Re: [PATCH 03/11] vfs: no fallback for ->copy_file_range

Dave Chinner
2018-12-03T23:02:39Z

On Mon, Dec 03, 2018 at 12:22:21PM +0200, Amir Goldstein wrote:
> On Mon, Dec 3, 2018 at 10:34 AM Dave Chinner <david@fromorbit.com> wrote:
> >
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > Now that we have generic_copy_file_range(), remove it as a fallback
> > case when offloads fail. This puts the responsibility for executing
> > fallbacks on the filesystems that implement ->copy_file_range and
> > allows us to add operational validity checks to
> > generic_copy_file_range().
> >
> > Rework vfs_copy_file_range() to call a new do_copy_file_range()
> > helper to exceute the copying callout, and move calls to
> > generic_file_copy_range() into filesystem methods where they
> > currently return failures.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
>
> You may add
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
>
> After fixing the overlayfs issue below.
> ...
>
> > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> > index 84dd957efa24..68736e5d6a56 100644
> > --- a/fs/overlayfs/file.c
> > +++ b/fs/overlayfs/file.c
> > @@ -486,8 +486,15 @@ static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
> > struct file *file_out, loff_t pos_out,
> > size_t len, unsigned int flags)
> > {
> > - return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
> > + ssize_t ret;
> > +
> > + ret = ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
> > OVL_COPY);
> > +
> > + if (ret == -EOPNOTSUPP)
> > + ret = generic_copy_file_range(file_in, pos_in, file_out,
> > + pos_out, len, flags);
> > + return ret;
> > }
> >
>
> This is unneeded, because ovl_copyfile(OVL_COPY) is implemented
> by calling vfs_copy_file_range() (on the underlying files) and it is
> not possible
> to get EOPNOTSUPP from vfs_copy_file_range().

Except that it is possible. e.g. If the underlying filesystem tries
a copy offload, gets a "not supported" failure from the remote
server and then doesn't implement a fallback.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com