linux-kernel - Re: [PATCH 6/9] target: Allow sbc_ops->execute_rw() to accept SGLs + data

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Message-ID: <20130821063524.GH25506@infradead.org>
Date:	Tue, 20 Aug 2013 23:35:24 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Nicholas A. Bellinger" <nab@...erainc.com>
Cc:	target-devel <target-devel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	Martin Petersen <martin.petersen@...cle.com>,
	Chris Mason <chris.mason@...ionio.com>,
	James Bottomley <JBottomley@...allels.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: Re: [PATCH 6/9] target: Allow sbc_ops->execute_rw() to accept SGLs +
 data_direction

On Tue, Aug 20, 2013 at 08:07:57PM +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@...erainc.com>
> 
> COMPARE_AND_WRITE expects to be able to send down a DMA_FROM_DEVICE
> to obtain the necessary READ payload for comparision against the
> first half of the WRITE payload containing the verify user data.
> 
> Currently virtual backends expect to internally reference SGLs,
> SGL nents, and data_direction, so change IBLOCK, FILEIO and RD
> sbc_ops->execute_rw() to accept this values as function parameters.
> 
> Also add the sbc_execute_rw() wrapper to handle the special case
> for the initial COMPARE_AND_WRITE DMA_FROM_DEVICE -> READ I/O
> submission.

I don't like the way this is structured with the new method.  It seems
like we should just pass the sgl and associated data to execute_cmd
and have the read vs write logic driven by command code, using generic
flags instead of specificly checking for compare and write.

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