vm-virtio, virtio-devices: Split device implementation from virt queues

Split the generic virtio code (queues and device type) from the
VirtioDevice trait, transport and device implementations.

This also simplifies the feature handling in vhost_user_backend as the
vm-virtio crate is no longer has any features.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vm-virtio/src/queue.rs

@@ -8,22 +8,21 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
+use crate::VirtioIommuRemapping;
 use std::cmp::min;
 use std::convert::TryInto;
 use std::fmt::{self, Display};
 use std::num::Wrapping;
 use std::sync::atomic::{fence, Ordering};
 use std::sync::Arc;
-
-use crate::device::VirtioIommuRemapping;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap,
     GuestUsize,
 };
 
-pub(super) const VIRTQ_DESC_F_NEXT: u16 = 0x1;
-pub(super) const VIRTQ_DESC_F_WRITE: u16 = 0x2;
-pub(super) const VIRTQ_DESC_F_INDIRECT: u16 = 0x4;
+pub const VIRTQ_DESC_F_NEXT: u16 = 0x1;
+pub const VIRTQ_DESC_F_WRITE: u16 = 0x2;
+pub const VIRTQ_DESC_F_INDIRECT: u16 = 0x4;
 
 #[derive(Debug)]
 pub enum Error {
@@ -718,15 +717,12 @@ impl Queue {
     }
 }
 
-#[cfg(test)]
-pub(crate) mod tests {
-    extern crate vm_memory;
-
+pub mod testing {
+    use super::*;
     use std::marker::PhantomData;
     use std::mem;
-
-    pub use super::*;
-    use vm_memory::{GuestAddress, GuestMemoryMmap, GuestUsize};
+    use vm_memory::Bytes;
+    use vm_memory::{Address, GuestAddress, GuestMemoryMmap, GuestUsize};
 
     // Represents a location in GuestMemoryMmap which holds a given type.
     pub struct SomeplaceInMemory<'a, T> {
@@ -790,7 +786,7 @@ pub(crate) mod tests {
     }
 
     impl<'a> VirtqDesc<'a> {
-        fn new(start: GuestAddress, mem: &'a GuestMemoryMmap) -> Self {
+        pub fn new(start: GuestAddress, mem: &'a GuestMemoryMmap) -> Self {
             assert_eq!(start.0 & 0xf, 0);
 
             let addr = SomeplaceInMemory::new(start, mem);
@@ -930,15 +926,15 @@ pub(crate) mod tests {
             self.dtable.len() as u16
         }
 
-        fn dtable_start(&self) -> GuestAddress {
+        pub fn dtable_start(&self) -> GuestAddress {
             self.dtable.first().unwrap().start()
         }
 
-        fn avail_start(&self) -> GuestAddress {
+        pub fn avail_start(&self) -> GuestAddress {
             self.avail.flags.location
         }
 
-        fn used_start(&self) -> GuestAddress {
+        pub fn used_start(&self) -> GuestAddress {
             self.used.flags.location
         }
 
@@ -963,6 +959,15 @@ pub(crate) mod tests {
             self.used.end()
         }
     }
+}
+
+#[cfg(test)]
+pub mod tests {
+    extern crate vm_memory;
+
+    use super::testing::*;
+    pub use super::*;
+    use vm_memory::{GuestAddress, GuestMemoryMmap};
 
     #[test]
     fn test_checked_new_descriptor_chain() {