Re: [9fans] page fault with lock held

[Brantley Coile <brantley@coraid.com>]

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ATA has a common and squalid past.
ATAPI is a packet interface layed on top of ATA to pass
SCSI commands to things like CDROMs, but ATA as such
has it's own protocol.

ATA started out as a chip from Western Digitial, the WD1010.  This
ST506 disk controller was used in XT and AT PC. When the silicon could
support it, the functions were moved into the devices and all that was
left was the interface to the 1010.

Logical block addresses have replaced the cyl, head, sector, but much
of the interface is the same as the one I was programming in 1983.
DMA speeds are faster, things like S.M.A.R.T. allow watching for errors
on drives, and now we even have command queueing, but mostly
it's the same stuff.

I like the idea of having a way to hook into the bottom of sd from user
land!

  Brantley

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From: Dan Cross <cross@math.psu.edu>
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] page fault with lock held
Date: Wed, 13 Apr 2005 09:13:43 -0400
Message-ID: <200504131313.j3DDDhJ16603@augusta.math.psu.edu>

Russ Cox <russcox@gmail.com> writes:
> 
> > I had wanted to see an sdloopback device (devsdloop was I suppose
> > what I called it) that could speak SCSI to a file descriptor that
> > could come from anywhere.  Then things like this might not need to
> > be in the kernel at all.
> 
> sd has little to do with scsi.
> in particular, these devices don't speak scsi.

Maybe I'm confused; it's been a while.  I thought that AoE was ATA over
Ethernet or something like that, and that ATA was basically the SCSI
protocol over different electronics.  I was originally looking at this
in terms of a digital camera that connected via USB, which did speak
SCSI.  Regardless, the salient point was that there should some way to
hook into the devsd framework from userland.

	- Dan C.