IDE - now what? [LWN.net]

As covered on this week's front page, all of Marcin Dalecki's "IDE cleanup" work has been removed from the 2.5.32 kernel and replaced with the 2.4 "foreport." That leaves the IDE code in a state not that far removed from where it was when the 2.5 series started, and the Halloween freeze date is getting closer. What is going to happen to the IDE code now, and who will do it?

At the moment, nobody is stepping forward to be the next IDE maintainer. For the time being it looks like Jens Axboe and Alan Cox are willing to oversee new IDE work and filter it on its way to Linus - but they will not necessarily do a lot of that work themselves. Alan has laid down some conditions, though:

I want order to this. That means all the driver cleanup goes into 2.4-ac (or "2.4-ide" or some suitable branch) first where we can verify we aren't hitting 2.5 generic bugs and ide corruption is a meaningful problem report. It means someone (not me) is the appointed 2.5 person and handles stuff going to 2.5 (I'm happy to identify stuff that tests ok in 2.4 as candidates). It also means random patches not going past me.

If we can do it that way I'll do the job. If Linus applies random IDE "cleanup" patches to his 2.5 tree that don't pass through Jens and me then I'll just stop listening to 2.5 stuff.

In other words, the 2.4-ac tree becomes the development area for new IDE work before it heads into 2.5. And Alan doesn't want to have to contend with patches taking other paths into 2.5. (Alan has also posted the set of attributes an IDE maintainer should have for anybody who is interested in the job).

What is going to happen with the IDE code? A few people have requested that somebody pick up Marcin's work and finish the job, but nobody who is actually working with IDE seems to have much interest in that. Quoting Alan again:

Its easier to go back to functionally correct code and do the job nicely than to fix the 2.5.3x code. Right now I'm working on Andre's current code in 2.4.20pre2-ac* starting off with only provably identical transforms between AndreCode and C and documenting it

So it looks like the 2.4 IDE implementation is here to stay. Or, at least, something based on it - Andre Hedrick, as it turns out, has not been idle during this time. He has a whole set of patches - much of which is already in the -ac series - for nice things like Serial ATA, pluggable low-level transport drivers, modular chipset support, etc. At this point, it's hard to imagine this code not moving into 2.5 once it proves stable.

Linus has his own plans for the future of the IDE code. These plans involve making some relatively minor changes to the current IDE core, mostly around moving some functionality up toward the block layer. Once that's done, development on a new "IDE-TNG" driver would begin. The existing IDE code at that point would be mostly frozen and thus remain stable; new work would happen in the new, scary, dangerous "TNG" driver. Support for older hardware would be removed from the TNG driver, allowing a great deal of historical cruft to be cleaned out.

In retrospect, creating a new version of the IDE subsystem was the obvious way to carry out a major reworking of this code. You simply can not have a fundamental layer like IDE be unstable for months and expect to get a lot of other work done. The previous IDE transition (from the old "hd" driver) was handled in this manner. Had Marcin's work been done this way, he might well still be at it now.

As it is, the window of opportunity for major IDE work in 2.5 has closed. There is time for smaller cleanups and the addition of needed features, but nobody has any appetite for anything that would seriously destabilize IDE again this close to the freeze date.

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