vm-virtio: Add update_memory() to VirtioDevice trait

The virtio devices backed by a vhost-user backend must send an update to
the associated backend with the new file descriptors corresponding to
the memory regions.

This patch allows such devices to be notified when such update needs to
happen.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-virtio/src/device.rs

@@ -6,7 +6,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
-use super::*;
+use crate::{ActivateResult, Error, Queue};
 use std::sync::Arc;
 use vm_memory::{GuestAddress, GuestMemoryAtomic, GuestMemoryMmap, GuestUsize};
 use vmm_sys_util::eventfd::EventFd;
@@ -106,6 +106,10 @@ pub trait VirtioDevice: Send {
     /// every device as part of shutting down the VM. Acting on the device
     /// after a shutdown() can lead to unpredictable results.
     fn shutdown(&mut self) {}
+
+    fn update_memory(&mut self, _mem: &GuestMemoryMmap) -> std::result::Result<(), Error> {
+        Ok(())
+    }
 }
 
 /// Trait providing address translation the same way a physical DMA remapping

vm-virtio/src/lib.rs

@@ -175,4 +175,5 @@ pub enum Error {
     EpollCtl(io::Error),
     EpollWait(io::Error),
     FailedSignalingDriver(io::Error),
+    VhostUserUpdateMemory(vhost_user::Error),
 }