linux-kernel - Re: [PATCH] block: Don't allow illegal discard requests

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Date:	Wed, 4 Nov 2015 15:17:15 +0100
From:	Jan Kara <jack@...e.cz>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.com>, axboe@...nel.dk,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] block: Don't allow illegal discard requests

On Wed 04-11-15 03:30:19, Christoph Hellwig wrote:
> On Wed, Nov 04, 2015 at 10:18:41AM +0100, Jan Kara wrote:
> > Currently blkdev_issue_discard() doesn't check that submitted discard
> > request matches granularity required by the underlying device.
> > Submitting such requests to the device can have unexpected consequences
> > (e.g. brd driver just discards more / less data depending on how exactly
> > the request is aligned). So test that submitted discard request has the
> > granularity required by the driver.
> 
> How is this going to work with stacked drivers?  I think brd needs to
> be fixed to take care of the granularity itself, just like we did for
> request based drivers.

So you mean that a stacked driver would split a discard request so that it
is no longer of the required granularity? OK, makes sense. I'll add the
check directly into brd itself.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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