On Wed, Feb 06, 2013 at 03:34:49PM -0500, Chuck Lever wrote:
>
> On Feb 6, 2013, at 3:24 PM, "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> 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.
> >
> > <end rambling>
> >
> > --D
> >>
> >> Regards,
> >> Ben
> >> --
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>
> --
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
>
>
>
>
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