From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jens Axboe <axboe@suse.de>
Subject: Re: PATCH: exclude certain commands from emulated SCSI hosts
Date: Mon, 24 Mar 2003 17:52:30 +0100
Sender: linux-scsi-owner@vger.kernel.org
Message-ID: <20030324165230.GS2371@suse.de>
References: <1048519237.1982.16.camel@mulgrave> <Pine.LNX.4.44.0303240827030.3010-100000@home.transmeta.com>
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To: Linus Torvalds <torvalds@transmeta.com>
Cc: James Bottomley <James.Bottomley@SteelEye.com>, Matthew Dharm <mdharm-scsi@one-eyed-alien.net>, USB Developers <linux-usb-devel@lists.sourceforge.net>, USB Storage List <usb-storage@one-eyed-alien.net>, Linux SCSI list <linux-scsi@vger.kernel.org>

On Mon, Mar 24 2003, Linus Torvalds wrote:
> 
> On 24 Mar 2003, James Bottomley wrote:
> > > 
> > > For disk-like media:
> > > 
> > > READ_10
> > > WRITE_10
> > 
> > We do about the best we can for read and write.  For sd, we gauge the
> > size of the command from the size of the medium:  <1Gb=> six byte, from
> > 1Gb to 2Tb 10 byte, over 2Tb 16 byte, so I think this should all be
> > fine.
> 
> Really? The code was _supposed_ to always start off with READ/WRITE_10's,
> and then fall back to the old READ/WRITE_6 if it gets errors from that. Do 
> we really have some broken random-number generator semantic still in teh 
> SCSI layer? That sounds like a piece of crock.

It's not true, ->ten is set unconditionally and we only fall back to 6
byte cdb's if we see an ILLEGAL_REQUEST on a READ_10/WRITE_10.

So the logic is, always assume 10-byte commands. If an incoming request
cannot be addressed with 10-byte commands, use 16.

-- 
Jens Axboe