Re: [LSF/MM TOPIC][ATTEND] protection information and userspace

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Ben Myers <bpm@sgi.com>
Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
	linux-scsi@vger.kernel.org, martin.petersen@oracle.com
Subject: Re: [LSF/MM TOPIC][ATTEND] protection information and userspace
Date: Wed, 6 Feb 2013 12:24:44 -0800	[thread overview]
Message-ID: <20130206202444.GA4771@blackbox.djwong.org> (raw)
In-Reply-To: <20130206195122.GA30652@sgi.com>

On Wed, Feb 06, 2013 at 01:51:22PM -0600, Ben Myers wrote:
> Hi,
> 
> I'm interested in discussing how to pass protection information to and from
> userspace.  Maybe Martin could be enlisted for the discussion.
> 
> I read that some work has already been done in this area but have not been able
> to locate it.  It looks like the bio-integrity code already makes it possible
> to generate the t10-dif crc in the filesystem.  It would be good to be able to
> get the guard and application tags back out to backup applications such as
> xfsdump.  Enabling other applications to generate their own tags in userspace
> is also interesting.

This one's been on my list for a couple of years (and companies) too.  A few
years ago Joel Becker had support for it in his sys_dio proposal (that hasn't
gone anywhere), and more recently I've theorized that we could add a magic
fcntl/ioctl to make the kernel recognize, say, the first iovec of a O_DIRECT
*{read,write}v call as the PI buffer, which I think is similar to how DIX gets
PI data to a disk.  But it's not like I have any code to show for it.

I /think/ it's fairly straightforward to change the directio submit code to
find the userspace PI buffer and amend the block integrity code to attach our
own PI buffer.  You'd still have to let the block layer set the sector # field,
but afaik that won't affect the crc or the app tag.

I hear that the NFS guys want to propose some sort of protocol for transmitting
PI data (across NFS), but I haven't seen anything concrete yet.

Well, I hope I'll scrape together the time to hack together a PoC before LSF...
on the other hand, I ran the discussion about PI userland interfaces at LPC2011
and (shamefully) haven't done anything yet.

<end rambling>

--D
> 
> Regards,
> 	Ben
> --
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