linux-kernel - Re: [PATCH 3/3] target/iblock: Add WRITE

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Date:	Mon, 19 Nov 2012 12:38:18 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Elliott, Robert (Server Storage)" <Elliott@...com>
CC:	Christoph Hellwig <hch@....de>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Christoph Hellwig <hch@...radead.org>,
	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH 3/3] target/iblock: Add WRITE_SAME w/ UNMAP=0 emulation
 support

Il 15/11/2012 21:01, Elliott, Robert (Server Storage) ha scritto:
> WRITE SAME always has a payload, regardless of the UNMAP bit value.
> 
> For WRITE SAME with UNMAP=0, it's extremely important; that's how
> what to write is specified.
> 
> For WRITE SAME with UNMAP=1, the device server is required to check
> that the payload matches the data that is returned for unmapped LBAs.
> lf LBPRZ=1 (read zeros for unmapped LBAs), that means checking that
> the payload has all zeros.  In sbc3r33, this rule is tucked away in
> model section 4.7.3.4.3, not the command section 5.41.

Does that mean that LBPRZ=0, LPBWS=1 is practically an invalid
combination?  Because there's no real way for the device server to
perform the check successfully.

Paolo

> I would like to change that rule (it's a nuisance and a performance
> burden), but that's the current rule going into SBC-3 letter ballot.
> 
> Changing WRITE SAME with UNMAP=1 to ignore the payload would provide
> essentially the same functionality as changing the UNMAP command to
> be mandatory, not just a hint; both approaches have been discussed.
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