2.5 IDE considered harmful [LWN.net]

The volume of the complaints about the 2.5 IDE subsystem is increasing. Consider this posting from Russell King:

If stuff in 2.5 wasn't soo broken (looking at IDE here) then more people would be using it, and less people would be wanting the 2.5 features back ported to 2.4. IMHO, at the moment 2.5 has a major problem. It is not getting the testing it deserves because things like IDE and such like aren't reasonably stable enough.

...or this one from Andi Kleen...

Testing 2.5 (in this case with x86-64) is a major problem unless you're lucky enough to find a SCSI adapter and a SCSI disk. IDE just deadlocks and hangs too often. This prevents testing everything else and stops development in 2.5 for many things.

The state of the IDE code is seen by many as a drag on the 2.5 development process as a whole. For those who are concerned, there are a few things worth looking at.

Part of the problem, apparently, is that the 2.5.25 kernel is missing several of the more recent patches, which fix serious problems. As Martin Dalecki puts it:

My plan is to provide a 98 soon which will be cummulative against 2.5.25, just to geive people a chance to work on it again. But as it stands - *plain* 2.5.25 is indeed very dangerous in this regard.

Martin's IDE-98 patch has not been posted as of this writing; those wanting to run 2.5.25 on an IDE system in the mean time and actually keep their files should apply this set of patches.

Interestingly, most of those patches were not posted by Martin (who has been on vacation). Instead, the recent IDE patches have been produced by Bartlomiej Zolnierkiewicz. Bartlomiej seems to take a bit more cautious approach, and even has the respect of former IDE maintainer Andre Hedrick. With luck, he will be more involved in future IDE work. Few people contest the need to "clean up" the IDE layer, but this work needs to be done in a very careful way.

Meanwhile, a different approach has been taken by Jens Axboe. It is normal for interesting features in the current development series to be backported to the previous stable kernel. Thus, for example, Alan Cox's 2.4.19-ac patch includes the O(1) scheduler from 2.5. Jens has gone the other direction and posted a patch (since updated) which "foreports" the 2.4 IDE layer to 2.5. His purpose was to have a stable platform to work on; the patch will be maintained until the 2.5 IDE layer becomes a little more trustworthy. It is not intended to be a long-term replacement for that layer.

With luck, the 2.5 IDE issues will settle out soon. Meanwhile, caution (or a SCSI system) is suggested for people running 2.5.

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