linux-kernel - Re: [PATCH v5 4/5] block: loop: prepare for supporing direct IO

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Date:	Mon, 22 Jun 2015 20:19:27 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Tejun Heo <tj@...nel.org>, Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v5 4/5] block: loop: prepare for supporing direct IO

On Wed, Jun 10, 2015 at 3:40 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Tue, Jun 09, 2015 at 09:49:25PM +0800, Ming Lei wrote:
>> This patches provides two approaches for enabling direct IO
>> from user space:
>>
>>       - userspace(such as losetup) can pass 'file' which is
>>       opened/fcntl as O_DIRECT
>>       - sysfs file is provided to run dio tests easily
>
> I really don't think two interfaces are a good idea here.  The interface
> for loop has always been that userspaces passes a FD and we use it,
> so let's keep it that way.

That makes sense.

>
> And while we're at it please also send a patch for losetup so that we
> can actually use the feature.

I have wrote 2 patches to enable direct-io for backing file in util-linux,
and they can be found in below tree:

http://kernel.ubuntu.com/git/ming/util-linux.git/log/?h=losetup-dio

I will post them in util-linux mail list later.

thanks
Ming
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