From f4d9916826687778a4f68386a771171e5b0b0916 Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@newdream.net>
Date: Thu, 4 Mar 2010 13:34:54 -0800
Subject: [PATCH] mds: return lease on null dentries (ENOENT lookups)

This provides the client with a lease on a dentry's nonexistence,
allowing it to avoid repetitive ENOENT lookups.
---
 src/mds/MDCache.cc | 12 ++++++++++++
 src/mds/Server.cc  |  6 +++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/mds/MDCache.cc b/src/mds/MDCache.cc
index 6571dbdf37e4d..8d19040327258 100644
--- a/src/mds/MDCache.cc
+++ b/src/mds/MDCache.cc
@@ -5925,6 +5925,18 @@ int MDCache::path_traverse(MDRequest *mdr, Message *req,     // who
       // dentry is mine.
       if (curdir->is_complete()) {
         // file not found
+	if (pdnvec) {
+	  // instantiate a null dn
+	  if (dn) {
+	    dout(20) << " had null " << *dn << dendl;
+	    assert(dnl->is_null());
+	  } else {
+	    // create a null dentry
+	    dn = curdir->add_null_dentry(path[depth]);
+	    dout(20) << " added null " << *dn << dendl;
+	  }
+	  pdnvec->push_back(dn);
+	}
         return -ENOENT;
       } else {
 	// directory isn't complete; reload
diff --git a/src/mds/Server.cc b/src/mds/Server.cc
index 2ad5841e175e0..2baa795a3c417 100644
--- a/src/mds/Server.cc
+++ b/src/mds/Server.cc
@@ -1694,7 +1694,11 @@ CInode* Server::rdlock_path_pin_ref(MDRequest *mdr, int n,
   int r = mdcache->path_traverse(mdr, 0, refpath, &mdr->dn[n], &mdr->in[n], MDS_TRAVERSE_FORWARD);
   if (r > 0) return false; // delayed
   if (r < 0) {  // error
-    reply_request(mdr, r);
+    if (r == -ENOENT && n == 0) {
+      reply_request(mdr, r, NULL, mdr->dn[n][mdr->dn[n].size()-1]);
+    } else {
+      reply_request(mdr, r);
+    }
     return 0;
   }
   CInode *ref = mdr->in[n];
-- 
2.39.5