Struct vmm_vhost::backend_server::BackendServer

pub struct BackendServer<S: Backend> {
    connection: Connection<FrontendReq>,
    backend: S,
    virtio_features: u64,
    acked_virtio_features: u64,
    protocol_features: VhostUserProtocolFeatures,
    acked_protocol_features: u64,
    reply_ack_enabled: bool,
}

Handles requests from a vhost-user connection by dispatching them to [Backend] methods.

Fields

connection: Connection<FrontendReq>

Underlying connection for communication.

backend: S

virtio_features: u64

acked_virtio_features: u64

protocol_features: VhostUserProtocolFeatures

acked_protocol_features: u64

reply_ack_enabled: bool

Sending ack for messages without payload.

Implementations

impl<S: Backend> BackendServer<S>

pub fn new(connection: Connection<FrontendReq>, backend: S) -> Self

pub fn recv_header( &mut self ) -> Result<(VhostUserMsgHeader<FrontendReq>, Vec<File>)>

Receives and validates a vhost-user message header and optional files.

Since the length of vhost-user messages are different among message types, regular vhost-user messages are sent via an underlying communication channel in stream mode. (e.g. SOCK_STREAM in UNIX) So, the logic of receiving and handling a message consists of the following steps:

1. Receives a message header and optional attached file.
2. Validates the message header.
3. Check if optional payloads is expected.
4. Wait for the optional payloads.
5. Receives optional payloads.
6. Processes the message.

This method BackendServer::recv_header() is in charge of the step (1) and (2), BackendServer::needs_wait_for_payload() is (3), and BackendServer::process_message() is (5) and (6). We need to have the three method separately for multi-platform supports; BackendServer::recv_header() and BackendServer::process_message() need to be separated because the way of waiting for incoming messages differs between Unix and Windows so it’s the caller’s responsibility to wait before BackendServer::process_message().

Note that some vhost-user protocol variant such as VVU doesn’t assume stream mode. In this case, a message header and its body are sent together so the step (4) is skipped. We handle this case in BackendServer::needs_wait_for_payload().

The following pseudo code describes how a caller should process incoming vhost-user messages:

loop {
  // block until a message header comes.
  // The actual code differs, depending on platforms.
  connection.wait_readable().unwrap();

  // (1) and (2)
  let (hdr, files) = backend_server.recv_header();

  // (3)
  if backend_server.needs_wait_for_payload(&hdr) {
    // (4) block until a payload comes if needed.
    connection.wait_readable().unwrap();
  }

  // (5) and (6)
  backend_server.process_message(&hdr, &files).unwrap();
}

pub fn needs_wait_for_payload( &self, hdr: &VhostUserMsgHeader<FrontendReq> ) -> bool

Returns whether the caller needs to wait for the incoming message before calling BackendServer::process_message.

See BackendServer::recv_header’s doc comment for the usage.

pub fn process_message( &mut self, hdr: VhostUserMsgHeader<FrontendReq>, files: Vec<File> ) -> Result<()>

Main entrance to request from the communication channel.

Receive and handle one incoming request message from the frontend. See BackendServer::recv_header’s doc comment for the usage.

Return:

• Ok(()): one request was successfully handled.
• Err(ClientExit): the frontend closed the connection properly. This isn’t an actual failure.
• Err(Disconnect): the connection was closed unexpectedly.
• Err(InvalidMessage): the vmm sent a illegal message.
• other errors: failed to handle a request.

fn new_reply_header<T: Sized>( &self, req: &VhostUserMsgHeader<FrontendReq>, payload_size: usize ) -> Result<VhostUserMsgHeader<FrontendReq>>

fn send_ack_message( &mut self, req: &VhostUserMsgHeader<FrontendReq>, success: bool ) -> Result<()>

Sends reply back to Vhost frontend in response to a message.

fn send_reply_message<T: Sized + AsBytes>( &mut self, req: &VhostUserMsgHeader<FrontendReq>, msg: &T ) -> Result<()>

fn send_reply_with_payload<T: Sized + AsBytes>( &mut self, req: &VhostUserMsgHeader<FrontendReq>, msg: &T, payload: &[u8] ) -> Result<()>

fn set_mem_table( &mut self, hdr: &VhostUserMsgHeader<FrontendReq>, size: usize, buf: &[u8], files: Vec<File> ) -> Result<()>

fn get_config( &mut self, hdr: &VhostUserMsgHeader<FrontendReq>, buf: &[u8] ) -> Result<()>

fn set_config(&mut self, buf: &[u8]) -> Result<()>

fn set_backend_req_fd(&mut self, files: Vec<File>) -> Result<()>

fn handle_vring_fd_request( &mut self, buf: &[u8], files: Vec<File> ) -> Result<(u8, Option<File>)>

Parses an incoming |SET_VRING_KICK| or |SET_VRING_CALL| message into a Vring number and an fd.

fn check_request_size( &self, hdr: &VhostUserMsgHeader<FrontendReq>, size: usize, expected: usize ) -> Result<()>

fn check_attached_files( &self, hdr: &VhostUserMsgHeader<FrontendReq>, files: &[File] ) -> Result<()>

fn extract_request_body<T: Sized + FromBytes + VhostUserMsgValidator>( &self, hdr: &VhostUserMsgHeader<FrontendReq>, size: usize, buf: &[u8] ) -> Result<T>

fn update_reply_ack_flag(&mut self)

Trait Implementations

impl<S: Backend> AsRawDescriptor for BackendServer<S>

fn as_raw_descriptor(&self) -> RawDescriptor

Returns the underlying raw descriptor.

impl<S: Backend> AsRef<S> for BackendServer<S>

fn as_ref(&self) -> &S

Converts this type into a shared reference of the (usually inferred) input type.