Ceph

Motivation:
cls_log and cls_rgw are currently implementing trim by listing 1000 entries with cls_cxx_map_get_vals(), then making a separate call to cls_cxx_map_remove_key() for each key. Although trim isn't generally a bottleneck, this has been observed to take longer than the osd_op_thread_suicide_timeout when omaps are very large.

Proposal:
A new cls_cxx_map_remove_key_range() for the cls api, along with the corresponding operation in librados.