Re: "Enhanced" MD code avaible for review

From: Jeff Garzik
Date: Tue Mar 30 2004 - 16:49:45 EST

Justin T. Gibbs wrote:
That's unfortunate for those using ATA. A command submitted from userland

Required, since one cannot know the data phase of vendor-specific commands.

So you are saying that this presents an unrecoverable situation?

No, I'm saying that the data phase need not have a bunch of in-kernel checks, it should be generated correctly from the source.

Particularly, checking whether the kernel is doing something wrong, or wrong,
just wastes cycles. That's not a scalable way to code... if every driver
and Linux subsystem did that, things would be unbearable slow.

Hmm. I've never had someone tell me that my SCSI drivers are slow.

This would be noticed in the CPU utilization area. Your drivers are probably a long way from being CPU-bound.

I don't think that your statement is true in the general case. My
belief is that validation should occur where it is cheap and efficient
to do so. More expensive checks should be pushed into diagnostic code
that is disabled by default, but the code *should be there*. In any event,
for RAID meta-data, we're talking about code that is *not* in the common
or time critical path of the kernel. A few dozen lines of validation code
there has almost no impact on the size of the kernel and yields huge
benefits for debugging and maintaining the code. This is even more
the case in Linux the end user is often your test lab.

It doesn't scale terribly well, because the checks themselves become a source of bugs.


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