Vhost Serial

The vhost serial driver is the device side of virtio-console. It forwards the data between the peer’s virtio-console driver and a local character device: data the peer queues on the TX virtqueue is written to the local device, and data read from the local device is returned on the RX virtqueue. It handles both VIRTIO_ID_CONSOLE and VIRTIO_ID_RPROC_SERIAL.

Configuration

• CONFIG_DRIVERS_VHOST_SERIAL: enable the driver. It selects CONFIG_DRIVERS_VHOST.

• CONFIG_DRIVERS_VHOST_SERIAL_PRIORITY: priority of the RX and TX kernel threads (default 224).

• CONFIG_DRIVERS_VHOST_SERIAL_STACKSIZE: stack size of the RX and TX kernel threads (default CONFIG_DEFAULT_TASK_STACKSIZE).

Device config space

The device config space holds struct vhost_serial_config_s from include/nuttx/virtio/virtio-serial.h:

begin_packed_struct struct vhost_serial_config_s
{
  struct virtio_serial_config_s config;
  char path[VIRTIO_SERIAL_PATH_SIZE];
} end_packed_struct;

path names the local character device the driver opens at probe time, for example "/dev/ttyS1". The resource table author fills it in; the driver treats the last byte as the string terminator, so a path must be shorter than VIRTIO_SERIAL_PATH_SIZE (64) bytes. Probe fails if the device cannot be opened.