nfsd4: introduce nfs4_client.cl_refcount

Currently just initialize the cl_refcount to 1
and decrement in expire_client(), conditionally freeing the
client when the refcount reaches 0.

To be used later by nfsv4.1 compounds to keep the client from
timing out while in use.
Signed-off-by: NBenny Halevy <bhalevy@panasas.com>
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4state.c

@@ -740,8 +740,9 @@ expire_client(struct nfs4_client *clp)
 	list_del(&clp->cl_strhash);
 	spin_lock(&client_lock);
 	unhash_client_locked(clp);
-	spin_unlock(&client_lock);
+	if (atomic_read(&clp->cl_refcount) == 0)
 		free_client(clp);
+	spin_unlock(&client_lock);
 }
 
 static void copy_verf(struct nfs4_client *target, nfs4_verifier *source)
@@ -827,6 +828,7 @@ static struct nfs4_client *create_client(struct xdr_netobj name, char *recdir,
 	}
 
 	memcpy(clp->cl_recdir, recdir, HEXDIR_LEN);
+	atomic_set(&clp->cl_refcount, 0);
 	atomic_set(&clp->cl_cb_set, 0);
 	INIT_LIST_HEAD(&clp->cl_idhash);
 	INIT_LIST_HEAD(&clp->cl_strhash);

fs/nfsd/state.h

@@ -233,6 +233,8 @@ struct nfs4_client {
 	struct nfsd4_clid_slot	cl_cs_slot;	/* create_session slot */
 	u32			cl_exchange_flags;
 	struct nfs4_sessionid	cl_sessionid;
+	/* number of rpc's in progress over an associated session: */
+	atomic_t		cl_refcount;
 
 	/* for nfs41 callbacks */
 	/* We currently support a single back channel with a single slot */