osd: add OSD_BITWISE_HOBJ_SORT feature

We will sort [g]hobject_t's bitwise (instead of nibblewise) if all
OSDs who have participated in peering support the feature.

Note that this means a latecomer PG who does a notify may not have
the feature while the acting set operates with the new sort order.
We will need to be careful about last_backfill in this case.. that patch
it coming.

Signed-off-by: Sage Weil <sage@redhat.com>

src/include/ceph_features.h

@@ -64,6 +64,7 @@
 // duplicated since it was introduced at the same time as MIN_SIZE_RECOVERY
 #define CEPH_FEATURE_OSD_PROXY_FEATURES (1ULL<<49)  /* overlap w/ above */
 #define CEPH_FEATURE_MON_METADATA (1ULL<<50)
+#define CEPH_FEATURE_OSD_BITWISE_HOBJ_SORT (1ULL<<51) /* can sort objs bitwise */
 
 #define CEPH_FEATURE_RESERVED2 (1ULL<<61)  /* slow down, we are almost out... */
 #define CEPH_FEATURE_RESERVED  (1ULL<<62)  /* DO NOT USE THIS ... last bit! */
@@ -150,6 +151,7 @@ static inline unsigned long long ceph_sanitize_features(unsigned long long f) {
          CEPH_FEATURE_CRUSH_V4 |	     \
          CEPH_FEATURE_OSD_MIN_SIZE_RECOVERY |		 \
 	 CEPH_FEATURE_MON_METADATA |			 \
+	 CEPH_FEATURE_OSD_BITWISE_HOBJ_SORT |		 \
 	 0ULL)
 
 #define CEPH_FEATURES_SUPPORTED_DEFAULT  CEPH_FEATURES_ALL

src/osd/PG.h

@@ -2031,6 +2031,11 @@ class PG {
   void apply_acting_features(uint64_t f) { acting_features &= f; }
   void apply_upacting_features(uint64_t f) { upacting_features &= f; }
 
+  /// true if we will sort hobjects bitwise for this pg interval
+  bool get_sort_bitwise() const {
+    return get_min_upacting_features() & CEPH_FEATURE_OSD_BITWISE_HOBJ_SORT;
+  }
+
   void init_primary_up_acting(
     const vector<int> &newup,
     const vector<int> &newacting,

src/osd/ReplicatedPG.h

@@ -449,6 +449,9 @@ class ReplicatedPG : public PG, public PGBackend::Listener {
   uint64_t min_peer_features() const {
     return get_min_peer_features();
   }
+  bool sort_bitwise() const {
+    return get_sort_bitwise();
+  }
 
   bool transaction_use_tbl() {
     uint64_t min_features = get_min_upacting_features();