diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 143da2e..d8148cc 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -50,11 +50,6 @@ enum {
 	NFSPROC4_CLNT_CB_SEQUENCE,
 };
 
-enum nfs_cb_opnum4 {
-	OP_CB_RECALL            = 4,
-	OP_CB_SEQUENCE          = 11,
-};
-
 #define NFS4_MAXTAGLEN		20
 
 #define NFS4_enc_cb_null_sz		0
@@ -80,30 +75,6 @@ enum nfs_cb_opnum4 {
 					op_dec_sz)
 
 /*
-* Generic encode routines from fs/nfs/nfs4xdr.c
-*/
-static inline __be32 *
-xdr_writemem(__be32 *p, const void *ptr, int nbytes)
-{
-	int tmp = XDR_QUADLEN(nbytes);
-	if (!tmp)
-		return p;
-	p[tmp-1] = 0;
-	memcpy(p, ptr, nbytes);
-	return p + tmp;
-}
-
-#define WRITE32(n)               *p++ = htonl(n)
-#define WRITEMEM(ptr,nbytes)     do {                           \
-	p = xdr_writemem(p, ptr, nbytes);                       \
-} while (0)
-#define RESERVE_SPACE(nbytes)   do {                            \
-	p = xdr_reserve_space(xdr, nbytes);                     \
-	if (!p) dprintk("NFSD: RESERVE_SPACE(%d) failed in function %s\n", (int) (nbytes), __func__); \
-	BUG_ON(!p);                                             \
-} while (0)
-
-/*
  * Generic decode routines from fs/nfs/nfs4xdr.c
  */
 #define DECODE_TAIL                             \
@@ -197,102 +168,232 @@ nfs_cb_stat_to_errno(int stat)
 	return stat;
 }
 
+static __be32 *xdr_encode_empty_array(__be32 *p)
+{
+	*p++ = xdr_zero;
+	return p;
+}
+
+/*
+ * Encode/decode NFSv4 CB basic data types
+ *
+ * Basic NFSv4 callback data types are defined in section 15 of RFC
+ * 3530: "Network File System (NFS) version 4 Protocol" and section
+ * 20 of RFC 5661: "Network File System (NFS) Version 4 Minor Version
+ * 1 Protocol"
+ */
+
+/*
+ *	nfs_cb_opnum4
+ *
+ *	enum nfs_cb_opnum4 {
+ *		OP_CB_GETATTR		= 3,
+ *		  ...
+ *	};
+ */
+enum nfs_cb_opnum4 {
+	OP_CB_GETATTR			= 3,
+	OP_CB_RECALL			= 4,
+	OP_CB_LAYOUTRECALL		= 5,
+	OP_CB_NOTIFY			= 6,
+	OP_CB_PUSH_DELEG		= 7,
+	OP_CB_RECALL_ANY		= 8,
+	OP_CB_RECALLABLE_OBJ_AVAIL	= 9,
+	OP_CB_RECALL_SLOT		= 10,
+	OP_CB_SEQUENCE			= 11,
+	OP_CB_WANTS_CANCELLED		= 12,
+	OP_CB_NOTIFY_LOCK		= 13,
+	OP_CB_NOTIFY_DEVICEID		= 14,
+	OP_CB_ILLEGAL			= 10044
+};
+
+static void encode_nfs_cb_opnum4(struct xdr_stream *xdr, enum nfs_cb_opnum4 op)
+{
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, 4);
+	*p = cpu_to_be32(op);
+}
+
+/*
+ * nfs_fh4
+ *
+ *	typedef opaque nfs_fh4<NFS4_FHSIZE>;
+ */
+static void encode_nfs_fh4(struct xdr_stream *xdr, const struct knfsd_fh *fh)
+{
+	u32 length = fh->fh_size;
+	__be32 *p;
+
+	BUG_ON(length > NFS4_FHSIZE);
+	p = xdr_reserve_space(xdr, 4 + length);
+	xdr_encode_opaque(p, &fh->fh_base, length);
+}
+
 /*
- * XDR encode
+ * stateid4
+ *
+ *	struct stateid4 {
+ *		uint32_t	seqid;
+ *		opaque		other[12];
+ *	};
  */
+static void encode_stateid4(struct xdr_stream *xdr, const stateid_t *sid)
+{
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, NFS4_STATEID_SIZE);
+	*p++ = cpu_to_be32(sid->si_generation);
+	xdr_encode_opaque_fixed(p, &sid->si_opaque, NFS4_STATEID_OTHER_SIZE);
+}
 
