netlink-socket: Simplify use of transactions and dumps.

This disentangles "struct nl_dump" from "struct nl_sock", clearing the way
to make the use of either one thread-safe in an obviously correct manner.

Signed-off-by: Ben Pfaff <blp@nicira.com>
netlink-socket: Make thread-safe.

The uses of vlog in this module are not thread-safe, because vlog itself
is not yet thread-safe.

Signed-off-by: Ben Pfaff <blp@nicira.com>
system-stats: Move into separate thread.

Signed-off-by: Ben Pfaff <blp@nicira.com>
util: New macros ROUND_UP_POW2, ROUND_DOWN_POW2.

Signed-off-by: Ben Pfaff <blp@nicira.com>
async-append: New library to allow asynchronous appending to a log file.

This will be hooked into the vlog library in an upcoming commit.

Signed-off-by: Ben Pfaff <blp@nicira.com>
vlog: Use async I/O.

Signed-off-by: Ben Pfaff <blp@nicira.com>
vlog: Make thread-safe.

Signed-off-by: Ben Pfaff <blp@nicira.com>