The enum forwards any calls made from the functions
defined in the VsockConnectionBackend trait to the
backing connection. the types are stream and seqpacket
based connections.

Signed-off-by: aerosouund <aerosound161@gmail.com>

Can be a seqpacket or stream. Refactor vsock.rs methods
to expect it in function calls and use it in building structs.
add a VSOCK_TYPE_SEQPACKET constant to denote seqpacket
connections

Signed-off-by: aerosouund <aerosound161@gmail.com>

- Make the multiplexer use a VsockConnection<ConnBackend> for its
  conn_map values to forward calls to stream or seqpacket types.
- Make the host sock a boxed implementation of the Socket trait which
  exposes the accept() method with different implementations for stream
  and seqpacket connections.
- Globally replace the MuxerConnection type with a VsockConnection
  generic over a ConnBackend.
- Make the init_pkt_hdr method add different type constants based on
  the vsock type.
- pass vsock type to read_local_stream_port. seqpacket sockets
  necessitate that you read the message in one go.

Signed-off-by: aerosouund <aerosound161@gmail.com>

Add a new field to the vsock api and modify functions that interact with
a VsockDeviceConfig or a VsockUnixBackend.

Signed-off-by: aerosouund <aerosound161@gmail.com>

- incoming length is a trait with a default implementation to read the
  size of an incoming message from a connection fd
- read result stores the count of bytes read and whether or no another
  receive should be triggered
- change the VsockChannel trait to return a ReadResult instead of null

Signed-off-by: aerosouund <aerosound161@gmail.com>

- create a set_msg_eom function to set eom in the packet header
- create a set_msg_eor function to set eor in the packet header

Signed-off-by: aerosouund <aerosound161@gmail.com>

- make it start another loop iteration if it received a result with
  should_retrigger

Signed-off-by: aerosouund <aerosound161@gmail.com>

- add connection_buffer and conn_buffer_wrote_bytes fields to the
  connection
- when there's a seqpacket connection with incoming data check the
  length of the incoming message
- if its small enough to fit in the packet buffer (1 memory page size)
  receive directly from the af_unix to the buffer
- if its bigger, receive into a buffer then copy whatever you can fit
  into the buffer and mark that we should retrigger
- if the buffer has data, don't read from the stream. iterate until you
  finish the buffer
- don't use intermediate rx buffering for stream connections
- if the incoming message is larger than the connection buffer
  we return VsockError::MessageTooLong

Signed-off-by: aerosouund <aerosound161@gmail.com>

- propagate conn_buffer_size to connections on creation to determine
  how big the rx intermediate buffer should be
- if the result coming from the connection has should_retrigger push to
  the rx queue to mark that there's still data to be read from the
buffer

Signed-off-by: aerosouund <aerosound161@gmail.com>

- the setting should be persisted across snapshot and restore so the new
  vsock buffers have the same size
- prevent the caller from passing too large buffers. 256 is also the
  limit set by the linux kernel
- prevent the caller from passing too small buffers (less than 4096)
  bytes.
- make the field default to none and add default serialization

Signed-off-by: aerosouund <aerosound161@gmail.com>

- seqpacket sockets necessitate a different flag set than
  whats currently in the seccomp rules. we need to add
  seqpacket with SOCK_CLOEXEC for testing to work

Signed-off-by: aerosouund <aerosound161@gmail.com>

- the functional tests use an echo server which is just a socat command.
  socat doesn't support seqpacket.
- the program listens on a port and handles a connection in a separate
  thread

Signed-off-by: aerosouund <aerosound161@gmail.com>

- can be stream or seqpacket. to facilitate seqpacket testing

Signed-off-by: aerosouund <aerosound161@gmail.com>

- create a fixture to compile the vsock_seq_server program
- create start_seqpacket_echo_server to run the program in
  the vm
- create the check_guest_connections_seqpacket function to
  start a host side seqpacket server and connect to it from
  the guestn and check data hash
- create h2g, g2h and overflow functional tests
- run seqpacket tests on kernel 6.x only because seqpacket
  was introduced in linux 5.14. any previous version would
  fail

Signed-off-by: aerosouund <aerosound161@gmail.com>

- so that the api anticipates it

Signed-off-by: aerosouund <aerosound161@gmail.com>

add changelog entry for the modified field

Signed-off-by: aerosouund <aerosound161@gmail.com>

- Added to the unreleased section

Signed-off-by: aerosouund <aerosound161@gmail.com>