From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Becker Subject: Re: [LSF/MM TOPIC][ATTEND] protection information and userspace Date: Thu, 7 Feb 2013 01:40:14 -0800 Message-ID: <20130207094012.GA28047@localhost> References: <20130206195122.GA30652@sgi.com> <20130206202444.GA4771@blackbox.djwong.org> <20DAFDEA-0C44-478E-B406-C5B08BC67FBC@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Darrick J. Wong" , Ben Myers , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, martin.petersen@oracle.com To: Chuck Lever Return-path: Received: from zeniv.linux.org.uk ([195.92.253.2]:49854 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757118Ab3BGJkW (ORCPT ); Thu, 7 Feb 2013 04:40:22 -0500 Content-Disposition: inline In-Reply-To: <20DAFDEA-0C44-478E-B406-C5B08BC67FBC@oracle.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Feb 06, 2013 at 03:34:49PM -0500, Chuck Lever wrote: > > On Feb 6, 2013, at 3:24 PM, "Darrick J. Wong" wrote: > > > 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. > > I'm writing a requirements document for the NFS protocol which I can discuss at LSF. The use cases for NFS for now would be virtual disk devices (hypervisors) or direct NFS access to storage from user space. > > Like everyone else we are waiting for a magical VFS and user space API to appear that can pass PI to and from storage. I'm happy to chat about it. Unfortunately, like Darrick says, sys_dio() coding hasn't happened. I do think we're better off with some kind of explicit API than some magic state on the file. I mean, even something like: ssize_t write_with_pi(int fd, const void *buf, size_t count, const void *pi, size_t pi_count); It's not as nice as a non-historical API (eg sys_dio), but it also probably plays nicer with buffered I/O. Joel > > > 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. > > > > > > > > --D > >> > >> Regards, > >> Ben > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > >> the body of a message to majordomo@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Chuck Lever > chuck[dot]lever[at]oracle[dot]com > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- "I think it would be a good idea." - Mahatma Ghandi, when asked what he thought of Western civilization http://www.jlbec.org/ jlbec@evilplan.org