In the debate following Andrew Morton [interview] posting his plans for 2.6.13 [story], the existence of a plugin layer in Reiser4 was discussed. Jeff Garzik put it blunty, "the plugin stuff is crap. This is not a filesystem but a filesystem new layer. IMO considered in that light, it duplicates functionality elsewhere." Andrew Morton went on to explain, "I think the concern here is that this is implemented at the wrong level. In Linux, a filesystem is some dumb thing which implements address_space_operations, filesystem_operations, etc."
Hans Reiser noted, "please remember that this is per file, per item, per node, per attribute, per disk format, per bitmap, per super block, etc., abstracting, not per filesystem abstracting." He explained a couple advantages to plugins being that it makes it much easier for developers to change the disk format, and allows for easy code reuse. He added, "the use of plugins forced all the programmers to think about reusability at every layer of design. V3 of reiserfs is way too hard to work on and modify. If you ask one of the team to code something for V3 instead of V4, they quietly groan at the thought. It is just so much easier to do in V4."
Andrew Morton replied, "advanced features such as those which you describe are implemented on top of the filesystem, not within it. reiser4 turns it all upside down. Now, some of the features which you envision are not amenable to above-the-fs implementations. But some will be, and that's where we should implement those." The lengthy discussion continued, an interesting read for Reiser4 supporters and detractors alike.
A recent lkml thread explored an interesting tangent when Jeff Garzik asked about what was to follow the 2.5 development kernel, "is it definitely to be named 2.6? Maybe it's just my impression from development speed, but it felt more like a 3.0 to me :)". Linux creator Linus Torvalds first suggested that there was no reason to skip from 2.5 to 3.0, qualifying it with, "But hey, it's just a number. I don't feel that strongly either way."
Ingo Molnar reflected on the significant improvements we've seen to the VM and the IO subsystem, going so far as to say, "I think due to these improvements if we dont call the next kernel 3.0 then probably no Linux kernel in the future will deserve a major number. In 2-4 years we'll only jump to 3.0 because there's no better number available after 2.8."
Linus agreed that if the VM is as good as it seems to be, indeed the upcoming release deserves to be called 3.0. But he also pointed out that there are many silent users who tend not to speak up until there is an official release. He asks, "people who are having VM trouble with the current 2.5.x series, please _complain_, and tell what your workload is. Don't sit silent and make us think we're good to go.. And if Ingo is right, I'll do the 3.0.x thing."