qemu-system-arm sharing host disk using virtiofsd

[Dave Turvene - Work]

Greetings -

I'm not sure this is the best group to ask the following question but
I'll start here.

I use qemu to develop openwrt code.  I currently use a 9p mount to share
my code/cross-compile directory to the arm guest in order to run/test
the code.  openwrt uses the musl library so this works pretty well.

I use Ubuntu 18.04 for host, qemu 5.1, openwrt 19.07 for guest. I
configure/make both the qemu executable and openwrt kernel/rootfs.

My research indicates virtiofsd is now the preferred way to share host
dirs to the guest and I see points in the qemu 5.1 code that reference
virtiofsd.

* https://qemu.readthedocs.io/en/latest/tools/virtiofsd.html

* There is a $Q_TOP/tools/virtiofsd directory which is empty.  

*  `find . -name "Makefile*" | xargs grep virtiofsd` shows a lot of hits.

I cannot figure out how to create virtiofsd using my QEMU 5.1 source
tree.  And the instructions at
`https://virtio-fs.gitlab.io/howto-qemu.html` fail spectatularly.

I must be missing something obvious; please point me in the right
direction.  9P still works fine so I'm not interested in spending a lot
of time on this.

Dave Turvene