On Wed, Nov 27, 2019 at 8:24 PM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > 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@xxxxxxxxxxxxxxx > > > > -- Filipe David Manana, “Whether you think you can, or you think you can't — you're right.”
