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

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Date:	Thu, 29 Jan 2015 11:02:58 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-api@...r.kernel.org, Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [RESEND] [PATCH] block: create ioctl to discard-or-zeroout a range of blocks

On Wednesday 28 January 2015 18:00:25 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.
> 
> This patch depends on "block: Add discard flag to
> blkdev_issue_zeroout() function" in Jens' for-3.20/core branch.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> 

Would this work ok for devices that fill discarded areas with all-ones
instead of all-zeroes? I believe SD cards can do either.

	Arnd
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