Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Add function to assert that the only descriptors we have open are the ones
we expect to be open. Also assert that they point at expected type.

Because openlog(3) API is unable to tell us descriptor number it is using, we
have to close syslog socket, remember assert message in local buffer and if we
fail on assertion, reopen syslog socket and log the message.

MFC after: 1 week

Add function to close all unneeded descriptors after fork(2).

MFC after: 1 week

Don't open configuration file from worker process. Handle SIGHUP in the
master process only and pass changes to the worker processes over control
socket. This removes access to global namespace in preparation for capsicum
sandboxing.

MFC after: 2 weeks

Switch to sigprocmask(2) API also in the main process and secondary process.
This way the primary process inherits signal mask from the main process,
which fixes a race where signal is delivered to the primary process before
configuring signal mask.

Reported by: Mikolaj Golub <to.my.trociny@gmail.com>
MFC after: 3 days

Allow to execute specified program on various HAST events.

MFC after: 2 weeks
Obtained from: Wheel Systems Sp. z o.o. http://www.wheelsystems.com

Implement configuration reload on SIGHUP. This includes:
- Load added resources.
- Stop and forget removed resources.
- Update modified resources in least intrusive way, ie. don't touch
/dev/hast/<name> unless path to local component or provider name were
modified.

Obtained from: Wheel Systems Sp. z o.o. http://www.wheelsystems.com
MFC after: 1 month

Please welcome HAST - Highly Avalable Storage.

HAST allows to transparently store data on two physically separated machines
connected over the TCP/IP network. HAST works in Primary-Secondary
(Master-Backup, Master-Slave) configuration, which means that only one of the
cluster nodes can be active at any given time. Only Primary node is able to
handle I/O requests to HAST-managed devices. Currently HAST is limited to two
cluster nodes in total.

HAST operates on block level - it provides disk-like devices in /dev/hast/
directory for use by file systems and/or applications. Working on block level
makes it transparent for file systems and applications. There in no difference
between using HAST-provided device and raw disk, partition, etc. All of them
are just regular GEOM providers in FreeBSD.

For more information please consult hastd(8), hastctl(8) and hast.conf(5)
manual pages, as well as http://wiki.FreeBSD.org/HAST.

Sponsored by: FreeBSD Foundation
Sponsored by: OMCnet Internet Service GmbH
Sponsored by: TransIP BV