[PATCH] knfsd: idempotent replay cache for OPEN state

This implements the idempotent replay cache need for NFSv4 OPEN state.
each state owner (open owner or lock owner) is required to store the
last sequence number mutating operation, and retransmit it when replayed
sequence number is presented for the operation.

I've implemented the cache as a static buffer of size 112 bytes
(NFSD4_REPLAY_ISIZE) which is large enough to hold the OPEN, the largest
of the sequence mutation operations.  This implements the cache for
OPEN, OPEN_CONFIRM, OPEN_DOWNGRADE, and CLOSE.  LOCK and UNLOCK will be
added when byte-range locking is done (soon!).

2 files changed, 24 insertions, 0 deletions

diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
index 66422a1c8277..b4d10b7dcc16 100644
--- a/include/linux/nfsd/state.h
+++ b/include/linux/nfsd/state.h
@@ -95,6 +95,27 @@ update_stateid(stateid_t *stateid)
 	stateid->si_generation++;
 }
 
+/* A reasonable value for REPLAY_ISIZE was estimated as follows:  
+ * The OPEN response, typically the largest, requires 
+ *   4(status) + 8(stateid) + 20(changeinfo) + 4(rflags) +  8(verifier) + 
+ *   4(deleg. type) + 8(deleg. stateid) + 4(deleg. recall flag) + 
+ *   20(deleg. space limit) + ~32(deleg. ace) = 112 bytes 
+ */
+
+#define NFSD4_REPLAY_ISIZE       112 
+
+/*
+ * Replay buffer, where the result of the last seqid-mutating operation 
+ * is cached. 
+ */
+struct nfs4_replay {
+	u32			rp_status;
+	unsigned int		rp_buflen;
+	char			*rp_buf;
+	unsigned		intrp_allocated;
+	char			rp_ibuf[NFSD4_REPLAY_ISIZE];
+};
+
 /*
 * nfs4_stateowner can either be an open_owner, or (eventually) a lock_owner
 *
@@ -111,6 +132,7 @@ struct nfs4_stateowner {
 	u32                     so_seqid;    
 	struct xdr_netobj       so_owner;     /* open owner name */
 	int                     so_confirmed; /* successful OPEN_CONFIRM? */
+	struct nfs4_replay	so_replay;
 };
 
 /*
diff --git a/include/linux/nfsd/xdr4.h b/include/linux/nfsd/xdr4.h
index 54c3049f6068..254d5d2c5647 100644
--- a/include/linux/nfsd/xdr4.h
+++ b/include/linux/nfsd/xdr4.h
@@ -284,6 +284,7 @@ struct nfsd4_op {
 		struct nfsd4_verify		verify;
 		struct nfsd4_write		write;
 	} u;
+	struct nfs4_replay *			replay;
 };
 
 struct nfsd4_compoundargs {
@@ -339,6 +340,7 @@ int nfs4svc_decode_compoundargs(struct svc_rqst *, u32 *,
 int nfs4svc_encode_compoundres(struct svc_rqst *, u32 *, 
 		struct nfsd4_compoundres *);
 void nfsd4_encode_operation(struct nfsd4_compoundres *, struct nfsd4_op *);
+void nfsd4_encode_replay(struct nfsd4_compoundres *resp, struct nfsd4_op *op);
 int nfsd4_encode_fattr(struct svc_fh *fhp, struct svc_export *exp,
 		       struct dentry *dentry, u32 *buffer, int *countp, 
 		       u32 *bmval);