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

From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.com>,
	axboe@kernel.dk, LKML <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] block: Don't allow illegal discard requests
Date: Wed, 4 Nov 2015 15:17:15 +0100	[thread overview]
Message-ID: <20151104141715.GB10124@quack.suse.cz> (raw)
In-Reply-To: <20151104113019.GA24128@infradead.org>

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@suse.com>
SUSE Labs, CR