Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

- 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>

- Fix an issue with access permissions to underlying disks used by a gvinum
plex. If the plex is a raid5 plex, and is being written to, parity data might
have to be read from the underlying disks, requiring them to be opened for
reading as well as writing.

MFC after: 1 week

- 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.

Rename the kthread_xxx (e.g. kthread_create()) calls
to kproc_xxx as they actually make whole processes.
Thos makes way for us to add REAL kthread_create() and friends
that actually make theads. it turns out that most of these
calls actually end up being moved back to the thread version
when it's added. but we need to make this cosmetic change first.

I'd LOVE to do this rename in 7.0 so that we can eventually MFC the
new kthread_xxx() calls.

Get rid of the gv_bioq hack in most parts of the I/O path and
use the standard bioq structures.

Make it possible to remove stale, left-over subdisks.

Don't initialize error with ENXIO as we might end up here when
the plex has no more consumers (e.g. orphaning).

Although an object may already be known in the configuration, it's
worker thread may have been destroyed (e.g. during orphaning).

Make sure that objects get back their worker threads when they get a
new geom.

Implement checkparity/rebuildparity.

Give each plex a separate queue where held back bios are put on.
This lowers the CPU usage of the worker thread and prevents a
possible live lock on non-SMP machines.

MFC candidate.

Make it possible to rebuild degraded RAID5 plexes. Note that it is
currently not possible to do this while the volume is mounted.

MFC in: 1 week

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.

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

If we kill the worklist thread of a RAID5 plex we can destroy
the worklist mutex at the same time, so move the mtx_destroy() call
to gv_kill_thread().

Tag all geom classes in the tree with a version number.

Propagate size changes upwards.

Set the access counts of a subdisk correctly when attaching it
to a plex that already has subdisks.

Add a function to clean up RAID5 packets and use it when I/O has
finished or when building the complete packet fails.

Clean up allocated ressources when destroying the main vinum geom.

Handle dead disks in a somewhat sane way.

Add a first version of a GEOMified vinum.