- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

MFC r280757: Remove request sorting from GEOM_MIRROR and GEOM_RAID.

When CPU is not busy, those queues are typically empty. When CPU is busy,
then one more extra sorting is the last thing it needs. If specific device
(HDD) really needs sorting, then it will be done later by CAM.

This supposed to fix livelock reported for mirror of two SSDs, when UFS
fires zillion of BIO_DELETE requests, that totally blocks I/O subsystem by
pointless sorting of requests and responses under single mutex lock.

MFC r280756, r280758: Fix bug on memory allocation error in split method.

While there, use bioq_takefirst() in place where it is convenient.

MFC r279913: Fix couple BIO_DELETE bugs in geom_mirror.

Do not report GEOM::candelete if none of providers support BIO_DELETE.
If consumer still requests BIO_DELETE, report error instead of hanging.

MFC r264142:

Show error code when failing to destroy a mirror on delay

MFC r259634:
Prevent users from deactivating the last component of a mirror.

MFC r259929:
Add an ability to stop gmirror and clear its metadata in one command.
This fixes the problem, when gmirror starts again just after stop.

The problem occurs when gmirror's component has geom label with equal size.
E.g. gpt and gptid have the same size as partition, diskid has the same
size as entire disk. When gmirror's geom has been destroyed, glabel
creates its providers and this initiate retaste.

Now "gmirror destroy" command is available. It destroys geom and also
erases gmirror's metadata.

PR: 184985

MFC r258357:
Add "resize" verb to gmirror(8) and such functionality to geom_mirror(4).
Now it is easy to expand the size of the mirror when all its components
are replaced. Also add g_resize method to geom_mirror class. It will write
updated metadata to new last sector, when parent provider is resized.

MFC Alexander Motin's GEOM direct dispatch work:

r256603:
Introduce new function devstat_end_transaction_bio_bt(), adding new argument
to specify present time. Use this function to move binuptime() out of lock,
substantially reducing lock congestion when slow timecounter is used.

r256606:
Move g_io_deliver() out of the lock, as required for direct dispatch.
Move g_destroy_bio() out too to reduce lock scope even more.

r256607:
Fix passing uninitialized bio_resid argument to g_trace().

r256610:
Add unmapped I/O support to GEOM RAID.

r256830:
Restore BIO_UNMAPPED and BIO_TRANSIENT_MAPPING in biodonne() when unmapping
temporary mapped buffer. That fixes double unmap if biodone() called twice
for the same BIO (but with different done methods).

r256880:
Merge GEOM direct dispatch changes from the projects/camlock branch.

When safety requirements are met, it allows to avoid passing I/O requests
to GEOM g_up/g_down thread, executing them directly in the caller context.
That allows to avoid CPU bottlenecks in g_up/g_down threads, plus avoid
several context switches per I/O.

r259247:
Fix bug introduced at r256607. We have to recalculate bp_resid here since
sizes of original and completed requests may differ due to end of media.

Testing of the stable/10 merge was done by Netflix, but all of the credit
goes to Alexander and iX Systems.

Submitted by: mav
Sponsored by: iX Systems

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

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

Fix the formatting of the error message.

The G_MIRROR_DEBUG() macro already appends a newline. Also, most of the
log messages emitted by gmirror start with an uppercase letter.

Fix a mystery cut-n-paste corruption from the previous commit.

Submitted by: Brenden Fabeny

Mark geom_mirror as capable of unmapped i/o

Obtained from: Netflix
MFC after: 3 days

g_mirror: g_getattr() failure should not be fatal

This allows to use gmirror e.g. on top of ZVOLs.

PR: kern/175323
Submitted by: Alexei.Volkov@softlynx.ru, mav
Reported by: Alexei.Volkov@softlynx.ru
Tested by: Alexei.Volkov@softlynx.ru
Reviewed by: ae, mav, pjd
MFC after: 1 week

Alike to r242314 for GRAID make GMIRROR more aggressive in marking volumes
as clean on shutdown and move that action from shutdown_pre_sync stage to
shutdown_post_sync to avoid extra flapping.

ZFS tends to not close devices on shutdown, that doesn't allow GEOM RAID
to shutdown gracefully. To handle that, mark volume as clean just when
shutdown time comes and there are no active writes.

