linux-kernel - Re: [PATCH] block: correctly fallback for zeroout

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Message-ID: <yq1lh2nrnei.fsf@sermon.lab.mkp.net>
Date:	Thu, 02 Jun 2016 22:56:05 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
Cc:	Shaohua Li <shli@...com>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, snitzer@...hat.com, axboe@...com,
	martin.petersen@...cle.com, Kernel-team@...com
Subject: Re: [PATCH] block: correctly fallback for zeroout

>>>>> "Sitsofe" == Sitsofe Wheeler <sitsofe@...oo.com> writes:

Sitsofe> The original SCSI WRITE SAME has overloaded semantics - not
Sitsofe> only does it mean "write this data multiple times" but it can
Sitsofe> also be used to mean "discard this range" too. If the kernel's
Sitsofe> command was modelled on the SCSI original perhaps this
Sitsofe> conflation clouded things?

REQ_WRITE_SAME in the context of the kernel explicitly means "write
payload to this block range".

A REQ_DISCARD command may be serviced using WRITE SAME(16) with the
UNMAP bit set in the SCSI disk driver but that's entirely orthogonal.

-- 
Martin K. Petersen	Oracle Linux Engineering