server startup (sparse write avoidance doesn't happen until it is finished).
Added mutex to bitset functions, which were already being called from
multiple threads. Rewrote allocation map builder to request file
information in multiple chunks, to avoid uninterruptible wait and dynamic
memory allocation.
If the client cuts off part-way through the write, it should cause an
error, not a fatal. Previously this happened if the open file had a
fiemap, but not if there was no allocation map. This patch fixes that,
along with an associated valgrind error.
O_DIRECT causes problems on (at least) a wheezy VM, and there are mixed
reports about its performance impact. This patch makes it a
compile-time choice which should remain until it's been benchmarked.
