Merge branch 'vsock-add-flags-field-in-the-vsock-address'

Merge branch 'vsock-add-flags-field-in-the-vsock-address'

Andra Paraschiv says:

====================
vsock: Add flags field in the vsock address

vsock enables communication between virtual machines and the host they are
running on. Nested VMs can be setup to use vsock channels, as the multi
transport support has been available in the mainline since the v5.5 Linux
kernel has been released.

Implicitly, if no host->guest vsock transport is loaded, all the vsock packets
are forwarded to the host. This behavior can be used to setup communication
channels between sibling VMs that are running on the same host. One example can
be the vsock channels that can be established within AWS Nitro Enclaves
(see Documentation/virt/ne_overview.rst).

To be able to explicitly mark a connection as being used for a certain use case,
add a flags field in the vsock address data structure. The value of the flags
field is taken into consideration when the vsock transport is assigned. This
way can distinguish between different use cases, such as nested VMs / local
communication and sibling VMs.

The flags field can be set in the user space application connect logic. On the
listen path, the field can be set in the kernel space logic.
====================

Link: https://lore.kernel.org/r/20201214161122.37717-1-andraprs@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>