From: David Sterba <dsterba@suse.cz>
To: Andreas Dilger <adilger@dilger.ca>
Cc: Eric Sandeen <sandeen@sandeen.net>,
Qu Wenruo <quwenruo.btrfs@gmx.com>, Joshi <joshiiitr@gmail.com>,
linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: cross-fs copy support
Date: Tue, 2 Oct 2018 10:15:44 +0200 [thread overview]
Message-ID: <20181002081544.GW3255@twin.jikos.cz> (raw)
In-Reply-To: <FE6394EC-5CB0-4A16-AAC6-97F465A4E50C@dilger.ca>
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:
> > http://man7.org/linux/man-pages/man2/copy_file_range.2.html
>
> There was a patch to allow cross-mount copy for NFS, but it hasn't landed
> yet.
I found https://marc.info/?l=linux-nfs&m=144138779721907&w=2 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.
next prev parent 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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