrog ZFS, (b) the maintainer is not a crazy man and works well with other LKML developers (free hint: if your code needs to be reviewed to get in, and reviewers are scarce; don't insult and abuse the volunteer reviewers as Hans did --- Not a good plan!)."

Edward Shishkin noted that Reiser4 development continues, "I am working on the plugin design document. It will be ready approximately in September. I believe that it'll address all the mentioned complaints." He added, "This document [defines] plugins [and] primitives (like conversion of run-time objects) used in reiser4, and describes all reiser4 interfaces, so that it will be clear that VFS functionality is not duplicated, there are not VFS layers inside reiser4, etc."

Hans Reiser, the original developer of the Reiser4 filesystem, was convicted of first degree murder on April 28'th, 2008. The latest Reiser4 patches currently live on kernel.org, as do the necessary support programs.

"I do think 'next' as it is has a few issues that either need to be fixed (unlikely - it's not the point of next) or just need to be aired as issues and understood," noted Linus Torvalds about the linux-next development tree, originally designed as a way to get subsystem maintainers more involved in managing merge conflicts. Linus continued, "I don't think anybody wants it to go away. The question in my mind is more along the way of how/whether it should be changed. There was some bickering about patches that weren't there, and some about how _partial_ series were there but then the finishing touches broke things."

He listed his two primary concerns as, "I don't think it does 'quality control', and I think that's pretty fundamental," and, "I don't think the 'next' thing works as well for the occasional developer that just has a few patches pending as it works for subsystem maintainers that are used to it." Linus continued, "I don't think either of the above issues is a 'problem' - I just think they should be acknowledged. I think 'next' is a good way for the big subsystem developers to be able to see problems early, but I really hope that nobody will _ever_ see next as a 'that's the way into Linus' tree', because for the above two reasons I do not think it can really work that way." Andrew Morton noted, "a lot of the bugs which hit your tree would have been quickly found in linux-next too," then added, "but it's all shuffling deckchairs, really. Are we actually merging better code as a reasult of all of this? Are we being more careful and reviewing better and testing better? Don't think so."

"It's two weeks (and one day), and the merge window is over," began Linus Torvalds, announcing the 2.6.27-rc1 kernel. He continued, "finally. I don't know why, but this one really did feel pretty dang busy. And the size of the -rc1 patch bears that out - at 12MB, it's about 50% bigger than 26-rc1 (but not that much bigger than 24/25-rc1, so it's not like it's anything unheard of)." He reflected, "the pure size of the -rc's _is_ making me a bit nervous, though. Sure, it means that we are good at merging it all, but I have to say that I sometimes wonder if we don't merge too much in one go, and even our current (fairly short) release cycle is actually too big." As for the actual changes, Linus explained:

"Much of -rc1 was in linux-next, but certainly not everything. We'll see how that whole thing ends up evolving - it certainly didn't solve all problems, and there was some bickering about things that weren't there (and some things that mostly were ;), but maybe it helped. There's a ton of new stuff in there, but at least personally the interesting things are the BKL pushdown and perhaps the introduction of the lockless get_user_pages_fast(). The build system also got updated to allow moving the architecture include files ('include/asm-xyz') into the architecture subdirectories ('arch/xyz/include/asm'), and sparc seems to have taken advantage of that already."

Other changes Linus highlighted included merging the UBI filesystem, as well as, "tracing, firmware loading, continued x86 arch merging, and moving more code to generic support (unified generic IPI handling, coherent dma memory allocation, show_mem etc). Bootmem rewrites. [And] some support for further scalability (ie 4k cpu cores)."

"Since everybody seems to be having fun building new filesystems these days, I thought I should join the party, began Daniel Phillips, announcing the Tux3 versioning filesystem. He continued, "Tux3 is a write anywhere, atomic commit, btree based versioning filesystem. As part of this work, the venerable HTree design used in Ext3 and Lustre is getting a rev to better support NFS and possibly become more efficient." Daniel explained:

"The main purpose of Tux3 is to embody my new ideas on storage data versioning. The secondary goal is to provide a more efficient snapshotting and replication method for the Zumastor NAS project, and a tertiary goal is to be better than ZFS."

In his announcement email, Daniel noted that implementation work is underway, "much of the work consists of cutting and pasting bits of code I have developed over the years, for example, bits of HTree and ddsnap. The immediate goal is to produce a working prototype that cuts a lot of corners, for example block pointers instead of extents, allocation bitmap instead of free extent tree, linear search instead of indexed, and no atomic commit at all. Just enough to prove out the versioning algorithms and develop new user interfaces for version control."