-static void
-encode_stateid(struct xdr_stream *xdr, stateid_t *sid)
+/*
+ * sessionid4
+ *
+ *	typedef opaque sessionid4[NFS4_SESSIONID_SIZE];
+ */
+static void encode_sessionid4(struct xdr_stream *xdr,
+			      const struct nfsd4_session *session)
 {
 	__be32 *p;
 
-	RESERVE_SPACE(sizeof(stateid_t));
-	WRITE32(sid->si_generation);
-	WRITEMEM(&sid->si_opaque, sizeof(stateid_opaque_t));
+	p = xdr_reserve_space(xdr, NFS4_MAX_SESSIONID_LEN);
+	xdr_encode_opaque_fixed(p, session->se_sessionid.data,
+					NFS4_MAX_SESSIONID_LEN);
 }
 
-static void
-encode_cb_compound_hdr(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr)
+/*
+ * CB_COMPOUND4args
+ *
+ *	struct CB_COMPOUND4args {
+ *		utf8str_cs	tag;
+ *		uint32_t	minorversion;
+ *		uint32_t	callback_ident;
+ *		nfs_cb_argop4	argarray<>;
+ *	};
+*/
+static void encode_cb_compound4args(struct xdr_stream *xdr,
+				    struct nfs4_cb_compound_hdr *hdr)
 {
 	__be32 * p;
 
-	RESERVE_SPACE(16);
-	WRITE32(0);            /* tag length is always 0 */
-	WRITE32(hdr->minorversion);
-	WRITE32(hdr->ident);
+	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4);
+	p = xdr_encode_empty_array(p);		/* empty tag */
+	*p++ = cpu_to_be32(hdr->minorversion);
+	*p++ = cpu_to_be32(hdr->ident);
+
 	hdr->nops_p = p;
-	WRITE32(hdr->nops);
+	*p = cpu_to_be32(hdr->nops);		/* argarray element count */
 }
 
+/*
+ * Update argarray element count
+ */
 static void encode_cb_nops(struct nfs4_cb_compound_hdr *hdr)
 {
-	*hdr->nops_p = htonl(hdr->nops);
+	BUG_ON(hdr->nops > NFS4_MAX_BACK_CHANNEL_OPS);
+	*hdr->nops_p = cpu_to_be32(hdr->nops);
 }
 
-static void
-encode_cb_recall(struct xdr_stream *xdr, struct nfs4_delegation *dp,
-		struct nfs4_cb_compound_hdr *hdr)
+/*
+ * CB_RECALL4args
+ *
+ *	struct CB_RECALL4args {
+ *		stateid4	stateid;
+ *		bool		truncate;
+ *		nfs_fh4		fh;
+ *	};
+ */
+static void encode_cb_recall4args(struct xdr_stream *xdr,
+				  const struct nfs4_delegation *dp,
+				  struct nfs4_cb_compound_hdr *hdr)
 {
 	__be32 *p;
-	int len = dp->dl_fh.fh_size;
-
-	RESERVE_SPACE(4);
-	WRITE32(OP_CB_RECALL);
-	encode_stateid(xdr, &dp->dl_stateid);
-	RESERVE_SPACE(8 + (XDR_QUADLEN(len) << 2));
-	WRITE32(0); /* truncate optimization not implemented */
-	WRITE32(len);
-	WRITEMEM(&dp->dl_fh.fh_base, len);
+
+	encode_nfs_cb_opnum4(xdr, OP_CB_RECALL);
+	encode_stateid4(xdr, &dp->dl_stateid);
+
+	p = xdr_reserve_space(xdr, 4);
+	*p++ = xdr_zero;			/* truncate */
+
+	encode_nfs_fh4(xdr, &dp->dl_fh);
+
 	hdr->nops++;
 }
 
