On Wed, Nov 27, 2019 at 12:21:36PM -0800, Darrick J. Wong 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. So we need to call xfs_fs_nfs_commit_metadata() to get that done post vfs_clone_file_range() completion on the server side, yes? > > (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. Yup, that's exactly what server side calls to commit_metadata() are supposed to address. I suspect to be correct, this might require commit_metadata() to be called on both the source and destination inodes, as both of them may have modified metadata as a result of the clone operation. For XFS one of them will be a no-op, but for other filesystems that don't implement ->commit_metadata, we'll need to call sync_inode_metadata() on both inodes... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
