ocaml-hvsock -- bindings for Hyper-V AF_VSOCK

These bindings allow Host <-> VM communication on Hyper-V systems on both Linux
and Windows.

Warning: the AF_HYPERV patches for Linux are not yet merged and hence the
definition of AF_HYPERV is not yet stable. If other address families are merged
before this one then the value of AF_HYPERV will change!

Please read the API documentation.

Example

An address on a Hyper-V host consists of two parts:

• a VM GUID

• a well-known service GUID

First generate yourself a service GUID and add this to the registry: this is like
opening a hole in a firewall for a TCP port.

New-Item -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization\GuestCommunicationServices" -Name <Service GUID>

Second discover the GUID of the VM you wish to talk to:

(Get-VM -Name <MY VM NAME>).Id

Third, run a listening server in the VM:

./hvcat -l --echo <Service GUID>

Finally, connect the client on the host to the VM:

./hvcat --vmid <VM GUID> <Service GUID>

Limitations

Although the connections use the regular SOCKET APIs, current kernels don't support
calls like select so we must always use blocking I/O from background threads, rather
than regular asynchronous I/O. This means that the Lwt connection type has been made
opaque.

The client connect call seems to block forever if the server calls listen
after the client calls connect. The Lwt_hvsock.connect works around this
with a self-imposed 1s timeout after which time it will raise ECONNREFUSED.

Background

For background, see the MSDN article on making an integration service