bhyve: change vq_getchain to return iovecs in both directions

[khng]

Summary

bhyve: change vq_getchain to return read and write iovecs

The old prototype requires callers to inspect flags of each descriptors
to get the starting position of host-to-guest iovecs.

vq_getchain() is changed to return a virtio request with both the
guest-to-host iovecs and host-to-guest iovecs recorded instead.
Callers can obtain the host-to-guest iovecs directly.

Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks

[khng]

• Fixed loopy check fallout out when num of descs are equal to maximum number
• No need to use memset in vq_getchain

[afedorov]

usr.sbin/bhyve/pci_virtio_9p.c

200–201

It looks like the flags[] array is no longer used.

215

Debug output doesn't make sense anymore.

[khng]

• Remove unused flags from pci_vt9p_notify

[afedorov]

usr.sbin/bhyve/pci_virtio_scsi.c

623

enqueuedvi -> enqueued

[khng]

Refactor the prototype to match vq_ring_enqueue_segments in sys/dev/virtio/virtqueue.c.

[khng]

@afedorov I would like to have some comments on this again.

[philip]

usr.sbin/bhyve/pci_virtio_block.c

348

The previous comment inside the loop (deleted lines 348-354 in this diff) was a little clearer. I agree that the assertion should be outside the loop but the comment could be a little clearer. To a casual reader, the assertion is inverted.

usr.sbin/bhyve/virtio.c

277

It would look very slightly neater to initialise this further down, rather than where it's declared. None of the other stack variables are initialised at the top of this function.

285

E.g. initialise req = { 0 }; here.

[khng]

Style.

[philip]

Great! Thank you.

Approved by: philip (mentor)

[afedorov]

usr.sbin/bhyve/virtio.c

216–218

“vs” argument is unused.