Merge branch 'vsock-add-local-transport-support'

Stefano Garzarella says:

====================
vsock: add local transport support

v2:
 - style fixes [Dave]
 - removed RCU sync and changed 'the_vsock_loopback' in a global
   static variable [Stefan]
 - use G2H transport when local transport is not loaded and remote cid
   is VMADDR_CID_LOCAL [Stefan]
 - rebased on net-next

v1: https://patchwork.kernel.org/cover/11251735/



This series introduces a new transport (vsock_loopback) to handle
local communication.
This could be useful to test vsock core itself and to allow developers
to test their applications without launching a VM.

Before this series, vmci and virtio transports allowed this behavior,
but only in the guest.
We are moving the loopback handling in a new transport, because it
might be useful to provide this feature also in the host or when
no H2G/G2H transports (hyperv, virtio, vmci) are loaded.

The user can use the loopback with the new VMADDR_CID_LOCAL (that
replaces VMADDR_CID_RESERVED) in any condition.
Otherwise, if the G2H transport is loaded, it can also use the guest
local CID as previously supported by vmci and virtio transports.
If G2H transport is not loaded, the user can also use VMADDR_CID_HOST
for local communication.

Patch 1 is a cleanup to build virtio_transport_common without virtio
Patch 2 adds the new VMADDR_CID_LOCAL, replacing VMADDR_CID_RESERVED
Patch 3 adds a new feature flag to register a loopback transport
Patch 4 adds the new vsock_loopback transport based on the loopback
        implementation of virtio_transport
Patch 5 implements the logic to use the local transport for loopback
        communication
Patch 6 removes the loopback from virtio_transport
====================

Signed-off-by: David S. Miller <davem@davemloft.net>