pNFS/flexfiles: Only send layoutstats updates for mirrors that were updated

If there have been no reads or writes to a given mirror since the last
layoutstats update, then don't resend the same data.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index 3ee0c9f..09f292e 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -81,12 +81,15 @@ struct nfs4_ff_layout_mirror {
 	struct rpc_cred	__rcu		*rw_cred;
 	atomic_t			ref;
 	spinlock_t			lock;
+	unsigned long			flags;
 	struct nfs4_ff_layoutstat	read_stat;
 	struct nfs4_ff_layoutstat	write_stat;
 	ktime_t				start_time;
 	u32				report_interval;
 };
 
+#define NFS4_FF_MIRROR_STAT_AVAIL	(0)
+
 struct nfs4_ff_layout_segment {
 	struct pnfs_layout_segment	generic_hdr;
 	u64				stripe_unit;