Re: [PATCH v3] vfs: fix copy_file_range regression in cross-fs copies

[Olga Kornievskaia]

On Thu, Feb 18, 2021 at 1:48 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Thu, Feb 18, 2021 at 7:33 AM Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
> >
> > On Wed, Feb 17, 2021 at 3:30 PM Luis Henriques <lhenriques@xxxxxxx> wrote:
> > >
> > > A regression has been reported by Nicolas Boichat, found while using the
> > > copy_file_range syscall to copy a tracefs file.  Before commit
> > > 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices") the
> > > kernel would return -EXDEV to userspace when trying to copy a file across
> > > different filesystems.  After this commit, the syscall doesn't fail anymore
> > > and instead returns zero (zero bytes copied), as this file's content is
> > > generated on-the-fly and thus reports a size of zero.
> > >
> > > This patch restores some cross-filesystems copy restrictions that existed
> > > prior to commit 5dae222a5ff0 ("vfs: allow copy_file_range to copy across
> > > devices").  It also introduces a flag (COPY_FILE_SPLICE) that can be used
> > > by filesystems calling directly into the vfs copy_file_range to override
> > > these restrictions.  Right now, only NFS needs to set this flag.
> > >
> > > Fixes: 5dae222a5ff0 ("vfs: allow copy_file_range to copy across devices")
> > > Link: https://lore.kernel.org/linux-fsdevel/20210212044405.4120619-1-drinkcat@xxxxxxxxxxxx/
> > > Link: https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@xxxxxxxxxxxxxx/
> > > Link: https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/
> > > Reported-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> > > Signed-off-by: Luis Henriques <lhenriques@xxxxxxx>
> > > ---
> > > Ok, I've tried to address all the issues and comments.  Hopefully this v3
> > > is a bit closer to the final fix.
> > >
> > > Changes since v2
> > > - do all the required checks earlier, in generic_copy_file_checks(),
> > >   adding new checks for ->remap_file_range
> > > - new COPY_FILE_SPLICE flag
> > > - don't remove filesystem's fallback to generic_copy_file_range()
> > > - updated commit changelog (and subject)
> > > Changes since v1 (after Amir review)
> > > - restored do_copy_file_range() helper
> > > - return -EOPNOTSUPP if fs doesn't implement CFR
> > > - updated commit description
> >
> > In my testing, this patch breaks NFS server-to-server copy file.
>
> Hi Olga,
>
> Can you please provide more details on the failed tests.
>
> Does it fail on the client between two nfs mounts or does it fail
> on the server? If the latter, between which two filesystems on the server?
>

It was a pilot error. V3 worked. I'm having some other issues with
server to server copy code but they seem to be unrelated to this. I
will test the new v6 versions when it comes out.

> Thanks,
> Amir.