PR: kern/113957
MFC after: 2 weeks

When synchronizing, include in the config dump amount of
bytes syncronized.
The rationale behind this is the following: for large disks the
percent synchronisation counter ticks too seldom, and monitoring
software (as well as human operator) can't tell whether
synchronisation goes on or one of disks got stuck. On an idle
server one can look into gstat and see whether synchronisation goes
on or not, but on a busy server that won't work. Also, new value
monitored can be differentiated obtaining the synchronisation speed
quite precisely.

Submitted by: Konstantin Kukushkin <dark ramtel.ru>
Reviewed by: pjd

Make geom_mirror more friendly to SSDs. To properly support TRIM,
we need to pass BIO_DELETE requests down to providers that support
it. Also, we need to announce our support for BIO_DELETE to upper
consumer. This requires:

- In g_mirror_start() return true for "GEOM::candelete" request.
- In g_mirror_init_disk() probe below provider for "GEOM::candelete"
attribute, and mark disk with a flag if it does support BIO_DELETE.
- In g_mirror_register_request() distribute BIO_DELETE requests only
to those disks, that do support it.

Note that we announce "GEOM::candelete" as true unconditionally of
whether we have TRIM-capable media down below or not. This is made
intentionally, because upper consumer (usually UFS) requests the
attribite only once at mount time. And if user ever migrates his
mirror from HDDs to SSDs, then he/she would get TRIM working without
remounting filesystem.

Reviewed by: pjd

In g_mirror_regular_request() upon successful delivery treat
BIO_DELETE requests same way as BIO_WRITE removing them from
queue. This fixes panic with BIO_DELETE operations on geom_mirror.

Reviewed by: pjd

Prevent removing of the last active component from a mirror.

PR: kern/154860
Reviewed by: pjd
MFC after: 1 week

Introduce new device flag G_MIRROR_DEVICE_FLAG_TASTING. It should
protect geom from destroying while it is tasting.

PR: kern/154860
Reviewed by: pjd
MFC after: 1 week

Mark all SYSCTL_NODEs static that have no corresponding SYSCTL_DECLs.

The SYSCTL_NODE macro defines a list that stores all child-elements of
that node. If there's no SYSCTL_DECL macro anywhere else, there's no
reason why it shouldn't be static.

Include sys/sbuf.h directly.

Reviewed by: pjd

Implement relaxed comparision for hardcoded provider names to make it
ignore adX/adaY difference in both directions to simplify migration to
the CAM-based ATA or back.

Add some FEATURE macros for various GEOM classes.

No FreeBSD version bump, the userland application to query the features will
be committed last and can serve as an indication of the availablility if
needed.

Sponsored by: Google Summer of Code 2010
Submitted by: kibab
Reviewed by: silence on geom@ during 2 weeks
X-MFC after: to be determined in last commit with code from this project

- Allow to specify value as const pointers.
- Make optional string values always an empty string.

Remove bintime_cmp() function, unused since r200086.

MFC after: 1 week

Move wakeup() out of mutex to reduce contention.

As soon as mirror has no own stripes, report largest stripe of unrerlying
components, hoping others fit, if they are not equal.

Change 'load' balancing mode algorithm:
- Instead of measuring last request execution time for each drive and
choosing one with smallest time, use averaged number of requests, running
on each drive. This information is more accurate and timely. It allows to
distribute load between drives in more even and predictable way.
- For each drive track offset of the last submitted request. If new request
offset matches previous one or close for some drive, prefer that drive.
It allows to significantly speedup simultaneous sequential reads.

PR: kern/113885
Reviewed by: sobomax

Add support for changing providers priority.

Submitted by: Mel Flynn

Revert r190676,190677

The geom and CAM changes for root_hold are the wrong solution for USB design
quirks.

Requested by: scottl

Add a how argument to root_mount_hold() so it can be passed NOWAIT and be called
in situations where sleeping isnt allowed.

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.

Commit 14/14 of sched_lock decomposition.
- Use thread_lock() rather than sched_lock for per-thread scheduling
sychronization.
- Use the per-process spinlock rather than the sched_lock for per-process
scheduling synchronization.

