VirtFS support in bhyve

[jceel at FreeBSD.org]

Hello,

I'm working on virtio-9p (so-called VirtFS) support in bhyve. Project consists of two parts: BSD-licensed lib9p library and actual virtio-9p driver. Right now it's able to do filesystem passthrough using 9P2000.u protocol to Linux guests.

You can check it out here: https://github.com/jceel/freebsd/tree/virtfs

Syntax:
bhyve side: append `-s <n>,virtio-9p,sharename=/host/path`
linux side: `mount -t 9p -o trans=virtio -o version=9p2000.u sharename /mnt/guest/path`

Using 9p as root filesystem for Linux guests should work too.

Plans:
- Definitely in-kernel 9pfs filesystem support for FreeBSD guests using same lib9p library
- 9P2000.L support (adds ACLs, extattrs, file locks, atomic reads/writes and so on)
- Filesystem backend using AIO
- Ability to export multiple trees for different "aname" values using one virtio-9p device (that's actually a low-hanging fruit)

I'm looking forward to your feedback - keep in mind that's totally experimental/incomplete/nonworking code.

Jakub.