Crate vhost

Virtio Vhost Backend Drivers

Virtio devices use virtqueues to transport data efficiently. The first generation of virtqueue is a set of three different single-producer, single-consumer ring structures designed to store generic scatter-gather I/O. The virtio specification 1.1 introduces an alternative compact virtqueue layout named “Packed Virtqueue”, which is more friendly to memory cache system and hardware implemented virtio devices. The packed virtqueue uses read-write memory, that means the memory will be both read and written by both host and guest. The new Packed Virtqueue is preferred for performance.

Vhost is a mechanism to improve performance of Virtio devices by delegate data plane operations to dedicated IO service processes. Only the configuration, I/O submission notification, and I/O completion interruption are piped through the hypervisor. It uses the same virtqueue layout as Virtio to allow Vhost devices to be mapped directly to Virtio devices. This allows a Vhost device to be accessed directly by a guest OS inside a hypervisor process with an existing Virtio (PCI) driver.

The initial vhost implementation is a part of the Linux kernel and uses ioctl interface to communicate with userspace applications. Dedicated kernel worker threads are created to handle IO requests from the guest.

Later Vhost-user protocol is introduced to complement the ioctl interface used to control the vhost implementation in the Linux kernel. It implements the control plane needed to establish virtqueues sharing with a user space process on the same host. It uses communication over a Unix domain socket to share file descriptors in the ancillary data of the message. The protocol defines 2 sides of the communication, master and slave. Master is the application that shares its virtqueues. Slave is the consumer of the virtqueues. Master and slave can be either a client (i.e. connecting) or server (listening) in the socket communication.

Modules

• net
  Trait to control vhost-net backend drivers.
• vdpa
  Trait to control vhost-vdpa backend drivers.
• vhost_kern
  Traits and structs to control Linux in-kernel vhost drivers.
• vhost_user
  The protocol for vhost-user is based on the existing implementation of vhost for the Linux Kernel. The protocol defines two sides of the communication, master and slave. Master is the application that shares its virtqueues. Slave is the consumer of the virtqueues.
• vsock
  Trait to control vhost-vsock backend drivers.

Structs

• VhostIotlbMsg
  Vhost IOTLB message structure.
• VhostUserDirtyLogRegion
  Shared memory region data for logging dirty pages
• VhostUserMemoryRegionInfo
  Memory region configuration data.
• VringConfigData
  Vring configuration data.

Enums

• Error
  Error codes for vhost operations
• VhostAccess
  Vhost memory access permission (VHOST_ACCESS_* mapping)
• VhostIotlbType
  Vhost IOTLB message type (VHOST_IOTLB_* mapping)

Constants

• VHOST_MAX_MEMORY_REGIONS
  Maximum number of memory regions supported.

Traits

• VhostBackend
  An interface for setting up vhost-based backend drivers with interior mutability.
• VhostBackendMut
  An interface for setting up vhost-based backend drivers.
• VhostIotlbBackend
  An interface for IOTLB messages support for vhost-based backend
• VhostIotlbMsgParser
  Vhost IOTLB message parser.

Type Definitions

• Result
  Result of vhost operations