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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Trond Myklebust <trondmy@hammerspace.com>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: Question about clone_range() metadata stability
Date: Wed, 27 Nov 2019 12:21:36 -0800
Message-ID: <20191127202136.GV6211@magnolia> (raw)
In-Reply-To: <f063089fb62c219ea6453c7b9b0aaafd50946dae.camel@hammerspace.com>

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.)

> 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
> 
> 

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27 18:38 Trond Myklebust
2019-11-27 20:21 ` Darrick J. Wong [this message]
2019-11-29 12:43   ` Filipe Manana
2019-12-01 21:05   ` Dave Chinner
2019-12-02 17:09     ` Darrick J. Wong
2019-12-03  7:36     ` Trond Myklebust
2019-12-03 16:35       ` Darrick J. Wong
2019-12-03 23:00         ` Trond Myklebust
2019-12-06  1:31       ` Dave Chinner

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