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

[Amir Goldstein]

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?

Thanks,
Amir.