mds/Server: fix LOOKUPSNAP

The current LOOKUPSNAP code path was dereferencing mdr->dn[0] and getting
SEGV.  Instead, set the do_lookup arg to false for getattr so that we do
not try to dereference this; for snaps it will always be NULL as we are
constructing a fake namespace for the .snap directory.  (This happens in
the path_traverse, the result of which is to set snapid--without any real
dentry).

With this fix, snaptest-0.sh passes.

Signed-off-by: Sage Weil <[email protected]>
Reviewed-by: Greg Farnum <[email protected]>

src/mds/Server.cc

@@ -1167,10 +1167,11 @@ void Server::dispatch_client_request(MDRequest *mdr)
 
     // inodes ops.
   case CEPH_MDS_OP_LOOKUP:
-  case CEPH_MDS_OP_LOOKUPSNAP:
     handle_client_getattr(mdr, true);
     break;
 
+  case CEPH_MDS_OP_LOOKUPSNAP:
+    // lookupsnap does not reference a CDentry; treat it as a getattr
   case CEPH_MDS_OP_GETATTR:
     handle_client_getattr(mdr, false);
     break;