Tested by: kris, current@
Tested on: i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)

Now, that we have gjournal in the tree add possibility to configure
gmirror and graid3 in a way that it is not resynchronized after a
power failure or system crash.
It is safe when gjournal is running on top of gmirror/graid3.

Implement BIO_FLUSH handling by simply passing it down to the components.

Sponsored by: home.pl

Fix synchronization in gmirror and graid3 which I broken. Synchronization
request can still have bio_to set to sc_provider (this is READ part of a
synchronization request) and in this case g_{mirror,raid3}_sync() wasn't
called as it should be.

MFC after: 1 week

move created/detected/activated under debug level 1 to quiet the common case..

add count of active and total components to the launched line so you can
see at a glance if your mirror/raid3 is complete...

now:
GEOM_MIRROR: Device mirror/sam launched (2/2).

Reviewed by: pjd

Not only a request from us can be passed to g_{mirror,raid3}_worker()
function, but also a request to us, in which case checking bio_cflags
is wrong, because the class above us is controling it, not we.

MFC after: 1 week

Commit the results of the typo hunt by Darren Pilgrim.
This change affects documentation and comments only,
no real code involved.

PR: misc/101245
Submitted by: Darren Pilgrim <darren pilgrim bitfreak org>
Tested by: md5(1)
MFC after: 1 week

Don't use f-word in comments. We are gentlemans.

Pointed out by: Maciej Sobczak

Always allow to specify components with /dev/ prefix.

MFC after: 3 days

Use proper defines instead of magic values.

MFC after: 1 week

Allow to close access even if device is already destroyed.

Reported by: Ulrich Spoerlein <uspoerlein@gmail.com>
PR: kern/98093
MFC after: 1 week

- Remove dead code.
- Comment possible event miss, which isn't critical, but probably can be
fixed by replacing the event lock usage with the queue lock.

MFC after: 2 weeks

Be sure to not destroy device twice. This is not possible in theory, but
with this change there is even no theoretical race.

MFC after: 2 weeks

Introduce and use delayed-destruction functionality from a pre-sync hook,
which means that devices will be destroyed on last close.

This fixes destruction order problems when, eg. RAID3 array is build on
top of RAID1 arrays.

Requested, reviewed and tested by: ru
MFC after: 2 weeks

- 'ndisks' variable is not boolean, so compare it with a value.
- Keep conditions order consistent with the comment above.

MFC after: 3 days

Update copyright for 2006.

kern.geom.mirror.sync_requests=2 seems to be a better default - it still
keeps disks very busy, but makes system much more responsive.

While here, kill extra space.

Fix build on 64-bit platforms.

- Speed up synchronization process by using configurable number of I/O
requests in parallel.
+ Add kern.geom.mirror.sync_requests tunable which defines how many parallel
I/O requests should be used.
+ Retire kern.geom.mirror.reqs_per_sync and kern.geom.mirror.syncs_per_sec
sysctls.
- Fix race between regular and synchronization requests.
- Reimplement mirror's data synchronization - do not use the topology lock
for this purpose, as it may case deadlocks.
- Stop synchronization from pre-sync hook.
- Fix some other minor issues.

MFC after: 3 days

When inserting a new component md_provsize metadata field wasn't set, which
means that old problem was triggered (when two providers end at the same
offset, eg. ad0 and ad0s1 and the wrong was is picked up by gmirror/graid3).

Reported by: Michal Suszko <dry@dry.pl>
MFC after: 3 days

Allow to dump kernel to gmirror providers.
Some conditions have to be met to make it work properly. This will be
described in the manual page.

MFC after: 3 days

On component state change to ACTIVE don't forget to update metadata.

MFC after: 3 days

Use time_uptime instead of time_second, as the latter may go backwards.

Suggested by: ru
MFC after: 3 days

- Add kern.geom.mirror.disconnect_on_failure sysctl/tunnable (default to 1
to preserve currect behaviour). When set to 0, components are not
disconnected - gmirror will try to still use them (only first error will
be logged). This is helpful when we have two broken components, but in
different places, so actually all data is available.
Such buggy component will be visible in 'gmirror list' output with flag
BROKEN.
- Never disconnect the last valid component. If we detect errors there we
will just pass them up. This wasn't reasonable to deny access to the
whole provider because of one broken sector.

