Re: [PATCH 14/25] vfs: make remap_file_range functions take and return bytes completed

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Oct 10, 2018 at 09:28:34PM +0300, Amir Goldstein wrote:
> On Wed, Oct 10, 2018 at 6:51 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> >
> > On Wed, Oct 10, 2018 at 09:47:00AM +0300, Amir Goldstein wrote:
> > > On Wed, Oct 10, 2018 at 3:14 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> > > >
> > > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > >
> > > > Change the remap_file_range functions to take a number of bytes to
> > > > operate upon and return the number of bytes they operated on.  This is a
> > > > requirement for allowing fs implementations to return short clone/dedupe
> > > > results to the user, which will enable us to obey resource limits in a
> > > > graceful manner.
> > > >
> > > > A subsequent patch will enable copy_file_range to signal to the
> > > > ->clone_file_range implementation that it can handle a short length,
> > > > which will be returned in the function's return value.  Neither clone
> > > > ioctl can take advantage of this, alas.
> > > >
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > ---
> [...]
> > > Commit message wasn't clear enough on the behavior of copy_file_range()
> > > before and after the patch IMO. Maybe it would be better to pospone this
> > > semantic change to the RFR_SHORTEN patch and keep if (cloned == len)
> > > in this patch?
> >
> > There shouldn't be any behavior change here -- all implementations
> > return a negative error code or the length that was passed in.  I'll
> > clarify that in the commit message.
> >
> 
> OK. BTW, you forgot to update Documentation/filesystems/vfs.txt.

Yeah, I noticed that and updated it too.

> Also since this series has a potential to break clone/dedup on
> overlayfs, it would be great if you could run some of the clone/dedupe
> xfstests with overlay over xfs.
> 
> For the simple case of running ./check with a local.config file that is
> not multi section, this just means running ./check -overlay after the
> first ./check run (-overlay doesn't mkfs the base fs).

I'll give it a try, though we should probably both run '-g clone' just
to make sure everything is working...

> If this is a problem, let me know once new devel branch is ready

Yeah, Dave asked me to merge the xfs for-next branch so I'm working on
that too.

> and I'll pull it for testing. If I need to pull in extra xfstests, please
> mention that as well.

You'll probably want "generic: test creation time recovery after power
failure" that I sent to the fstests lists a few days ago.

--D

> 
> Thanks,
> Amir.