Re: [PATCH v2 01/10] VFS generic copy_file_range() support

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

On Sat, Dec 1, 2018 at 10:12 PM Olga Kornievskaia
<olga.kornievskaia@gmail.com> wrote:
>
> On Sat, Dec 1, 2018 at 5:00 PM Dave Chinner <david@fromorbit.com> wrote:
> >
> > On Sat, Dec 01, 2018 at 10:11:48AM +0200, Amir Goldstein wrote:
> > > On Fri, Nov 30, 2018 at 10:04 PM Olga Kornievskaia
> > > <olga.kornievskaia@gmail.com> wrote:
> > > >
> > > > Relax the condition that input files must be from the same
> > > > file systems.
> > > >
> > > > Add checks that input parameters adhere semantics.
> > > >
> > > > If no copy_file_range() support is found, then do generic
> > > > checks for the unsupported page cache ranges, LFS, limits,
> > > > and clear setuid/setgid if not running as root before calling
> > > > do_splice_direct(). Update atime,ctime,mtime afterwards.
> > > >
> > > > Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> > > > ---
> > >
> > > This patch is either going to bring you down or make you stronger ;-)
> > >
> > > This is not how its done. Behavior change and refactoring mixed into
> > > one patch is wrong for several reasons. And when you relax same sb
> > > check you need to restrict it inside filesystems, like your previous patch
> > > did.
> > .....
> > > In any case, I hear that Dave is neck deep in fixing copy_file_range()
> > > so changes to this function should be collaborated with him. Or better
> > > yet, wait until he posts his fixes and carry on from there.
> >
> > Yeah, because I've heard nothing for a month and this is kinda
> > important
>
> Dave I think that's unfair. It is important. NFS is actually the file
> system that needed VFS support for cross fs copy_file_range and I was
> working on it. If you were in doubt, you could have emailed and asked
> me.

Just to be clear. What I think was unfair in that comment was the
wording "this is kinda important". I think a lot stems from lack of
clarity in the the mailing list communications. I object to the fact
that it wasn't clear who was going to implement the functionality.
Since the work was needed by NFS I didn't want to assume that somebody
in VFS would just do it for us. At the time nobody in VFS stood up and
said they would do the work and thus I tried to do my best.

I'm grateful, and would have been in the first place, that somebody
did support generic cross-filesystem functionality. Thus I'm by no
means speaking against Dave's work.

> I'm unsure now what does this mean. I have a patch series with a VFS
> patch that went thru the extensive review (people spend time on it)
> and an NFS patch series that depends on it that is ready for the
> upstream push. Are you saying that the VFS patch is no longer welcomed
> and thus NFS series is no longer viable either?

I'm unclear of the fate of the patch set that has the (v7) VFS patch
that was reviewed and approved and is thought to be pushed for 4.21.
It is unclear if the new work is on top of that or not.

> , I have a series of 8-9 patches that make all the fixes we
> > need, push the cross-filesystem checks down into the filesystems,
> > and let filesystems handle the fallback to a splice based copy
> > themselves (because there are way more fallback cases than just
> > EOPNOPSUPP and EXDEV).
>
> Are you saying it is each individual filesystem responsibility to
> fallback on splice? Isn't that a step backwards? Each individual
> filesystem is going to implement the same code of calling
> do_splice_direct() to do the functionally that could and should be in
> VFS?
>
> >
> > I also have a patch for the man page that document all the missing
> > failure cases, and document where things are filesystem specific or
> > not.
> >
> > And I also have a fstests patch that exercises all the failure cases
> > so that all filesystems will end up behaving the same way for all
> > the same cases they should.
> >
> > I'm still sorting out the fstests patch (it requires changes
> > to xfs_io's copy-range command) so I've got some confidence that the
> > code actually does what it says in the man page, but I should have
> > that sorted in a couple of days.
> >
> > Cheers,
> >
> > Dave.
> >
> > --
> > Dave Chinner
> > david@fromorbit.com