Re: [PATCH v1 02/11] VFS permit cross device vfs_copy_file_range

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

On Thu, Oct 25, 2018 at 12:59 AM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Wed, Oct 24, 2018 at 10:59 PM Olga Kornievskaia
> <olga.kornievskaia@gmail.com> wrote:
> >
> [...]
> > It feels like folks are now ok with either the check being in the
> > drivers or doing the check in the VFS layer.
> >
> > I'm picking the choice of not doing the check in the VFS layer because
> > it allows for do_splice_direct() by any caller.
>
> I'm sorry, but this reasoning in flawed and this is not the reason that
> Matthew promoted not doing same fs type check in vfs.

I stated the reason why I picked to do the check at the driver layer.
Looking at your version of the sb type check to be only applied to the
copy_file_range indeed makes my argument invalid. I was under the
impression that sb type check was being proposed as a standalone check
(just like the sb check was standalone). Thus, yes I didn't completely
understand what you proposed.

> You did not understand the option that I was promoting to begin with.
> What I suggested was:
>
> 1. Remove current same sb check in beginning of vfs_copy_file_range()
> 2. Check sb && ->clone_file_range
> 3. Check same sb type && ->copy_file_range
> 4. Cross fs do_splice_direct()
>
> It's fine that you chose not to check for same fs type in VFS before calling
> copy_file_range() method, but still requires an ACK from Al that he agrees
> with passing in file * of another filesystem on the interface.

Al, can you please provide a final decision as to which way you would
prefer for this to be done.

> > I'm about to submit
> > the new version of the patches (this time I will include the NFS patch
> > series). We can continue with the discussion on the new version.
> >
> > I have added checks for the CIFS and OverlayFS to be consistent with
> > the previous behavior -- no cross-device copy_offload, I assume if and
> > when those file systems are ready to make use of it they'll remove the
> > check.
> >
>
> Actually overlayfs code is "ready" for cross sb copy, but neither nfs nor
> cifs are supported as upper file system, so it doesn't matter much.

So then the commit statement is still true. When overlayfs will have
upper file systems that do support it, this check can be removed.

>
> Thanks,
> Amir.