rgw: recover from empty meta.history object

Fixes: http://tracker.ceph.com/issues/21802

Empty meta.history object is problematic, as when reading it when doing
meta log trimming, we'd just initialize it to an empty structure, and
end up asserting because cursor is empty. Cannot just return -ENOENT
here, because it wouldn't solve the issue.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/rgw/rgw_metadata.cc b/src/rgw/rgw_metadata.cc
index 8baa3dd3087..0c6ac0a9224 100644
--- a/src/rgw/rgw_metadata.cc
+++ b/src/rgw/rgw_metadata.cc
@@ -364,6 +364,16 @@ int read_history(RGWRados *store, RGWMetadataLogHistory *state,
   if (ret < 0) {
     return ret;
   }
+  if (bl.length() == 0) {
+    /* bad history object, remove it */
+    rgw_raw_obj obj(pool, oid);
+    ret = store->delete_system_obj(obj);
+    if (ret < 0) {
+      ldout(store->ctx(), 0) << "ERROR: meta history is empty, but cannot remove it (" << cpp_strerror(-ret) << ")" << dendl;
+      return ret;
+    }
+    return -ENOENT;
+  }
   try {
     auto p = bl.begin();
     state->decode(p);