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When a filesystem is exported to NFS clients, NFSv4 state (opens, locks, delegations, layouts) holds references that prevent the underlying filesystem from being unmounted. NFSD_CMD_UNLOCK_FILESYSTEM addresses this at superblock granularity, but administrators unexporting a single path on a shared filesystem (e.g., one of several exports on the same device) need finer control. Add NFSD_CMD_UNLOCK_EXPORT, which revokes NFSv4 state acquired through exports of a specific path. Matching is by path identity (dentry + vfsmount) via the sc_export field on each nfs4_stid, so multiple svc_export objects for the same path -- one per auth_domain -- are handled correctly without requiring the caller to name a specific client. The command takes a single "path" attribute. Userspace (exportfs -u) sends this after removing the last client for a given path, enabling the underlying filesystem to be unmounted. When multiple clients share an export path, individual unexports do not trigger state revocation; only the final one does. Reviewed-by: Jeff Layton <jlayton@kernel.org> Tested-by: Dai Ngo <dai.ngo@oracle.com> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>