[Virtio-fs] Issues with the virtio-fs Windows how-to (unexpected read-only file system)

[Jonathan Watt]

Hello list,

Thank you all for your work on virtio-fs. It's a very exciting step forward!

Like others[1], I've encountered the issue where virtio-fs mounted file systems
are unexpectedly read-only/inaccessible on Windows.

I worked through the Windows how-to page[2], but the "Installing the virtio-fs
service" instructions at the bottom did not work for me, as written. The
instructions are to set the new `VirtioFsSvc` service to depend on both
`WinFsp.Launcher` and `VirtioFsDrv`. However, like others, I found that the new
service would not run since `VirtioFsDrv` does not appear to exist (be a service).

After opening `regedit`, opening the key:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VirtioFsSvc

removing `VirtioFsDrv` from the value of `DependsOnService`, and then restarting
the `VirtioFsSvc` service, the file system shared via virtio-fs appeared at
'Z:\' and worked as expected. However, this only works until the Windows VM is
rebooted.

On rebooting the Windows VM, the shared file system becomes read-only and its
sub-directories cannot be opened. Manually restarting the `VirtioFsSvc` service
gets the share working again (until next reboot). This seems to indicate that
`VirtioFsSvc` is running too early, and that it really does need to wait for
*something* else to be ready before starting.

I suppose the first question is what is `VirtioFsDrv` and where is it supposed
to come from? Are there steps missing from the Windows how-to or has the name of
this service changed?

-Jonathan

1. For example, the comments starting here:
https://github.com/virtio-win/kvm-guest-drivers-windows/issues/473#issuecomment-658379853

2. https://virtio-fs.gitlab.io/howto-windows.html