linux-kernel - Re: [PATCH][SCS] sd: Read Capacity if (16) fails

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Message-Id: <1218040543.7493.10.camel@localhost.localdomain>
Date:	Wed, 06 Aug 2008 09:35:43 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Hugh Dickins <hugh@...itas.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][SCS] sd: Read Capacity if (16) fails

On Wed, 2008-08-06 at 08:25 -0600, Matthew Wilcox wrote:
> On Wed, Aug 06, 2008 at 03:06:21PM +0100, Hugh Dickins wrote:
> > Commit e0597d70012c82e16ee152270a55d89d8bf66693 (sd: Identify DIF protection
> > type and application tag ownership) says that if a disk is formatted with
> > Inquiry bit PROTECT=1, it is required to support Read Capacity(16).  But my
> > SD cards, accessed by builtin cardreader and generic USB storage, disagree.
> > 
> > Therefore fall back to the familiar Read Capacity if Read Capacity(16) fails:
> > without even showing the "failed" message since I expect this will be common.
> 
> How about we flip it around?  Unconditionally try READ CAPACITY 16 first,
> then if that fails, try READ CAPACITY?  I suppose there's always the
> possibility that a drive will go tits-up if it receives the RC16
> command, so maybe we'll need a blacklist.

I don't think so ... the read capacity logic looks the way it does
because we had a bit of trouble with USB devices simply going out to
lunch on READ_CAPACITY(16) ... otherwise we'd have done the 16 then
fallback to 10 ages ago.

The best way is probably a blacklist for protect ... I assume there's no
plans in the near future for USB to support it, so we could just turn it
off globally in USB slave configure.

James


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