Prodded by: ru
MFC after: 3 days

Mark array as CLEAN when there are no write requests in
kern.geom.mirror.idletime seconds. Write, not any requests.
Mark array as clean immediatelly on last write close.

Prodded by: ru
MFC after: 3 days

Remove trailing spaces.

Remove dead code.

Found by: Coverity Prevent(tm)
Coverity ID: CID104
MFC after: 3 days

Check for g_read_data(9) errors properly:

o The only indication of error condition is NULL value returned by
the function;

o value pointed to by error argument is undefined in the case when
operation completes successfully.

Discussed with: phk

Normalize a significant number of kernel malloc type names:

- Prefer '_' to ' ', as it results in more easily parsed results in
memory monitoring tools such as vmstat.

- Remove punctuation that is incompatible with using memory type names
as file names, such as '/' characters.

- Disambiguate some collisions by adding subsystem prefixes to some
memory types.

- Generally prefer lower case to upper case.

- If the same type is defined in multiple architecture directories,
attempt to use the same name in additional cases.

Not all instances were caught in this change, so more work is required to
finish this conversion. Similar changes are required for UMA zone names.

After provider creation!!

- Call root_mount_rel() when provider IS created, not earlier.
This should close the race observed by Daniel Eriksson.
- Remove redundant wakeup().

Add some debug code to diagnose root-on-mirror problems with recent -current.

Reported by: Daniel Eriksson

Add KASSERT() to be sure there is an active component.

Suggested by: Coverity Prevent analysis tool

Fix provider's size check for 'insert' command.
Before this fix one was able to insert one sector too small provider.

MFC after: 3 days

Remove the hack which allowed to use gmirror for root file system,
use root_mount KPI instead.

Make the code more obvious - when an error occurs in g_mirror_connect_disk(),
detach and destroy consumer before returning.

Check for return values.

Submitted by: sam
Found by: Coverity Prevent analysis tool

- Add md_provsize field to metadata, which will help with
shared-last-sector problem.
After this change, even if there is more than one provider with the same
last sector, the proper one will be chosen based on its size.
It still doesn't fix the 'c' partition problem (when da0s1 can be confused
with da0s1c) and situation when 'a' partition starts at offset 0
(then da0s1a can be confused with da0s1 and da0s1c). One can use '-h'
option there, when creating device or avoid sharing last sector.
Actually, when providers share the same last sector and their size is equal,
they provide exactly the same data, so the name (da0s1, da0s1a, da0s1c)
isn't important at all.
- Provide backward compatibility.
- Update copyright's year.

MFC after: 1 week

Update copyright in files changed this year.

Increase default synchronization speed.

MFC after: 3 days

Spoiling is now not possible, because we keep consumers open for writing
all the time. Remove unused code then.

MFC after: 4 days

Fix 'rebuild' command (we ignore retaste event now, so don't relay on it).

Stop explicitly touching td_base_pri outside of the scheduler and simply
set a thread's priority via sched_prio() when that is the desired action.
The schedulers will start managing td_base_pri internally shortly.

Update disk->d_genid field when increasing sc->sc_genid.

- Add genid field to the metadata which will allow to improve reliability a bit.
After this change, when component is disconnected because of an I/O error,
it will not be connected and synchronized automatically, it will be logged
as broken and skipped. Autosynchronization can occur, when component is
disconnected (on orphan event) and connected again - there were no I/O
error, so there is no need to not connected the component, but when there were
writes while it wasn't connected, it will be synchronized.
This fix cases, when component is disconnected because of I/O error and can be
connected again and again.
- Bump version number.
- Add version change history.
- Implement backward compatibility mechanism. After this change when metadata in
old version is detected, it is automatically upgraded to the new (current)
version.

Now, when force device destruction is done on shutdown, hide warning,
that device cannot be destroyed immediately, under debug=1.

Suggested by: simon

This should not be permitted, but some GEOM classes held the topology lock
while doing g_(read|write)_data() (e.g. BSD). This can cause a deadlock
in MIRROR class. Not sure if this is safe to drop the topology lock in BSD
class, so change the code in MIRROR class to avoid this deadlock.

Remove unused variables.

- Argument 'flags' in g_mirror_destroy_consumer() function is unsed -
mark it as such.
- Before closing consumer check if it is open. It can be closed here
when g_mirror_connect_disk() fails on g_access().

