linux-kernel - Re: [PATCH 0/9] target: Add support for COMPARE_AND

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Date:	Tue, 20 Aug 2013 14:53:08 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Christoph Hellwig <hch@....de>
Cc:	"Nicholas A. Bellinger" <nab@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>,
	Martin Petersen <martin.petersen@...cle.com>,
	Chris Mason <chris.mason@...ionio.com>,
	James Bottomley <JBottomley@...allels.com>
Subject: Re: [PATCH 0/9] target: Add support for COMPARE_AND_WRITE (VAAI)
 emulation

On Tue, 2013-08-20 at 23:29 +0200, Christoph Hellwig wrote:
> On Tue, Aug 20, 2013 at 08:07:51PM +0000, Nicholas A. Bellinger wrote:
> > 
> > It's also currently lacking the necessary sychronization between I/O
> > submission of COMPARE_AND_WRITE verify instance and write instance
> > user data, which is still being worked on in order to avoid additional
> > overhead in the main I/O fast path.
> 
> I don't think merging such a non-conforming implementation makes any sense.
> 

Yes, I don't intend to merge anything that's not fully functional.

The idea was to get review going on these pieces first.  I'll be posting
an PATCH-v2 to complete the implementation over the next days.

> Also for a complex command like this with all it's race potential I would
> really like to see some test cases to go along with it.
> 

Yes, Eric @ PureStorage has a sg_compare_write that I'm using to test
this.  It's probably about time that this be included in upstream
sg3-utils too..

--nab

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