linux-kernel - Re: New TRIM/UNMAP tree published (2009-05-02)

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Message-ID: <49FDE50A.4060503@garzik.org>
Date:	Sun, 03 May 2009 14:40:10 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Matthew Wilcox <matthew@....cx>, Jens Axboe <jens.axboe@...cle.com>
CC:	Boaz Harrosh <bharrosh@...asas.com>,
	Hugh Dickins <hugh@...itas.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Mark Lord <lkml@....ca>
Subject: Re: New TRIM/UNMAP tree published (2009-05-02)

Jeff Garzik wrote:
> (2) determine at init if queue (a) supports explicit DISCARD and/or (b) 
> supports DISCARD flag passed with READ or WRITE

As an aside -- does any existing command set support case #b, above?

AFAICT, ATA, SCSI and NVMHCI all have a single, explicit hardware 
command to discard/deallocate unused sectors.

Therefore, creating REQ_TYPE_DISCARD seems to eliminate any need for new 
hook ->prepare_discard().

This provides a 1:1 correspondence between hardware and struct request, 
most closely matching the setup of known hardware.

	Jeff

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