[7990] in linux-scsi channel archive
Re: Devices not supporting read-6....
daemon@ATHENA.MIT.EDU (Drew Eckhardt)
Wed Feb 2 15:50:59 2000
Message-Id: <200002022025.NAA20336@chopper.poohsticks.org>
To: "Kenneth D. Merry" <ken@kdm.org>
Cc: Jonas Nickel <jonas.nickel@tu-berlin.de>,
Rogier Wolff <R.E.Wolff@BitWizard.nl>, linux-kernel@vger.rutgers.edu,
linux-scsi@vger.rutgers.edu, phoenix@thesindicate.com
In-reply-to: Your message of "Wed, 02 Feb 2000 01:02:04 MST."
<20000202010204.A40068@panzer.kdm.org>
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Content-ID: <20333.949523149.1@chopper.Poohsticks.ORG>
Date: Wed, 02 Feb 2000 13:25:49 -0700
From: Drew Eckhardt <drew@Poohsticks.Org>
In message <20000202010204.A40068@panzer.kdm.org>, ken@kdm.org writes:
>On Tue, Feb 01, 2000 at 22:40:26 -0700, Drew Eckhardt wrote:
>> In the SCSI-1 spec that some of this conformed to, Read-6 was required.
>> Read-10 was suggested as a good idea. Since some devices Wedged until
>> power cycled when fed a command they didn't support, I figured that
>> using Read-6 until we absolutely positively had to use Read-10 was a
>> fine idea.
>FWIW, even in the SCSI-1 spec, 10-byte reads were mandatory for CDROM and
>WORM devices, and 6-byte reads were optional. (It is that way in the
>SCSI-2 spec, and I think in the MMC specs as well.)
I worked off the X3T9.2 REV 17B draft.
It covers Direct Access devices, Sequential Access devices, and Printers.
In each section, there are tables of 6 and 10 byte supported commands. In
the Direct Access section we have the following:
Key: M = Command implementation is mandatory.
E = Command implementation is required for SCSI devices that support
device-independent self-configuring software.
Table 8-1
Group 0 Commands for Direct-Access Devices
==============================================================================
Operation
Code Type Command Name Section
------------------------------------------------------------------------------
08H M READ 8.1.4
Table 8-22
Group 1 Commands for Direct-Access Devices
28H E READ 8.2.2
>The way we handle this in FreeBSD is to specify a minimum command size in
>the function that builds read and write CCBs.
Under Linux, the CD and disk drivers are completely divorced. When I
wrote the disk driver, I used the smallest command possible for a given
transfer size. The CD driver was cloned from that.
They should probably share a common direct-access support file that
does that.
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