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

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Date:	Thu, 15 Nov 2012 11:29:46 -0800
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH 3/3] target/iblock: Add WRITE_SAME w/ UNMAP=0 emulation
 support

On Thu, 2012-11-15 at 06:04 -0500, Christoph Hellwig wrote:
> > +	/*
> > +	 * Enable WRITE_SAME emulation for IBLOCK, use scsi_debug.c default
> > +	 */
> 
> Why would we care what scsi_debug.c uses?
> 

Fixing up this comment based upon MKP's earlier response.

> > +	dev->dev_attrib.max_write_same_len = 0xFFFF;
> >  
> >  	if (blk_queue_nonrot(q))
> >  		dev->dev_attrib.is_nonrot = 1;
> > @@ -375,22 +379,80 @@ err:
> >  	return ret;
> >  }
> 
> > +static struct bio *iblock_get_bio(struct se_cmd *, sector_t, u32);
> > +static void iblock_submit_bios(struct bio_list *, int);
> > +static void iblock_complete_cmd(struct se_cmd *);
> 
> I'd suggest moving the write_same callback below these to avoid
> forward declarations.
> 

Will take care of this in a separate patch..

> > +	if (cmd->se_cmd_flags & SCF_WRITE_SAME_DISCARD) {
> 
> I'd probably add separate write_same and write_same_unmap members to
> the sbc_ops structure.  That'll keep decoding which one is used in the
> SBC code, and it'll keep the implementations nicely separated.
> 

Done.

> > +	if (sectors > cmd->se_dev->dev_attrib.max_write_same_len) {
> 
> This sort of check should stay in the SBC code.
> 

Fixing this up now.

> > +	sg = &cmd->t_data_sg[0];
> 
> Btw, it seems like we don't bother to ensure the S/G list length
> is just one sector for WRITE SAME with either the unmap bit set or not.
> 

Well at least for the latter that is because UNMAP=0 does not have a
payload.  ;)

Adding a check to ensure that we have one SGL, and that SGL length
matches sector_size for UNMAP=0 logic.

> Also please add testcases for WRITE SAME including corner cases like
> incorrect transfer length to the scsi testsuite to ensure this code
> has proper QA coverage.

<nod>

--nab

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