Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r261147, r261149:

- Remove spaces before tabs in the function prototype list
- Read each field of the configuration individually

MFC r260582, r260583:

- Add unmapped IO support to virtio_blk(4)
- Add unmapped IO support to virtio_scsi(4)

MFC r260566: Remove incorrect bit shift when assigning the LUN request field

MFC VirtIO r252702,r252703,r252704,r252706,r252707,r252708,r252709

This brings in several bug fixes and better conformance with various
aspects of the spec that have changed.

r252702: Convert VirtIO to use ithreads instead of taskqueues
r252703: Block driver bug fixes and spec changes
r252704: Balloon driver improvements
r252706: Minor network driver improvements
r252707: Minor misc VirtIO changes
r252708: PCI driver bug fixes and cleanup
r252709: Fix SCSI driver lock not owned panic

MFC r249468:
Stop abusing xpt_periph in random plases that really have no periph related
to CCB, for example, bus scanning. NULL value is fine in such cases and it
is correctly logged in debug messages as "noperiph". If at some point we
need some real XPT periphs (alike to pmpX now), quite likely they will be
per-bus, and not a single global instance as xpt_periph now.

Big MFC of the physbio changes necessary for unmapped I/O. These changes
have been in production at Netflix for several months with significant
success.

MFC r246713:

Reform the busdma API so that new types may be added without modifying
every architecture's busdma_machdep.c. It is done by unifying the
bus_dmamap_load_buffer() routines so that they may be called from MI
code. The MD busdma is then given a chance to do any final processing
in the complete() callback.

MFC r249538:
Some compilers issue a warning when wider integer is casted to narrow
pointer. Supposedly shut down the warning by casting through
uintptr_t.

MFC r251479:
Simplify the checking of flags for cam_periph_mapmem(). This gets rid of
a lot of code redundancy and grossness at very minor expense.

MFC r251837:
MFC r251842:
Add infrastructure for doing compatibility shims, as has been sorely
needed for the last 10 years. Far too much of the internal API is
exposed, and every small adjustment causes applications to stop working.
To kick this off, bump the API version to 0x17 as should have been done
with r246713, but add shims to compensate. Thanks to the shims, there
should be no visible change in application behavior.

Submitted by: kib, jeffr
Approved by: kib
Obtained from: Netflix

MFC r238072,r238360,r240430,r241469,r241470,r241495,r244136,r244200

Sync VirtIO with HEAD.

- r238072: Do not include <sys/types.h> in the local headers.
- r238360: Various VirtIO improvements
- r240430: No need to leak these into the includer's namespace.
- r241469: virtqueue: Fix non-indirect virtqueues
- r241470: Add Virtio SCSI driver
- r241495: Fix build with PAE enabled
- r244136: Remove duplicated lines
- r244200: Start taskqueues threads after attach cannot fail

Approved by: grehan (mentor)

Virtio SCSI driver

Submitted by: Bryan Venteicher bryanv at daemoninthecloset dot org
Reviewed by: grehan