refactor(vhost-user-block): delegate to the generic vhost-user frontend

CHANGELOG.md

@@ -82,6 +82,11 @@ and this project adheres to
   Terminating a connection now also discards its TX buffer, so the device stops
   advertising `EPOLLOUT` for a host stream it will never write to again, which
   could otherwise busy-spin the event thread indefinitely.
+- [#6083](https://github.com/firecracker-microvm/firecracker/pull/6083): Fixed a
+  vhost-user-block device backed by a readonly backend not being treated as
+  readonly. The `VIRTIO_BLK_F_RO` check read the acked feature set after it had
+  been narrowed to the vhost-user protocol bit, so it never matched, and a
+  readonly vhost-user root device was given `rw` on the guest kernel cmdline.
 - [#6086](https://github.com/firecracker-microvm/firecracker/pull/6086),
   [#6143](https://github.com/firecracker-microvm/firecracker/pull/6143): Fixed a
   deadlock in the logger: a signal handler that logs while the interrupted

src/vmm/src/devices/virtio/block/device.rs

@@ -129,42 +129,42 @@ impl VirtioDevice for Block {
     fn avail_features(&self) -> u64 {
         match self {
             Self::Virtio(b) => b.avail_features,
-            Self::VhostUser(b) => b.avail_features,
+            Self::VhostUser(b) => b.avail_features(),
         }
     }
 
     fn acked_features(&self) -> u64 {
         match self {
             Self::Virtio(b) => b.acked_features,
-            Self::VhostUser(b) => b.acked_features,
+            Self::VhostUser(b) => b.acked_features(),
         }
     }
 
     fn set_acked_features(&mut self, acked_features: u64) {
         match self {
             Self::Virtio(b) => b.acked_features = acked_features,
-            Self::VhostUser(b) => b.acked_features = acked_features,
+            Self::VhostUser(b) => b.set_acked_features(acked_features),
         }
     }
 
     fn queues(&self) -> &[Queue] {
         match self {
             Self::Virtio(b) => &b.queues,
-            Self::VhostUser(b) => &b.queues,
+            Self::VhostUser(b) => b.queues(),
         }
     }
 
     fn queues_mut(&mut self) -> &mut [Queue] {
         match self {
             Self::Virtio(b) => &mut b.queues,
-            Self::VhostUser(b) => &mut b.queues,
+            Self::VhostUser(b) => b.queues_mut(),
         }
     }
 
     fn queue_events(&self) -> &[EventFd] {
         match self {
             Self::Virtio(b) => &b.queue_evts,
-            Self::VhostUser(b) => &b.queue_evts,
+            Self::VhostUser(b) => b.queue_events(),
         }
     }
 
@@ -203,7 +203,7 @@ impl VirtioDevice for Block {
     fn is_activated(&self) -> bool {
         match self {
             Self::Virtio(b) => b.device_state.is_activated(),
-            Self::VhostUser(b) => b.device_state.is_activated(),
+            Self::VhostUser(b) => b.is_activated(),
         }
     }