linux-kernel - Re: [PATCH v4] block: create ioctl to discard-or-zeroout a range of blocks

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Message-ID: <20151208052830.GC10584@birch.djwong.org>
Date:	Mon, 7 Dec 2015 21:28:30 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <axboe@...nel.dk>,
	"Seymour, Shane M" <shane.seymour@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: Re: [PATCH v4] block: create ioctl to discard-or-zeroout a range of
 blocks

On Mon, Dec 07, 2015 at 06:40:15PM -0800, Christoph Hellwig wrote:
> On Fri, Nov 13, 2015 at 02:01:43PM -0800, Darrick J. Wong wrote:
> > Create a new ioctl to expose the block layer's newfound ability to
> > issue either a zeroing discard, a WRITE SAME with a zero page, or a
> > regular write with the zero page.  This BLKZEROOUT2 ioctl takes
> > {start, length, flags} as parameters.  So far, the only flag available
> > is to enable the zeroing discard part -- without it, the call invokes
> > the old BLKZEROOUT behavior.  start and length have the same meaning
> > as in BLKZEROOUT.
> > 
> > Furthermore, because BLKZEROOUT2 issues commands directly to the
> > storage device, we must invalidate the page cache (as a regular
> > O_DIRECT write would do) to avoid returning stale cache contents at a
> > later time.
> 
> So does BLKZEROOUT.  Seems like adding the cache invalidation should
> be one patch and the ioctl another one.  Otherwise this looks fine
> except that I kinda hate BLKZEROOUT2 name, but can't come up with
> anything better.

I should've sent the 4.4 version -- since the ioctl code was refactored into
separate functions and the new function modifies its arguments, I ended up
rewriting most of the function body just to set up the page cache invalidation.

(Ah, I see -- 4.4-rc1 came out and I forgot to resend.)

Blergh, v5 on its way...

--D

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