crimson/osd: put snapmapper's key-value pairs into dedicated objs

Otherwise, PG::read_log_and_missing() will meet those key-values and
won't know what to do with them. This is modeling what the classic
osd is doing

Signed-off-by: Xuehan Xu <xuxuehan@qianxin.com>

src/crimson/osd/pg.cc

@@ -135,7 +135,7 @@ PG::PG(
     osdriver(
       &shard_services.get_store(),
       coll_ref,
-      pgid.make_pgmeta_oid()),
+      make_snapmapper_oid()),
     snap_mapper(
       this->shard_services.get_cct(),
       &osdriver,
@@ -596,7 +596,7 @@ void PG::schedule_renew_lease(epoch_t last_peering_reset, ceph::timespan delay)
 }
 
 
-void PG::init(
+seastar::future<> PG::init(
   int role,
   const vector<int>& newup, int new_up_primary,
   const vector<int>& newacting, int new_acting_primary,
@@ -607,6 +607,16 @@ void PG::init(
   peering_state.init(
     role, newup, new_up_primary, newacting,
     new_acting_primary, history, pi, t);
+  assert(coll_ref);
+  return shard_services.get_store().exists(
+    get_collection_ref(), make_snapmapper_oid()
+  ).safe_then([&t, this](bool existed) {
+      if (!existed) {
+        t.touch(coll_ref->get_cid(), make_snapmapper_oid());
+      }
+    },
+    ::crimson::ct_error::assert_all{"unexpected eio"}
+  );
 }
 
 seastar::future<> PG::read_state(crimson::os::FuturizedStore::Shard* store)

src/crimson/osd/pg.h

@@ -471,7 +471,7 @@ class PG : public boost::intrusive_ref_counter<
   }
 
   /// initialize created PG
-  void init(
+  seastar::future<> init(
     int role,
     const std::vector<int>& up,
     int up_primary,
@@ -646,6 +646,16 @@ class PG : public boost::intrusive_ref_counter<
   OSDriver osdriver;
   SnapMapper snap_mapper;
 
+  ghobject_t make_snapmapper_oid() {
+    return ghobject_t(hobject_t(
+      sobject_t(
+       object_t("snapmapper"),
+       0),
+      std::string(),
+      pgid.ps(),
+      pgid.pool(),
+      std::string()));
+  }
 public:
   // PeeringListener
   void publish_stats_to_osd() final;

src/crimson/osd/shard_services.cc

@@ -669,30 +669,31 @@ seastar::future<Ref<PG>> ShardServices::handle_pg_create_info(
 	    pg_shard_t(local_state.whoami, info->pgid.shard),
 	    acting);
 
-	  PeeringCtx rctx;
+	  std::unique_ptr<PeeringCtx> rctx = std::make_unique<PeeringCtx>();
 	  create_pg_collection(
-	    rctx.transaction,
+	    rctx->transaction,
 	    info->pgid,
 	    info->pgid.get_split_bits(pp->get_pg_num()));
 	  init_pg_ondisk(
-	    rctx.transaction,
+	    rctx->transaction,
 	    info->pgid,
 	    pp);
 
-	  pg->init(
+	  return pg->init(
 	    role,
 	    up,
 	    up_primary,
 	    acting,
 	    acting_primary,
 	    info->history,
 	    info->past_intervals,
-	    rctx.transaction);
-
-	  return start_operation<PGAdvanceMap>(
-	    pg, *this, get_map()->get_epoch(), std::move(rctx), true
-	  ).second.then([pg=pg] {
-	    return seastar::make_ready_future<Ref<PG>>(pg);
+	    rctx->transaction
+	  ).then([this, pg=pg, rctx=std::move(rctx)] {
+	    return start_operation<PGAdvanceMap>(
+	      pg, *this, get_map()->get_epoch(), std::move(*rctx), true
+	    ).second.then([pg=pg] {
+	      return seastar::make_ready_future<Ref<PG>>(pg);
+	    });
 	  });
 	});
     });