vmm: dbus: implement the D-Bus API

This commit introduces three new dependencies: `zbus`, `futures`
and `blocking`. `blocking` is used to call the Internal API in zbus'
async context which is driven by `futures::executor`. They are all
behind the `dbus_api` feature flag.

The D-Bus API implementation is behind the same `dbus_api` feature
flag as well.

Signed-off-by: Omer Faruk Bayram <omer.faruk@sartura.hr>

vmm/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 
 [features]
 default = []
+dbus_api = ["blocking", "futures", "zbus"]
 guest_debug = ["kvm", "gdbstub", "gdbstub_arch"]
 kvm = ["hypervisor/kvm", "vfio-ioctls/kvm", "vm-device/kvm", "pci/kvm"]
 mshv = ["hypervisor/mshv", "vfio-ioctls/mshv", "vm-device/mshv", "pci/mshv"]
@@ -19,9 +20,11 @@ arc-swap = "1.5.1"
 arch = { path = "../arch" }
 bitflags = "1.3.2"
 block_util = { path = "../block_util" }
+blocking = { version = "1.3.0", optional = true }
 devices = { path = "../devices" }
 epoll = "4.3.1"
 event_monitor = { path = "../event_monitor" }
+futures = { version = "0.3.27", optional = true }
 gdbstub = { version = "0.6.4", optional = true }
 gdbstub_arch = { version = "0.2.4", optional = true }
 hypervisor = { path = "../hypervisor" }
@@ -55,4 +58,5 @@ vm-memory = { version = "0.10.0", features = ["backend-mmap", "backend-atomic",
 vm-migration = { path = "../vm-migration" }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = { version = "0.11.0", features = ["with-serde"] }
-zerocopy = "0.6.1"
+zbus = { version = "3.11.1", optional = true }
+zerocopy = "0.6.1"