Some major cleanups.

Keeping consumers open when device is closed is very hard. We need to
open consumers sometimes to update metadata, etc.
Many hacks was introduced in the past to made it possible. You cannot
be sure that you can open consumer for writing always, even if you think
it should be allowed. If one of the mirror components is for example da0
and you try to open it, you can get EPERM when da0s1 is opened for reading
(because BSD class opens consumers (da0) with an extra 'e' bit set).
Waiting for the events queue to be empty may do the trick, but it makes
code much uglier (as you cannot always call g_waitidle()), it doesn't
solve all edge cases and it can introduce deadlocks if there are events
in the queue that wait for gmirror.

I removed those hacks. Now all consumers are open r1w1e1 always, even if
device is closed. Maybe it is less clean from GEOM perspective, but simpify
code a lot and make it much more reliable.
The only issue was retaste event which is sent when we close consumers
opened for writing. I ignore retaste event by not detaching consumer
immediately (so retaste event is not send to my class) and sending event
right after it to detach and destroy consumer.

Don't quit on first failure, just skip failures.

Before trying to update metadata (so open consumer for writing), be sure
that the events queue is empty. In other case we're able to hit the race
where for example da0s1 is tasted by some other class, which means that
da0 is open with exclusive bit set, which means that we can't open da0
for writing if it is our component.

Reported by: Attila Nagy <bra@fsn.hu> (and somebody else sometime ago,
but I cannot find who it was)

Don't rely on DIRTY flag to be sure that consumer if open, because
DIRTY flag can be removed in idle process. Use consumer's acw field
instead to avoid opening consumer twice.

Drop Giant lock before grabbing the topology lock.

If device is marked as beeing destroyed, deny all access requests.

Don't forget to make sure that there are no not-finished requests before
marking components as clean.

Pointed out by: scottl

Use shutdown hooks to mark mirrors as clean after all file systems are
unmounted.

Suggested by: scottl

Remove unused #include.

- Add a sysctl kern.geom.mirror.idletime, so one can specify after how many
seconds of idling, DRITY flags are removed.
- If mirror is in idle state or is not open for writing, sleep without
timeout when waiting for I/O requests.
- Don't use atomic operations, for now sysctls are protected by Giant.
- Update debugs.

MFp4:
- Fix for good (I hope) force-stopping mirrors and some filure cases
(e.g. the last good component dies when synchronization is in progress).
Don't use ->nstart/->nend consumer's fields, as this could be racy,
because those fields are used in g_down/g_up, use ->index consumer's
field instead for tracking number of not finished requests.

Reported by: marcel

- After 5 seconds of idle time (this should be configurable) mark all
dirty providers as clean, so when mirror is not used in 5 seconds
and there will be power failure, no synchronization on boot is needed.

Idea from: sorry, I can't find who suggested this

- When there are no ACTIVE components and no NEW components destroy whole
mirror, not only provider.

- Fix one debug to show information about I/O request, before we change
its command.

Ehh. Introduce a hack: Wait for 3 seconds, so GEOM is able to give us
providers for tasting. Before this hack, race below is possible:
SI_SUB_RAID (no not-fully-configured geoms, so don't block)
GEOM tasting (now geoms are created)
SI_SUB_MOUNT_ROOT (if root file system is placed on a mirror, it is
possible that this mirror is not fully configured yet)
There is a lot of work to do to avoid such hacks and I need a working
solution before 5.3, sorry.

Reported by: John Hay <jhay@icomtek.csir.co.za>

Be sure to always return 0 for negative access requests.

Reported by: Maciej Kucharz <qk@comp.waw.pl>

Geoms without softc are geoms which are initialized, so wait for them.

Look out for geoms without softc.

Reported by: tegge

Before root file system is mounted, wait for mirrors in degraded state.

Just use MAXPHYS as maximum I/O request size, instead of using my own
#define for this purpose.
No functional change.

Minor, but very important condition fix. The current one can never be true.

Decrease kern.geom.mirror.timeout to 4, so it is smaller than
vfs.root.mountdelay by default.

Forgot to commit addition of ds_resync field.

Avoid race while synchronizing components. It is very hard to bump into,
but it is possible:
1. Read data from good component for synchronization.
2. Write data to the same area.
3. Write synchronization data, which are now stale.

