Ceph » Linux kernel client

Josh suggested we could pass along the data to be written
along with the STAT op sent to the osd for a target object
for a write to a layered image.

If the stat succeeds, the write would then be done. If the
stat failed, the write would not be performed.

Doing this saves a round trip latency for objects that
already exist, at the expense of the bandwidth consumption
of sending the data twice for those that do not.