virtio-queue: Introduce new crate forked from rust-vmm/vm-virtio

This crate contains a new definition of the Queue, AvailIter,
DescriptorChain and Descriptor structures forked from the upstream
crate rust-vmm/vm-virtio d62f2246568d4f544e848b23c025b268effac5ca.

The following patches have been applied on top of this base in order to
make it work correctly with Cloud Hypervisor requirements:

- Add MSI vector field to the Queue

  In order to help with MSI/MSI-X support, it is convenient to store the
  value of the interrupt vector inside the Queue directly.

- Handle address translations

  For devices with access to data in memory being translated, we add to
  the Queue the ability to translate the address stored in the
  descriptor.
  It is very helpful as it performs the translation right after the
  untranslated address is read from memory, avoiding any errors from
  happening from the consumer's crate perspective. It also allows the
  consumer to reduce greatly the amount of duplicated code for applying
  the translation in many different places.

- Add helpers for Queue structure

  They are meant to help crate's consumers getting/setting information
  about the Queue.

These patches can be found on the 'ch' branch from the Cloud Hypervisor
fork: https://github.com/cloud-hypervisor/vm-virtio.git

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

virtio-queue/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "virtio-queue"
+version = "0.1.0"
+authors = ["The Chromium OS Authors"]
+description = "virtio queue implementation"
+repository = "https://github.com/rust-vmm/vm-virtio"
+keywords = ["virtio"]
+readme = "README.md"
+license = "Apache-2.0 OR MIT"
+edition = "2018"
+
+[features]
+test-utils = []
+
+[dependencies]
+vm-memory = "0.6.0"
+vmm-sys-util = ">=0.8.0"
+log = ">=0.4.6"

virtio-queue/src/defs.rs

@@ -0,0 +1,46 @@
+// Copyright 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0 OR BSD-3-Clause
+
+//! Virtio queue related constant definitions
+
+/// Marks a buffer as continuing via the next field.
+pub const VIRTQ_DESC_F_NEXT: u16 = 0x1;
+
+/// Marks a buffer as device write-only.
+pub const VIRTQ_DESC_F_WRITE: u16 = 0x2;
+
+/// Shows that the buffer contains a list of buffer descriptors.
+pub const VIRTQ_DESC_F_INDIRECT: u16 = 0x4;
+
+/// Used flags
+pub const VIRTQ_USED_F_NO_NOTIFY: u16 = 0x1;
+
+/// This is the size of one element in the used ring, id (le32) + len (le32).
+pub(crate) const VIRTQ_USED_ELEMENT_SIZE: u64 = 8;
+
+/// Used ring header: flags (u16) + idx (u16)
+pub(crate) const VIRTQ_USED_RING_HEADER_SIZE: u64 = 4;
+
+/// This is the size of the used ring metadata: header + avail_event (le16).
+/// The total size of the used ring is:
+/// VIRTQ_USED_RING_HMETA_SIZE + VIRTQ_USED_ELEMENT_SIZE * queue_size
+pub(crate) const VIRTQ_USED_RING_META_SIZE: u64 = VIRTQ_USED_RING_HEADER_SIZE + 2;
+
+/// This is the size of one element in the available ring (le16).
+pub(crate) const VIRTQ_AVAIL_ELEMENT_SIZE: u64 = 2;
+
+/// Avail ring header: flags(u16) + idx(u16)
+pub(crate) const VIRTQ_AVAIL_RING_HEADER_SIZE: u64 = 4;
+
+/// This is the size of the available ring metadata: header + used_event (le16).
+/// The total size of the available ring is:
+/// VIRTQ_AVAIL_RING_META_SIZE + VIRTQ_AVAIL_ELEMENT_SIZE * queue_size
+pub(crate) const VIRTQ_AVAIL_RING_META_SIZE: u64 = VIRTQ_AVAIL_RING_HEADER_SIZE + 2;
+
+/// The Virtio Spec 1.0 defines the alignment of VirtIO descriptor is 16 bytes,
+/// which fulfills the explicit constraint of GuestMemory::read_obj().
+pub(crate) const VIRTQ_DESCRIPTOR_SIZE: usize = 16;
+
+/// Vector value used to disable MSI for a queue.
+pub const VIRTQ_MSI_NO_VECTOR: u16 = 0xffff;