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Subject: Re: [PATCH 1/3] tcm: Add Thin Provisioning / UNMAP emulation and
	Block Limits VPD page
From: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi <linux-scsi@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Douglas Gilbert <dgilbert@interlog.com>, Jens Axboe <axboe@kernel.dk>,
        FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
        Mike Christie <michaelc@cs.wisc.edu>, Hannes Reinecke <hare@suse.de>,
        James Bottomley <James.Bottomley@suse.de>,
        Konrad Rzeszutek Wilk <konrad@darnok.org>,
        Boaz Harrosh <bharrosh@panasas.com>,
        Richard Sharpe <realrichardsharpe@gmail.com>
In-Reply-To: <yq1sk0taeal.fsf@sermon.lab.mkp.net>
References: <1285627889-6450-1-git-send-email-nab@linux-iscsi.org>
	 <yq1sk0taeal.fsf@sermon.lab.mkp.net>
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Date: Wed, 29 Sep 2010 02:05:56 -0700
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On Tue, 2010-09-28 at 14:55 -0400, Martin K. Petersen wrote:
> >>>>> "nab" == Nicholas A Bellinger <nab@linux-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