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

sys/geom: spelling fixes.

These affect debugging messages.

MFC after: 2 weeks

sys: extend use of the howmany() macro when available.

We have a howmany() macro in the <sys/param.h> header that is
convenient to re-use as it makes things easier to read.

Reduce number of opens by REOM RAID during provider taste.

Instead opening/closing provider by each of metadata classes, do it only
once in core code. Since for SCSI disks open/close means sending some
SCSI commands to the device, this change reduces taste time.

MFC after: 2 weeks
Sponsored by: iXsystems, Inc.

Fix wrong sizes used to access PD_Type and PD_State DDF metadata fields.

This caused incorrect behavior of arrays with big-endian DDF metadata.
Little-endian (like used by Adaptec controllers) should not be harmed.
Add workaround should be enough to manage compatibility.

MFC after: 2 weeks

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.

The defined now safety requirements are:
- caller should not hold any locks and should be reenterable;
- callee should not depend on GEOM dual-threaded concurency semantics;
- on the way down, if request is unmapped while callee doesn't support it,
the context should be sleepable;
- kernel thread stack usage should be below 50%.

To keep compatibility with GEOM classes not meeting above requirements
new provider and consumer flags added:
- G_CF_DIRECT_SEND -- consumer code meets caller requirements (request);
- G_CF_DIRECT_RECEIVE -- consumer code meets callee requirements (done);
- G_PF_DIRECT_SEND -- provider code meets caller requirements (done);
- G_PF_DIRECT_RECEIVE -- provider code meets callee requirements (request).
Capable GEOM class can set them, allowing direct dispatch in cases where
it is safe. If any of requirements are not met, request is queued to
g_up or g_down thread same as before.

Such GEOM classes were reviewed and updated to support direct dispatch:
CONCAT, DEV, DISK, GATE, MD, MIRROR, MULTIPATH, NOP, PART, RAID, STRIPE,
VFS, ZERO, ZFS::VDEV, ZFS::ZVOL, all classes based on g_slice KPI (LABEL,
MAP, FLASHMAP, etc).

To declare direct completion capability disk(9) KPI got new flag equivalent
to G_PF_DIRECT_SEND -- DISKFLAG_DIRECT_COMPLETION. da(4) and ada(4) disk
drivers got it set now thanks to earlier CAM locking work.

This change more then twice increases peak block storage performance on
systems with manu CPUs, together with earlier CAM locking changes reaching
more then 1 million IOPS (512 byte raw reads from 16 SATA SSDs on 4 HBAs to
256 user-level threads).

Sponsored by: iXsystems, Inc.
MFC after: 2 months

Fix vdc->Secondary_Element_Count metadata field access from 16 to 8 bit.
In some cases it could cause kernel panic during failed drive replacement.

Reported by: trasz
MFC after: 1 week

Fix panic when Secondary_Element_Count == 1 and Secondary_Element_Seq
is not set (255).

Reported by: sbruno
MFC after: 1 week

Add basic BIO_DELETE support to GEOM RAID class for all RAID levels.

If at least one subdisk in the volume supports it, BIO_DELETE requests
will be propagated down. Unfortunatelly, for RAID levels with redundancy
unmapped blocks will be mapped back during first rebuild/resync process.

Sponsored by: iXsystems, Inc.
MFC after: 1 month

Make graid command line a bit more friendly by allowing volume name or
provider name to be specified instead of geom name (first argument in all
subcommands except label). In most cases there is only one array used
any way, so it is not really useful to make user type ugly geom names like
Intel-f0bdf223 or SiI-732c2b9448cf. Though they can be used in some cases.

Sponsored by: iXsystems, Inc.
MFC after: 1 month

Add global and per-module sysctls/tunables to enable/disable metadata taste.
That should help to handle some cases when disk has some RAID metadata that
should be ignored, especially during boot.

MFC after: 3 days

Remove some hardcoded constants from code.

Plug small memory leaks.

Add support for RAID5R. Slightly improve support for RAIDMDF.

Fix bug causing memory corruption and panics with big-endian metadata.

Add optional -o argument to the `graid label ` to specify some metadata
format options. Use it for specifying byte order for the DDF metadata:
big-endian defined by specification and little-endian used by Adaptec.

Improve spare disks support. Unluckily, for some reason Adaptec 1430SA
RAID BIOS doesn't want to understand spare disks created by graid. But
at least spares created by BIOS are working fine now.

Implement volume deletion if disk has more then one partition.

Improve DDF metadata writing.

Add to GEOM RAID class module, supporting the DDF metadata format, as
defined by the SNIA Common RAID Disk Data Format Specification v2.0.

Supports multiple volumes per array and multiple partitions per disk.
Supports standard big-endian and Adaptec's little-endian byte ordering.
Supports all single-layer RAID levels. Dual-layer RAID levels except
RAID10 are not supported now because of GEOM RAID design limitations.

Some work is still to be done, but the present code already manages basic
interoperation with RAID BIOS of the Adaptec 1430SA SATA RAID controller.

MFC after: 1 month
Sponsored by: iXsystems, Inc.