-static void
-encode_cb_sequence(struct xdr_stream *xdr, struct nfsd4_callback *cb,
-		   struct nfs4_cb_compound_hdr *hdr)
+/*
+ * CB_SEQUENCE4args
+ *
+ *	struct CB_SEQUENCE4args {
+ *		sessionid4		csa_sessionid;
+ *		sequenceid4		csa_sequenceid;
+ *		slotid4			csa_slotid;
+ *		slotid4			csa_highest_slotid;
+ *		bool			csa_cachethis;
+ *		referring_call_list4	csa_referring_call_lists<>;
+ *	};
+ */
+static void encode_cb_sequence4args(struct xdr_stream *xdr,
+				    const struct nfsd4_callback *cb,
+				    struct nfs4_cb_compound_hdr *hdr)
 {
+	struct nfsd4_session *session = cb->cb_clp->cl_cb_session;
 	__be32 *p;
-	struct nfsd4_session *ses = cb->cb_clp->cl_cb_session;
 
 	if (hdr->minorversion == 0)
 		return;
 
-	RESERVE_SPACE(1 + NFS4_MAX_SESSIONID_LEN + 20);
+	encode_nfs_cb_opnum4(xdr, OP_CB_SEQUENCE);
+	encode_sessionid4(xdr, session);
+
+	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4 + 4);
+	*p++ = cpu_to_be32(session->se_cb_seq_nr);	/* csa_sequenceid */
+	*p++ = xdr_zero;			/* csa_slotid */
+	*p++ = xdr_zero;			/* csa_highest_slotid */
+	*p++ = xdr_zero;			/* csa_cachethis */
+	xdr_encode_empty_array(p);		/* csa_referring_call_lists */
 
-	WRITE32(OP_CB_SEQUENCE);
-	WRITEMEM(ses->se_sessionid.data, NFS4_MAX_SESSIONID_LEN);
-	WRITE32(ses->se_cb_seq_nr);
-	WRITE32(0);		/* slotid, always 0 */
-	WRITE32(0);		/* highest slotid always 0 */
-	WRITE32(0);		/* cachethis always 0 */
-	WRITE32(0); /* FIXME: support referring_call_lists */
 	hdr->nops++;
 }
 
-static int
-nfs4_xdr_enc_cb_null(struct rpc_rqst *req, __be32 *p)
+/*
+ * NFSv4.0 and NFSv4.1 XDR encode functions
+ *
+ * NFSv4.0 callback argument types are defined in section 15 of RFC
+ * 3530: "Network File System (NFS) version 4 Protocol" and section 20
+ * of RFC 5661:  "Network File System (NFS) Version 4 Minor Version 1
+ * Protocol".
+ */
+
+/*
+ * NB: Without this zero space reservation, callbacks over krb5p fail
+ */
+static int nfs4_xdr_enc_cb_null(struct rpc_rqst *req, __be32 *p, void *__unused)
 {
 	struct xdr_stream xdrs, *xdr = &xdrs;
 
 	xdr_init_encode(&xdrs, &req->rq_snd_buf, p);
-        RESERVE_SPACE(0);
+	xdr_reserve_space(xdr, 0);
 	return 0;
 }
 
-static int
-nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, __be32 *p,
-		struct nfsd4_callback *cb)
+/*
+ * 20.2. Operation 4: CB_RECALL - Recall a Delegation
+ */
+static int nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, __be32 *p,
+				  const struct nfsd4_callback *cb)
 {
 	struct xdr_stream xdr;
-	struct nfs4_delegation *args = cb->cb_op;
+	const struct nfs4_delegation *args = cb->cb_op;
 	struct nfs4_cb_compound_hdr hdr = {
 		.ident = cb->cb_clp->cl_cb_ident,
 		.minorversion = cb->cb_minorversion,
 	};
 
 	xdr_init_encode(&xdr, &req->rq_snd_buf, p);
-	encode_cb_compound_hdr(&xdr, &hdr);
-	encode_cb_sequence(&xdr, cb, &hdr);
-	encode_cb_recall(&xdr, args, &hdr);
+	encode_cb_compound4args(&xdr, &hdr);
+	encode_cb_sequence4args(&xdr, cb, &hdr);
+	encode_cb_recall4args(&xdr, args, &hdr);
 	encode_cb_nops(&hdr);
 	return 0;
 }
