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From: David Sterba <>
To: Andreas Dilger <>
Cc: Eric Sandeen <>,
	Qu Wenruo <>, Joshi <>,,,,
Subject: Re: cross-fs copy support
Date: Tue, 2 Oct 2018 10:15:44 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, Oct 01, 2018 at 01:51:09PM -0600, Andreas Dilger wrote:
> > Yes, I would expect there to be problems with his modified kernel
> > for a filesystem that supports clone_file_range, because
> > vfs_copy_file_range() will clone if possible, and this should fail across
> > filesystems.
> > 
> > In general, though, I don't know for sure why we don't fall back to
> > do_splice_direct() across filesystems, although the filesystems that
> > implement their own ->copy_file_range ops may have their own,
> > further restrictions within their implementations.
> > 
> > This call /is/ documented in the manpage as only being valid for
> > files on the same filesystem, though:
> >
> There was a patch to allow cross-mount copy for NFS, but it hasn't landed
> yet.

I found that lifts
the VFS check (part of a series that can't be easily linked to).

The lack of cross-mount reflink (based on the copy_file_ragne) is often
confusing users, there are common setups that mount subvolumes
separately and reflinking between them would require mount of the
toplevel subvolume.

If there are 2 in-kernel users of the relaxed cross-mount copy, I think
this would help to push the series forward.

  reply	other threads:[~2018-10-02 14:57 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-01 14:32 cross-fs copy support Joshi
2018-10-01 14:48 ` Qu Wenruo
2018-10-01 15:15   ` Joshi
2018-10-01 15:49   ` Eric Sandeen
2018-10-01 19:51     ` Andreas Dilger
2018-10-02  8:15       ` David Sterba [this message]
2018-10-02 15:19         ` Darrick J. Wong
2018-10-02 18:28       ` J. Bruce Fields

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