If a crash occurs during flushing a redirect-write it may happen so that
the disk contains both old and new metadata entries. This is OK, but prior
to 0.8.0 after this situation OSDs started without problem, but then they
crashed after some more overwrites with a "tried to overwrite non-zero
metadata entry" error. 0.8.0 introduced a change that was intended to fix
this situation, but rather than fixing it it prevented OSDs from starting,
now because of a "big_write journal_entry was allocated over another object"
error... :-)
This change finally fixes the original issue.
Followup to 54ef2c389f
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
Vitaliy Filippov