NFSD: Replace READ* macros in nfsd4_decode_bind_conn_to_session()

A dedicated sessionid4 decoder is introduced that will be used by
other operation decoders in subsequent patches.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -664,6 +664,19 @@ nfsd4_decode_state_owner4(struct nfsd4_compoundargs *argp,
 	return nfsd4_decode_opaque(argp, owner);
 }
 
+static __be32
+nfsd4_decode_sessionid4(struct nfsd4_compoundargs *argp,
+			struct nfs4_sessionid *sessionid)
+{
+	__be32 *p;
+
+	p = xdr_inline_decode(argp->xdr, NFS4_MAX_SESSIONID_LEN);
+	if (!p)
+		return nfserr_bad_xdr;
+	memcpy(sessionid->data, p, sizeof(sessionid->data));
+	return nfs_ok;
+}
+
 /* Defined in Appendix A of RFC 5531 */
 static __be32
 nfsd4_decode_authsys_parms(struct nfsd4_compoundargs *argp,
@@ -788,18 +801,6 @@ nfsd4_decode_access(struct nfsd4_compoundargs *argp,
 	return nfs_ok;
 }
 
-static __be32 nfsd4_decode_bind_conn_to_session(struct nfsd4_compoundargs *argp, struct nfsd4_bind_conn_to_session *bcts)
-{
-	DECODE_HEAD;
-
-	READ_BUF(NFS4_MAX_SESSIONID_LEN + 8);
-	COPYMEM(bcts->sessionid.data, NFS4_MAX_SESSIONID_LEN);
-	bcts->dir = be32_to_cpup(p++);
-	/* XXX: skipping ctsa_use_conn_in_rdma_mode.  Perhaps Tom Tucker
-	 * could help us figure out we should be using it. */
-	DECODE_TAIL;
-}
-
 static __be32
 nfsd4_decode_close(struct nfsd4_compoundargs *argp, struct nfsd4_close *close)
 {
@@ -1479,6 +1480,22 @@ static __be32 nfsd4_decode_backchannel_ctl(struct nfsd4_compoundargs *argp, stru
 	return nfsd4_decode_cb_sec(argp, &bc->bc_cb_sec);
 }
 
+static __be32 nfsd4_decode_bind_conn_to_session(struct nfsd4_compoundargs *argp, struct nfsd4_bind_conn_to_session *bcts)
+{
+	u32 use_conn_in_rdma_mode;
+	__be32 status;
+
+	status = nfsd4_decode_sessionid4(argp, &bcts->sessionid);
+	if (status)
+		return status;
+	if (xdr_stream_decode_u32(argp->xdr, &bcts->dir) < 0)
+		return nfserr_bad_xdr;
+	if (xdr_stream_decode_u32(argp->xdr, &use_conn_in_rdma_mode) < 0)
+		return nfserr_bad_xdr;
+
+	return nfs_ok;
+}
+
 static __be32
 nfsd4_decode_exchange_id(struct nfsd4_compoundargs *argp,
 			 struct nfsd4_exchange_id *exid)