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From:   Filipe Manana <fdmanana@gmail.com>
Date:   Fri, 29 Nov 2019 12:43:17 +0000
Message-ID: <CAL3q7H76DDdvwoMGcxBTbrHNCKN-qAAnKFN5GtmAyAZvjZkHtw@mail.gmail.com>
Subject: Re: Question about clone_range() metadata stability
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
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On Wed, Nov 27, 2019 at 8:24 PM Darrick J. Wong <darrick.wong@oracle.com> w=
rote:
>
> On Wed, Nov 27, 2019 at 06:38:46PM +0000, Trond Myklebust wrote:
> > Hi all
> >
> > A quick question about clone_range() and guarantees around metadata
> > stability.
> >
> > Are users required to call fsync/fsync_range() after calling
> > clone_range() in order to guarantee that the cloned range metadata is
> > persisted?
>
> Yes.
>
> > I'm assuming that it is required in order to guarantee that
> > data is persisted.
>
> Data and metadata.  XFS and ocfs2's reflink implementations will flush
> the page cache before starting the remap, but they both require fsync to
> force the log/journal to disk.
>
> (AFAICT the same reasoning applies to btrfs, but don't trust my word for
> it.)

Yep, exactly the same for btrfs.


>
> > I'm asking because knfsd currently just does a call to
> > vfs_clone_file_range() when parsing a NFSv4.2 CLONE operation. It does
> > not call fsync()/fsync_range() on the destination file, and since the
> > NFSv4.2 protocol does not require you to perform any other operation in
> > order to persist data/metadata, I'm worried that we may be corrupting
> > the cloned file if the NFS server crashes at the wrong moment after the
> > client has been told the clone completed.
>
> That analysis seems correct.
>
> --D
>
> > Cheers
> >   Trond
> > --
> > Trond Myklebust
> > Linux NFS client maintainer, Hammerspace
> > trond.myklebust@hammerspace.com
> >
> >


--=20
Filipe David Manana,

=E2=80=9CWhether you think you can, or you think you can't =E2=80=94 you're=
 right.=E2=80=9D