[dm-devel] Re: "Enhanced" MD code avaible for review

[Jeff Garzik]

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.

	Jeff