NFSD: Add a helper to decode state_protect4_a

Refactor for clarity.

Also, remove a stale comment. Commit ed941643 ("nfsd: implement
machine credential support for some operations") added support for
SP4_MACH_CRED, so state_protect_a is no longer completely ignored.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -3066,7 +3066,7 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 
 	rpc_ntop(sa, addr_str, sizeof(addr_str));
 	dprintk("%s rqstp=%p exid=%p clname.len=%u clname.data=%p "
-		"ip_addr=%s flags %x, spa_how %d\n",
+		"ip_addr=%s flags %x, spa_how %u\n",
 		__func__, rqstp, exid, exid->clname.len, exid->clname.data,
 		addr_str, exid->flags, exid->spa_how);
 

fs/nfsd/nfs4xdr.c

@@ -1531,25 +1531,13 @@ nfsd4_decode_ssv_sp_parms(struct nfsd4_compoundargs *argp,
 }
 
 static __be32
-nfsd4_decode_exchange_id(struct nfsd4_compoundargs *argp,
+nfsd4_decode_state_protect4_a(struct nfsd4_compoundargs *argp,
 			      struct nfsd4_exchange_id *exid)
 {
-	DECODE_HEAD;
-	int dummy;
-
-	READ_BUF(NFS4_VERIFIER_SIZE);
-	COPYMEM(exid->verifier.data, NFS4_VERIFIER_SIZE);
+	__be32 status;
 
-	status = nfsd4_decode_opaque(argp, &exid->clname);
-	if (status)
+	if (xdr_stream_decode_u32(argp->xdr, &exid->spa_how) < 0)
 		return nfserr_bad_xdr;
-
-	READ_BUF(4);
-	exid->flags = be32_to_cpup(p++);
-
-	/* Ignore state_protect4_a */
-	READ_BUF(4);
-	exid->spa_how = be32_to_cpup(p++);
 	switch (exid->spa_how) {
 	case SP4_NONE:
 		break;
@@ -1564,9 +1552,31 @@ nfsd4_decode_exchange_id(struct nfsd4_compoundargs *argp,
 			return status;
 		break;
 	default:
-		goto xdr_error;
+		return nfserr_bad_xdr;
 	}
 
+	return nfs_ok;
+}
+
+static __be32
+nfsd4_decode_exchange_id(struct nfsd4_compoundargs *argp,
+			 struct nfsd4_exchange_id *exid)
+{
+	DECODE_HEAD;
+	int dummy;
+
+	status = nfsd4_decode_verifier4(argp, &exid->verifier);
+	if (status)
+		return status;
+	status = nfsd4_decode_opaque(argp, &exid->clname);
+	if (status)
+		return status;
+	if (xdr_stream_decode_u32(argp->xdr, &exid->flags) < 0)
+		return nfserr_bad_xdr;
+	status = nfsd4_decode_state_protect4_a(argp, exid);
+	if (status)
+		return status;
+
 	READ_BUF(4);    /* nfs_impl_id4 array length */
 	dummy = be32_to_cpup(p++);
 

fs/nfsd/xdr4.h

@@ -433,7 +433,7 @@ struct nfsd4_exchange_id {
 	u32		flags;
 	clientid_t	clientid;
 	u32		seqid;
-	int		spa_how;
+	u32		spa_how;
 	u32             spo_must_enforce[3];
 	u32             spo_must_allow[3];
 	struct xdr_netobj nii_domain;