nfsd: add trace events

For now just a few simple events to trace the layout stateid lifetime, but
these already were enough to find several bugs in the Linux client layout
stateid handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index fa14359..d30bea8d 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -44,6 +44,7 @@
 #include "netns.h"
 #include "acl.h"
 #include "pnfs.h"
+#include "trace.h"
 
 #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 #include <linux/security.h>
@@ -1298,8 +1299,10 @@
 
 	nfserr = nfsd4_preprocess_layout_stateid(rqstp, cstate, &lgp->lg_sid,
 						true, lgp->lg_layout_type, &ls);
-	if (nfserr)
+	if (nfserr) {
+		trace_layout_get_lookup_fail(&lgp->lg_sid);
 		goto out;
+	}
 
 	nfserr = nfserr_recallconflict;
 	if (atomic_read(&ls->ls_stid.sc_file->fi_lo_recalls))
@@ -1359,6 +1362,7 @@
 						false, lcp->lc_layout_type,
 						&ls);
 	if (nfserr) {
+		trace_layout_commit_lookup_fail(&lcp->lc_sid);
 		/* fixup error code as per RFC5661 */
 		if (nfserr == nfserr_bad_stateid)
 			nfserr = nfserr_badlayout;