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Message-ID: <47169E12.2080108@tmr.com>
Date: Wed, 17 Oct 2007 19:43:14 -0400
From: Bill Davidsen <davidsen@....com>
To: Jeff Garzik <jeff@...zik.org>
CC: Greg KH <greg@...ah.com>, Rob Landley <rob@...dley.net>,
James Bottomley <James.Bottomley@...eleye.com>,
Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
linux-scsi@...r.kernel.org, Jens Axboe <axboe@...e.de>,
Suparna Bhattacharya <suparna@...ibm.com>,
Nick Piggin <piggin@...erone.com.au>
Subject: Re: What still uses the block layer?
Jeff Garzik wrote:
>> But again, please remember that these USB devices are really SCSI
>> devices. Same for SATA devices. There is a reason they are using the
>> SCSI layer, and it isn't just because the developers felt like it :)
>
> /somewhat/ true I'm afraid: libata uses the SCSI layer for ATAPI
> devices because they are essentially bridges to SCSI devices. It uses
> the SCSI layer for ATA devices because the SCSI layer provided a huge
> amount of infrastructure that would need to have been otherwise
> duplicated, /then/ massaged into coordinating between <jgarzik's ATA
> layer> and <SCSI layer> when dealing with ATAPI.
>
> There is also a detail that was of /huge/ value when introducing a new
> device class: distro installers automatically work, if you use SCSI. If
> you use a new block device type, that behaves differently from other
> types and is on a different major, you have to poke the distros into
> action or do it yourself.
>
> IOW, it was the high Just Works(tm) value of the SCSI layer when it came
> to ATA (not ATAPI) devices.
>
> For the future, ATA will eventually be more independent (though the SCSI
> simulator will be available as an option, for compat), but the value is
> big enough to put that task on the back-burner.
>
I remember being told that I didn't understand the problem when I
suggested using ide-scsi for everything and just hiding the transport. I
get great pleasure from having been (mostly) right on that one. I still
have old systems running ZIP drives as scsi...
--
Bill Davidsen <davidsen@....com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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