Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

MFC r267520, r267521, r267522, r267523, r267524:

- Remove two write-only local variables
- Remove unused element in the vtnet_rxq structure
- Remove kernel specific macro out of the VirtIO PCI header file
- Move the VIRTIO_RING_F_* defines out of virtqueue.h into
virtio_config.h
- Make the feature negotiation code easier to follow
- Force two byte alignment for all control message headers

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

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

Various VirtIO improvements

PCI:
- Properly handle interrupt fallback from MSIX to MSI to legacy.
The host may not have sufficient resources to support MSIX,
so we must be able to fallback to legacy interrupts.
- Add interface to get the (sub) vendor and device IDs.
- Rename flags to VTPCI_FLAG_* like other VirtIO drivers.
Block:
- No longer allocate vtblk_requests from separate UMA zone.
malloc(9) from M_DEVBUF is sufficient. Assert segment counts
at allocation.
- More verbose error and debug messages.
Network:
- Remove stray write once variable.
Virtqueue:
- Shuffle code around in preparation of converting the mb()s to
the appropriate atomic(9) operations.
- Only walk the descriptor chain when freeing if INVARIANTS is
defined since the result is only KASSERT()ed.

Submitted by: Bryan Venteicher (bryanv@daemoninthecloset.org)

Catch up with Bryan Venteicher's virtio Hg repo:

c162516
Remove vtblk_sector_size

c162515
Wrap long license lines

c162514
Remove vtblk_unit

c162513
Wrap long lines in the license.

c162512
Remove verbose messages when link goes up/down.

A similar message is printed elsewhere as a result of
if_link_state_change().

c162511
Explicity compare pointer to NULL

c162510
Allocate the mac filter table at attach time.

c162509
Add real BSD licenses to the header files copied from Linux.

The chases upstream changes made in Linux awhile ago.

c162508
Only notify if we actually dequeued something.

c162507
Change a couple of if () { KASSERT(...) } to just KASSERTs.

In non-debug kernels, the if() { } probably get optomized
away, but I guess this is clearer.

c162506
Remove VIRTIO_BLK_F_TOPOLOGY fields in the config.

TOPOLOGY has since been removed from the spec, and the FreeBSD
didn't really do anything with the fields anyways.

c162505
Move vtblk_enqueue_request() outside the locks when getting the ident.

c162504
Remove soon to be uneeded trylock during dump [1].
http://lists.freebsd.org/pipermail/freebsd-current/2011-November/029226.html

c162503
Remove emtpy line

c162502
Drop frame if cannot allocate a vtnet_tx_header.

If we don't, we set OACTIVE, but if there are no
other frames in flight, vtnet_txeof() will never
be called to unset OACTIVE. The interface would
have to be down/up'ed in order to become usable.

We could be cuter here and only do this if the
virtqueue is emtpy, but its probably not worth
the complication.

c162501
Start mbuf replacement loop at 1 for clarity

Obtained from: Bryan Venteicher bryanv at daemoninthecloset dot org

Import virtio base, PCI front-end, and net/block/balloon drivers.
Tested on Qemu/KVM, VirtualBox, and BHyVe.

Currently built as modules-only on i386/amd64. Man pages not yet hooked
up, pending review.

Submitted by: Bryan Venteicher bryanv at daemoninthecloset dot org
Reviewed by: bz
MFC after: 4 weeks or so