Found by: tegge

Simplify code a bit.

This is not needed anymore, it is forced in GEOM now.
Actually, it can even cause some problems, because GEOM requires sectorsize
to be more than 0 on first access, not on provider creation, so we can skip
valid providers by doing this check here.

Reported by: Divacky Roman <xdivac02@stud.fit.vutbr.cz>
Sven Willenberger <sven@dmv.com>

Show current status of mirror device directly.

Suggested by: Krzysztof Ciep³ucha <kris@home.pl>

Allow to configure debug level from /boot/loader.conf.

GCC, ehh.

Skip providers with not defined sector size.

Reported by: kuriyama

Allow to set kern.geom.mirror.timeout from /boot/loader.conf.

We really don't want to receive spoil event for synchroniztion consumers.

Bump synchronization ID if we are sure, that we have ACTIVE components.

Avoid code duplication by introducing g_mirror_write_metadata() function,
which is used now by g_mirror_clear_metadata() function and
g_mirror_update_metadata() function.

MFp4: Simplify code a bit:
- Remove kern.geom.mirror.sync_block_size sysctl. It is quite obvious that we
want to use the biggest size possible.
- Do not use UMA zone for sync data allocations. There could be only one
synchronization request per synchronized disk at a time, so allocate memory
for one request on whole synchronization process related to one disk.

Tested by synchronizing one component (out of three) and by synchronizing
two components (out of three) in parallel.

Actually, HARDCODED flag isn't stored in metadata, so don't bother
dumping it.

- Fix typo.
- Dump HARDCODED flag.

Try harder to not panic on 'stop -f'.
After the commit, this command should be really safe to use.

- Recognize HARDCODED flag when dumping consumer configuration.
- Improve code readabilty a bit.

Forgot to commit those: introduce hardcoded provider functionality,
which allow to store provider's name in the metadata and avoid
problems when few providers share the same last sector.

- Introduce option for hardcoding providers' names into metadata.
It allows to fix problems when last provider's sector is shared between few
providers.
- Bump version number for CONCAT and STRIPE and add code for backward
compatibility.
- Do not bump version number of MIRROR, as it wasn't officially introduced yet.
Even if someone started to play with it, there is no big deal, because
wrong MD5 sum of metadata will deny those providers.
- Update manual pages.
- Add version history to g_(stripe|concat).h files.

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

Don't use 'bp' after its destruction!

Simplify a bit - we could use 'sc' here as it was initialized properly.

- Add two fields to bio structure: 'bio_cflags' which can be used by
consumer and 'bio_pflags' which can be used by provider.
- Remove BIO_FLAG1 and BIO_FLAG2 flags. From now on new fields should be
used for internal flags.
- Update g_bio(9) manual page.
- Update some comments.
- Update GEOM_MIRROR, which was the only one using BIO_FLAGs.

Idea from: phk
Reviewed by: phk

- Add "prefer" balance algorithm. When used, only disk with the biggest
priority will be used for reading.
- Bump version number.

MFp4: We don't really need g_mirror_free_disk() function.

Fix comment.

Typo.

- Launch main provider when there are no more disks in NEW state.
- Log syncid bump at debug level 1.

If there are no valid components after the timeout, just destroy device.
There is probably nothing to wait for.

Handle spoil event in dedicated function: g_mirror_spoiled().
The different between the new function and g_mirror_orphan() (which was
used previously) is that syncid is bumped immediately, instead of on
first write, because when consumer was spoiled, it means, that its
provider was opened for writing, so we can't trust that its data
will be valid when it will be connected again.

Remove unused field.

Destroy synchronization geom immediately. This should fix unloading without
stopping all mirrors.

Add '-p' option for 'insert' command which allows to specify priority
of the new component.
Version number wasn't bumped (it should be), because I think there are
no geom_mirror users yet.

- Check if 'slice' argument was given.
- Check if disk isn't already the mirror component.

Dump correct field.

Add GEOM_MIRROR class which provide RAID1 functionality and has many useful
features. The gmirror(8) utility should be used for control of this class.
There is no manual page yet, but I'm working on it with keramida@.

Many useful tests provided by: simon (thank you!)
Some ideas from: scottl, simon, phk