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: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 98836fd..ee42a0b 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -233,6 +233,8 @@
 	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 */