Build problems fixed:
- void* pointer arithmetic which is a GNU extension (works as byte*)
- "variable size object may not be initialized" which is OK under GCC
- nullptr_t related error in json11 (it lacks 'operator <' in clang)
Warnings fixed:
- empty nested struct initializer { 0 } replaced by {}
- removed several unused lambda captures
From now on, reads will return the server-side object version numbers
and writes and deletes will have an additional "version" parameter
which, if set to a non-zero value, will be atomically compared with
the current version of the object plus 1 and the modification will
fail if it doesn't match.
This feature opens the road to correct online flattening of snapshot
layers and other interesting things.
- Write operations could be 'stabilized' and previous versions could be
purged from OSDs before the removal of version_override and following
reads could potentially hit different version in EC pools
- Object was marked clean after completing the delete during recovery, so
reads could in theory hit a deleted version and return nothing
Previously OSDs could commit deletes before writes during recovery or rebalance
in the "lazy fsync" (immediate_commit=off) mode which could result in lost objects