MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Make hastctl list command output current queue sizes.

Reviewed by: pjd
MFC after: 1 month

Make hastctl(1) ('list' command) output a worker pid.

Reviewed by: pjd
MFC after: 3 days

Add i/o error counters to hastd(8) and make hastctl(8) display
them. This may be useful for detecting problems with HAST disks.

Discussed with and reviewed by: pjd
MFC after: 1 week

For functions that return -1 on failure check exactly for -1 and not for
any negative number.

MFC after: 3 days

Remove redundant setting of the error variable.

Found by: Clang Static Analyzer
MFC after: 1 week

Prefer PJDLOG_ASSERT() and PJDLOG_ABORT() over assert() and abort().
pjdlog versions will log problem to syslog when application is running in
background.

MFC after: 3 days

Remove useless initialization.

Approved by: pjd (mentor)
MFC after: 3 days

Keep statistics on number of BIO_READ, BIO_WRITE, BIO_DELETE and BIO_FLUSH
requests as well as number of activemap updates.

Number of BIO_WRITEs and activemap updates are especially interesting, because
if those two are too close to each other, it means that your workload needs
bigger number of dirty extents. Activemap should be updated as rarely as
possible.

MFC after: 1 week

Rename HASTCTL_ defines, which are used for conversion between main
hastd process and workers, remove unused one and set different range
of numbers. This is done in order not to confuse them with HASTCTL_CMD
defines, used for conversation between hastctl and hastd, and to avoid
bugs like the one fixed in in r221075.

Approved by: pjd (mentor)
MFC after: 1 week

For conversation between hastctl and hastd we should use HASTCTL_CMD
defines.

Approved by: pjd (mentor)
MFC after: 1 week

Remove stale comment. Yes, it is valid to set role back to init.

MFC after: 1 week

In hast.conf we define the other node's address in 'remote' variable.
This way we know how to connect to secondary node when we are primary.
The same variable is used by the secondary node - it only accepts
connections from the address stored in 'remote' variable.
In cluster configurations it is common that each node has its individual
IP address and there is one addtional shared IP address which is assigned
to primary node. It seems it is possible that if the shared IP address is
from the same network as the individual IP address it might be choosen by
the kernel as a source address for connection with the secondary node.
Such connection will be rejected by secondary, as it doesn't come from
primary node individual IP.

Add 'source' variable that allows to specify source IP address we want to
bind to before connecting to the secondary node.

MFC after: 1 week

Allow to compress on-the-wire data using two algorithms:
- HOLE - it simply turns all-zero blocks into few bytes header;
it is extremely fast, so it is turned on by default;
it is mostly intended to speed up initial synchronization
where we expect many zeros;
- LZF - very fast algorithm by Marc Alexander Lehmann, which shows
very decent compression ratio and has BSD license.

MFC after: 2 weeks

Allow to checksum on-the-wire data using either CRC32 or SHA256.

MFC after: 2 weeks

Setup another socketpair between parent and child, so that primary sandboxed
worker can ask the main privileged process to connect in worker's behalf
and then we can migrate descriptor using this socketpair to worker.
This is not really needed now, but will be needed once we start to use
capsicum for sandboxing.

MFC after: 1 week

Remember created control connection so on fork(2) we can close it in child.

Found with: procstat(1)
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

Add missing logs.

MFC after: 1 week

Use int16 for error.

MFC after: 1 week

We close the event socketpair early in the mainloop to prevent spaming with
error messages, so when we clean up after child process, we have to check if
the event socketpair is still there.

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

Fix descriptor leaks: when child exits, we have to close control and event
socket pairs. We did that only in one case out of three.

MFC after: 3 days

If we are unable to receive control message is most likely because the main
process died. Instead of entering infinite loop, terminate.

MFC after: 3 days

Sort includes.

MFC after: 3 days

- Call hook on role change.
- Document new event.

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

Make control_set_role() more public. We will need it soon.

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