vmm: Add ability to add virtio-fs device post-boot

Adds DeviceManager method `make_virtio_fs_device` which creates a single
device, and modifies `make_virtio_fs_devices` to use this method.

Implements the new `vm.add-fs route`.

Signed-off-by: Dean Sheather <dean@coder.com>

vmm/src/api/mod.rs

@@ -37,7 +37,9 @@ pub use self::http::start_http_thread;
 pub mod http;
 pub mod http_endpoint;
 
-use crate::config::{DeviceConfig, DiskConfig, NetConfig, PmemConfig, RestoreConfig, VmConfig};
+use crate::config::{
+    DeviceConfig, DiskConfig, FsConfig, NetConfig, PmemConfig, RestoreConfig, VmConfig,
+};
 use crate::vm::{Error as VmError, VmState};
 use std::io;
 use std::sync::mpsc::{channel, RecvError, SendError, Sender};
@@ -122,6 +124,9 @@ pub enum ApiError {
     /// The disk could not be added to the VM.
     VmAddDisk(VmError),
 
+    /// The fs could not be added to the VM.
+    VmAddFs(VmError),
+
     /// The pmem device could not be added to the VM.
     VmAddPmem(VmError),
 
@@ -230,6 +235,9 @@ pub enum ApiRequest {
     /// Add a disk to the VM.
     VmAddDisk(Arc<DiskConfig>, Sender<ApiResponse>),
 
+    /// Add a fs to the VM.
+    VmAddFs(Arc<FsConfig>, Sender<ApiResponse>),
+
     /// Add a pmem device to the VM.
     VmAddPmem(Arc<PmemConfig>, Sender<ApiResponse>),
 
@@ -484,6 +492,24 @@ pub fn vm_add_disk(
     Ok(())
 }
 
+pub fn vm_add_fs(
+    api_evt: EventFd,
+    api_sender: Sender<ApiRequest>,
+    data: Arc<FsConfig>,
+) -> ApiResult<()> {
+    let (response_sender, response_receiver) = channel();
+
+    // Send the VM add-fs request.
+    api_sender
+        .send(ApiRequest::VmAddFs(data, response_sender))
+        .map_err(ApiError::RequestSend)?;
+    api_evt.write(1).map_err(ApiError::EventFdWrite)?;
+
+    response_receiver.recv().map_err(ApiError::ResponseRecv)??;
+
+    Ok(())
+}
+
 pub fn vm_add_pmem(
     api_evt: EventFd,
     api_sender: Sender<ApiRequest>,