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Date:   Wed, 2 Mar 2022 19:50:01 -0500
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Josef Bacik <josef@toxicpanda.com>
Cc:     linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nfs@vger.kernel.org, Chuck Lever <chuck.lever@oracle.com>
Subject: Re: nfs generic/373 failure after "fs: allow cross-vfsmount
 reflink/dedupe"
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On Wed, Mar 02, 2022 at 07:29:34PM -0500, Josef Bacik wrote:
> On Wed, Mar 02, 2022 at 07:07:35PM -0500, J. Bruce Fields wrote:
> > Sorry, took me a minute to understand, myself:
> > 
> > It's actually only the client behavior that changed.  Previously the
> > client would reject an attempt to clone across filesystems, so the
> > server never saw such a request.  After this patch, the client will go
> > ahead and send the CLONE.  (Which, come to think of it, is probably the
> > right thing for the client to do.)
> > 
> > So the server's probably always had a bug, and this just uncovered it.
> > 
> > I'd be curious what the consequences are.  And where the check should be
> > (above or below vfs_clone_file_range()?).
> > 
> 
> This is where I'm confused, this really shouldn't succeed
> 
> loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
>                            struct file *file_out, loff_t pos_out,
>                            loff_t len, unsigned int remap_flags)
> {
>         loff_t ret;
> 
>         WARN_ON_ONCE(remap_flags & REMAP_FILE_DEDUP);
> 
>         if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
>                 return -EXDEV;
> 
> 
> loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
>                             struct file *file_out, loff_t pos_out,
>                             loff_t len, unsigned int remap_flags)
> {
>         loff_t ret;
> 
>         file_start_write(file_out);
>         ret = do_clone_file_range(file_in, pos_in, file_out, pos_out, len,
>                                   remap_flags);
> 
> And even if we get past here, I imagine XFS would freak out because it can't
> find the extents (unless you're getting lucky and everything is lining up?).
> I'm super confused...

Bah, I see what you mean.  Maybe there's something wrong with my setup.
I'll try some more stuff and report back....

--b.