osd/osd_types: skip encoding newer object_info_t fields if they are u…

…nused

This reduces the size of the encoded object_info_t in most cases,
enough to get us under the 255 byte limit for a single inline
xattr in XFS.

Note that we lose the local_mtime, but that this field is only
important for objects in the cache pool.

Note that we drop the unconditional clearing of the digest flags if the
encoding was old; this was not strictly correct anyway.  And now that we
may encode the old way with FLAG_OMAP_DIGEST, we need to leave it set (and
force the value to -1).

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

src/osd/osd_types.cc

@@ -4225,7 +4225,18 @@ void object_info_t::encode(bufferlist& bl) const
        ++i) {
     old_watchers.insert(make_pair(i->first.second, i->second));
   }
-  ENCODE_START(15, 8, bl);
+
+  // kludge to reduce xattr size for most rbd objects
+  int ev = 15;
+  if ((flags & ~0xff) == 0 &&  // no flags outside low 8 bits set
+      (!(flags & FLAG_OMAP) || !(flags & FLAG_OMAP_DIGEST)) &&
+      !(flags & FLAG_DATA_DIGEST) &&
+      watchers.empty()) {      // no watchers
+    // note: we dropped local_mtime too, even though it may have been used.
+    ev = 10;
+  }
+
+  ENCODE_START(ev, 8, bl);
   ::encode(soid, bl);
   ::encode(myoloc, bl);	//Retained for compatibility
   ::encode((__u32)0, bl); // was category, no longer used
@@ -4240,19 +4251,33 @@ void object_info_t::encode(bufferlist& bl) const
     ::encode(snaps, bl);
   ::encode(truncate_seq, bl);
   ::encode(truncate_size, bl);
-  ::encode(is_lost(), bl);
+  {
+    __u8 lo = is_lost();
+    if (ev < 13) {
+      lo = flags;   // all flags fit in 8 bits!
+    }
+    ::encode(lo, bl);
+  }
   ::encode(old_watchers, bl);
   /* shenanigans to avoid breaking backwards compatibility in the disk format.
    * When we can, switch this out for simply putting the version_t on disk. */
   eversion_t user_eversion(0, user_version);
   ::encode(user_eversion, bl);
   ::encode(test_flag(FLAG_USES_TMAP), bl);
-  ::encode(watchers, bl);
-  __u32 _flags = flags;
-  ::encode(_flags, bl);
-  ::encode(local_mtime, bl);
-  ::encode(data_digest, bl);
-  ::encode(omap_digest, bl);
+  if (ev >= 11) {
+    ::encode(watchers, bl);
+  }
+  if (ev >= 13) {
+    __u32 _flags = flags;
+    ::encode(_flags, bl);
+  }
+  if (ev >= 14) {
+    ::encode(local_mtime, bl);
+  }
+  if (ev >= 15) {
+    ::encode(data_digest, bl);
+    ::encode(omap_digest, bl);
+  }
   ENCODE_FINISH(bl);
 }
 
@@ -4327,8 +4352,6 @@ void object_info_t::decode(bufferlist::iterator& bl)
     ::decode(omap_digest, bl);
   } else {
     data_digest = omap_digest = -1;
-    clear_flag(FLAG_DATA_DIGEST);
-    clear_flag(FLAG_OMAP_DIGEST);
   }
   DECODE_FINISH(bl);
 }