vhost_user_backend: Add new crate

The purpose of this new crate is to provide a common library to all
vhost-user backend implementations. The more is handled by this library,
the less duplication will need to happen in each vhost-user daemon.

This crate relies a lot on vhost_rs, vm-memory and vm-virtio crates.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vhost_user_backend/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "vhost_user_backend"
+version = "0.1.0"
+authors = ["The Cloud Hypervisor Authors"]
+edition = "2018"
+
+[features]
+default = []
+pci_support = ["vm-virtio/pci_support"]
+mmio_support = ["vm-virtio/mmio_support"]
+
+[dependencies]
+epoll = "4.1.0"
+libc = "0.2.60"
+vm-memory = { git = "https://github.com/rust-vmm/vm-memory" } 
+vm-virtio = { path = "../vm-virtio" }
+vmm-sys-util = { git = "https://github.com/rust-vmm/vmm-sys-util" }
+
+[dependencies.vhost_rs]
+path = "../vhost_rs"
+features = ["vhost-user-slave"]
+
+[workspace]