nfsd: stop pretending that we cache the SEQUENCE reply.

nfsd does not cache the reply to a SEQUENCE.  As the comment above
nfsd4_replay_cache_entry() says:

 * The sequence operation is not cached because we can use the slot and
 * session values.

The comment above nfsd4_cache_this() suggests otherwise.

 * The session reply cache only needs to cache replies that the client
 * actually asked us to.  But it's almost free for us to cache compounds
 * consisting of only a SEQUENCE op, so we may as well cache those too.
 * Also, the protocol doesn't give us a convenient response in the case
 * of a replay of a solo SEQUENCE op that wasn't cached

The code in nfsd4_store_cache_entry() makes it clear that only responses
beyond 'cstate.data_offset' are actually cached, and data_offset is set
at the end of nfsd4_encode_sequence() *after* the sequence response has
been encoded.

This patch simplifies code and removes the confusing comments.

- nfsd4_is_solo_sequence() is discarded as not-useful.
- nfsd4_cache_this() is now trivial so it too is discarded with the
  code placed in-line at the one call-site in nfsd4_store_cache_entry().
- nfsd4_enc_sequence_replay() is open-coded in to
  nfsd4_replay_cache_entry(), and then simplified to (hopefully) make
  the process of replaying a reply clearer.

Signed-off-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: neilbrown

fs/nfsd/nfs4state.c

@@ -3508,7 +3508,7 @@ nfsd4_store_cache_entry(struct nfsd4_compoundres *resp)
 	free_svc_cred(&slot->sl_cred);
 	copy_cred(&slot->sl_cred, &resp->rqstp->rq_cred);
 
-	if (!nfsd4_cache_this(resp)) {
+	if (!(resp->cstate.slot->sl_flags & NFSD4_SLOT_CACHETHIS)) {
 		slot->sl_flags &= ~NFSD4_SLOT_CACHED;
 		return;
 	}
@@ -3522,41 +3522,6 @@ nfsd4_store_cache_entry(struct nfsd4_compoundres *resp)
 	return;
 }
 
-/*
- * Encode the replay sequence operation from the slot values.
- * If cachethis is FALSE encode the uncached rep error on the next
- * operation which sets resp->p and increments resp->opcnt for
- * nfs4svc_encode_compoundres.
- *
- */
-static __be32
-nfsd4_enc_sequence_replay(struct nfsd4_compoundargs *args,
-			  struct nfsd4_compoundres *resp)
-{
-	struct nfsd4_op *op;
-	struct nfsd4_slot *slot = resp->cstate.slot;
-
-	/* Encode the replayed sequence operation */
-	op = &args->ops[resp->opcnt - 1];
-	nfsd4_encode_operation(resp, op);
-
-	if (slot->sl_flags & NFSD4_SLOT_CACHED)
-		return op->status;
-	if (args->opcnt == 1) {
-		/*
-		 * The original operation wasn't a solo sequence--we
-		 * always cache those--so this retry must not match the
-		 * original:
-		 */
-		op->status = nfserr_seq_false_retry;
-	} else {
-		op = &args->ops[resp->opcnt++];
-		op->status = nfserr_retry_uncached_rep;
-		nfsd4_encode_operation(resp, op);
-	}
-	return op->status;
-}
-
 /*
  * The sequence operation is not cached because we can use the slot and
  * session values.
@@ -3565,17 +3530,30 @@ static __be32
 nfsd4_replay_cache_entry(struct nfsd4_compoundres *resp,
 			 struct nfsd4_sequence *seq)
 {
+	struct nfsd4_compoundargs *args = resp->rqstp->rq_argp;
 	struct nfsd4_slot *slot = resp->cstate.slot;
 	struct xdr_stream *xdr = resp->xdr;
 	__be32 *p;
-	__be32 status;
 
 	dprintk("--> %s slot %p\n", __func__, slot);
 
-	status = nfsd4_enc_sequence_replay(resp->rqstp->rq_argp, resp);
-	if (status)
-		return status;
+	/* Always encode the SEQUENCE response. */
+	nfsd4_encode_operation(resp, &args->ops[0]);
+	if (args->opcnt == 1)
+		/* A solo SEQUENCE - nothing was cached */
+		return args->ops[0].status;
+
+	if (!(slot->sl_flags & NFSD4_SLOT_CACHED)) {
+		/* We weren't asked to cache this. */
+		struct nfsd4_op *op;
+
+		op = &args->ops[resp->opcnt++];
+		op->status = nfserr_retry_uncached_rep;
+		nfsd4_encode_operation(resp, op);
+		return op->status;
+	}
 
+	/* return reply from cache */
 	p = xdr_reserve_space(xdr, slot->sl_datalen);
 	if (!p) {
 		WARN_ON_ONCE(1);

fs/nfsd/xdr4.h

@@ -924,27 +924,6 @@ struct nfsd4_compoundres {
 	struct nfsd4_compound_state	cstate;
 };
 
-static inline bool nfsd4_is_solo_sequence(struct nfsd4_compoundres *resp)
-{
-	struct nfsd4_compoundargs *args = resp->rqstp->rq_argp;
-	return resp->opcnt == 1 && args->ops[0].opnum == OP_SEQUENCE;
-}
-
-/*
- * The session reply cache only needs to cache replies that the client
- * actually asked us to.  But it's almost free for us to cache compounds
- * consisting of only a SEQUENCE op, so we may as well cache those too.
- * Also, the protocol doesn't give us a convenient response in the case
- * of a replay of a solo SEQUENCE op that wasn't cached
- * (RETRY_UNCACHED_REP can only be returned in the second op of a
- * compound).
- */
-static inline bool nfsd4_cache_this(struct nfsd4_compoundres *resp)
-{
-	return (resp->cstate.slot->sl_flags & NFSD4_SLOT_CACHETHIS)
-		|| nfsd4_is_solo_sequence(resp);
-}
-
 static inline bool nfsd4_last_compound_op(struct svc_rqst *rqstp)
 {
 	struct nfsd4_compoundres *resp = rqstp->rq_resp;