mds: store layout on header object

This is surprisingly simple because we were already redundantly
calling store_backtrace whenever the layout changed!  That was
a side effect of the way add_old_pool is handled, the backtrace
version is bumped to latest even if the "old" pool is the
current one.

The upshot is that if we accept the existing behaviour of
also unnecessarily updating the 'parent' xattr, keeping
the new 'layout' xattr update requires no new dirty flags.  This
is a twitchy enough behaviour that new tests are needed to guard
against regressions though.

Fixes: #4161
Signed-off-by: John Spray <john.spray@redhat.com>

diff --git a/src/mds/CInode.cc b/src/mds/CInode.cc
index a9366265e76306afd4aed1aafe1ad3bec57d3ccb..d798448e6b7c51b7be1cc6e0cf7a967b0d54d24d 100644 (file)
--- a/src/mds/CInode.cc
+++ b/src/mds/CInode.cc
@@ -1124,20 +1124,25 @@ void CInode::store_backtrace(MDSInternalContextBase *fin, int op_prio)
   auth_pin(this);
 
   int64_t pool;
-  if (is_dir())
+  if (is_dir()) {
     pool = mdcache->mds->mdsmap->get_metadata_pool();
-  else
+  } else {
     pool = inode.layout.fl_pg_pool;
+  }
 
   inode_backtrace_t bt;
   build_backtrace(pool, bt);
-  bufferlist bl;
-  ::encode(bt, bl);
+  bufferlist parent_bl;
+  ::encode(bt, parent_bl);
 
   ObjectOperation op;
   op.priority = op_prio;
   op.create(false);
-  op.setxattr("parent", bl);
+  op.setxattr("parent", parent_bl);
+
+  bufferlist layout_bl;
+  ::encode(inode.layout, layout_bl);
+  op.setxattr("layout", layout_bl);
 
   SnapContext snapc;
   object_t oid = get_object_name(ino(), frag_t(), "");
@@ -1147,6 +1152,7 @@ void CInode::store_backtrace(MDSInternalContextBase *fin, int op_prio)
     &mdcache->mds->finisher);
 
   if (!state_test(STATE_DIRTYPOOL) || inode.old_pools.empty()) {
+    dout(20) << __func__ << ": no dirtypool or no old pools" << dendl;
     mdcache->mds->objecter->mutate(oid, oloc, op, snapc, ceph_clock_now(g_ceph_context),
                                   0, NULL, fin2);
     return;
@@ -1156,16 +1162,21 @@ void CInode::store_backtrace(MDSInternalContextBase *fin, int op_prio)
   mdcache->mds->objecter->mutate(oid, oloc, op, snapc, ceph_clock_now(g_ceph_context),
                                 0, NULL, gather.new_sub());
 
+  // In the case where DIRTYPOOL is set, we update all old pools backtraces
+  // such that anyone reading them will see the new pool ID in
+  // inode_backtrace_t::pool and go read everything else from there.
   for (compact_set<int64_t>::iterator p = inode.old_pools.begin();
        p != inode.old_pools.end();
        ++p) {
     if (*p == pool)
       continue;
 
+    dout(20) << __func__ << ": updating old pool " << *p << dendl;
+
     ObjectOperation op;
     op.priority = op_prio;
     op.create(false);
-    op.setxattr("parent", bl);
+    op.setxattr("parent", parent_bl);
 
     object_locator_t oloc(*p);
     mdcache->mds->objecter->mutate(oid, oloc, op, snapc, ceph_clock_now(g_ceph_context),