linux-kernel - Re: [PATCH 1/3] tcm: Add Thin Provisioning / UNMAP emulation and Block Limits VPD page

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Date:	Wed, 29 Sep 2010 02:05:56 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	Jens Axboe <axboe@...nel.dk>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	Hannes Reinecke <hare@...e.de>,
	James Bottomley <James.Bottomley@...e.de>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Richard Sharpe <realrichardsharpe@...il.com>
Subject: Re: [PATCH 1/3] tcm: Add Thin Provisioning / UNMAP emulation and
	Block Limits VPD page

On Tue, 2010-09-28 at 14:55 -0400, Martin K. Petersen wrote:
> >>>>> "nab" == Nicholas A Bellinger <nab@...ux-iscsi.org> writes:
> 
> nab> This patch also adds the Block Limits VPD (0xb0) page
> 
> You should add the Thin Provisioning VPD page as well and set TPU and/or
> TPWS.
> 

Greetings mkp,

So I was looking at adding this VPD page orginally to set TPU=1 w/ DP=0
(because I don't believe there is currently way to get build the
PROVISIONING GROUP DESCRIPTORs from Block Discard knowledge), but I
ended getting a bit confused by the THRESHOLD EXPONENT, and what value
this should returned for the TCM/IBLOCK and TCM/FILEIO backstores when
blk_queue_discard()==1 is enabled.

Since this is currently not implemented in scsi_debug.c or used in any
way by sd.c AFAICT, do you have any additional information on how this
should be determined together with the UNMAP -> blk_issue_discard()
emulation bits..?

Thanks!

--nab

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