MFC r356138: Reimplement gvinum orphanization.

gvinum was the only GEOM class, using consumer nstart/nend fields. Making
it do its own accounting for orphanization purposes allows in perspective
to remove burden of that expensive for SMP accounting from GEOM.

Also the previous implementation spinned in a tight event loop, waiting
for all active BIOs to complete, while the new one knows exactly when it
is possible to close the consumer.

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

- Don't return EAGAIN from gv_unload(). It was used to work around the
deadlock fixed in r207671.
- Wait for worker process to exit at class unload. The worker process
was not guaranteed to exit before the linker unloaded the module.
- Use 0 as the worker process exit status instead of ENXIO and style
the NOTREACHED comment.

Reviewed by: lulf
X-MFC after: r207671

- Split up the BIO queue into a queue for new and one for completed requests.
This is necessary for two reasons:
1) In order to avoid collisions with the use of a BIOs flags set by a consumer
or a provider
2) Because GV_BIO_DONE was used to mark a BIO as done, not enough flags was
available, so the consumer flags of a BIO had to be misused in order to
support enough flags. The new queue makes it possible to recycle the
GV_BIO_DONE flag into GV_BIO_GROW.
As a consequence, gvinum will now work with any other GEOM class under it or
on top of it.

- Use bio_pflags for storing internal flags on downgoing BIOs, as the requests
appear to come from a consumer of a gvinum volume. Use bio_cflags only for
cloned BIOs.
- Move gv_post_bio to be used internally for maintenance requests.
- Remove some cases where flags where set without need.

PR: kern/133604

- Split the queue mutex into one for the event queue and one for the BIO queue,
as they do not really relate and to prepare for an additional queue to be
covered by the BIO queue mutex.
- Implement wrappers for fetching the next element from the event queue as well
as for putting a new element into the BIO queue.

Import the gvinum work that have been done during and after Summer of Code 2007.
The work have been under testing and fixing since then, and it is mature enough
to be put into HEAD for further testing.

A lot have changed in this time, and here are the most important:
- Gvinum now uses one single workerthread instead of one thread for each
volume and each plex. The reason for this is that the previous scheme was
very complex, and was the cause of many of the bugs discovered in gvinum.
Instead, gvinum now uses one worker thread with an event queue, quite
similar to what used in gmirror.
- The rebuild/grow/initialize/parity check routines no longer runs in
separate threads, but are run as regular I/O requests with special flags.
This made it easier to support mounted growing and parity rebuild.
- Support for growing striped and raid5-plexes, meaning that one can extend the
volumes for these plex types in addition to the concat type. Also works while
the volume is mounted.
- Implementation of many of the missing commands from the old vinum:
attach/detach, start (was partially implemented), stop (was partially
implemented), concat, mirror, stripe, raid5 (shortcuts for creating volumes
with one plex of these organizations).
- The parity check and rebuild no longer goes between userland/kernel, meaning
that the gvinum command will not stay and wait forever for the rebuild to
finish. You can instead watch the status with the list command.
- Many problems with gvinum have been reported since 5.x, and some has been hard
to fix due to the complicated architecture. Hopefully, it should be more
stable and better handle edge cases that previously made gvinum crash.
- Failed drives no longer disappears entirely, but now leave behind a dummy
drive that makes sure the original state is not forgotten in case the system
is rebooted between drive failures/swaps.
- Update manpage to reflect new commands and extend it with some examples.

Sponsored by: Google Summer of Code 2007
Mentored by: le
Tested by: Rick C. Petty <rick-freebsd2008 -at- kiwi-computer.com>

- Import macros used in gmirror for printing gvinum debug messages and making
the output more standardized.
- Add a sysctl to set the verbosity of the debug messages.
- While there, fixup typos and wording in the messages.

- Make gvinum header on-disk structure consistent on all platforms by storing
the gvinum header in fields of fixed size and in a big endian byte order
rather than the size and byte order of the actual platform.

Note that the change is backwards compatible with the old gvinum configuration
format, but will save the configuration in the new format when the 'saveconfig'
command is executed.

Submitted by: Rick C. Petty <rick-freebsd -at- kiwi-computer.com>

-) Correct sdcount for a plex when removing or adding subdisks.
-) Set correct sizes for plexes and volumes a subdisk has been removed.

Submitted by: Ulf Lilleengen <lulf_AT_freebsd.org>

Protect from creating striped and RAID5 plexes with unequally sized
subdisks.

Implement the 'resetconfig' command.

PR: kern/94835
Submitted by: Ulf Lilleengen <lulf@stud.ntnu.no>

Finally bring in what was produced during Google SoC 2005:

Add functions to rename objects and to move a subdisk from one drive
to another.

Obtained from: Chris Jones <chris.jones@ualberta.ca>
Sponsored by: Google Summer of Code 2005
MFC in: 1 week

Implement 'setstate' to allow setting the state of drives and subdisks
for debugging and emergency purposes.

Implement checkparity/rebuildparity.

Share gv_roughlength() between kernel and userland, as we will need it
there later.

Re-vamp how I/O is handled in volumes and plexes.

Analogous to the drive level, give each volume and plex a worker thread
that picks up and processes incoming and completed BIOs.

This should fix the data corruption issues that have come up a few
weeks ago and improve performance, especially of RAID5 plexes.

The volume level needs a little work, though.

Give the DRIVE geom a worker thread that picks up incoming bios,
sends them down, and takes care of the finished bios. This makes it
easier to handle I/O errors at drive level.

Rename gv_kill_thread() to gv_kill_plex_thread(), since there are more
threads to come.

Move config_new_drive() to the correct place and rename it to
gv_config_new_drive().

Propagate size changes upwards.

Add a first version of a GEOMified vinum.