On Thu, Feb 18, 2021 at 7:33 AM Olga Kornievskaia [off-list ref] wrote:

On Wed, Feb 17, 2021 at 3:30 PM Luis Henriques [off-list ref] wrote:

quoted

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@chromium.org/ (local)
Link: https://lore.kernel.org/linux-fsdevel/CANMq1KDZuxir2LM5jOTm0xx+BnvW=ZmpsG47CyHFJwnw7zSX6Q@mail.gmail.com/ (local)
Link: https://lore.kernel.org/linux-fsdevel/20210126135012.1.If45b7cdc3ff707bc1efa17f5366057d60603c45f@changeid/ (local)
Reported-by: Nicolas Boichat <redacted>
Signed-off-by: Luis Henriques <redacted>
---
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.