nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED

A 4.1 server must notify a client that has had any state revoked using
the SEQ4_STATUS_RECALLABLE_STATE_REVOKED flag.  The client can figure
out exactly which state is the problem using CHECK_STATEID and then free
it using FREE_STATEID.  The status flag will be unset once all such
revoked stateids are freed.

Our server's only recallable state is delegations.  So we keep with each
4.1 client a list of delegations that have timed out and been recalled,
but haven't yet been freed by FREE_STATEID.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 13ec485..274e2a1 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -79,6 +79,8 @@
 #define NFS4_DELEG_STID 4
 /* For an open stateid kept around *only* to process close replays: */
 #define NFS4_CLOSED_STID 8
+/* For a deleg stateid kept around only to process free_stateid's: */
+#define NFS4_REVOKED_DELEG_STID 16
 	unsigned char sc_type;
 	stateid_t sc_stateid;
 	struct nfs4_client *sc_client;
@@ -238,6 +240,7 @@
 	struct list_head	cl_openowners;
 	struct idr		cl_stateids;	/* stateid lookup */
 	struct list_head	cl_delegations;
+	struct list_head	cl_revoked;	/* unacknowledged, revoked 4.1 state */
 	struct list_head        cl_lru;         /* tail queue */
 	struct xdr_netobj	cl_name; 	/* id generated by client */
 	nfs4_verifier		cl_verifier; 	/* generated by client */