virtio-devices: vhost_user: Adapt state() to return Result

This is a refactoring step in preparation for fetching backend device
state via SET_DEVICE_STATE_FD which can fail.

Signed-off-by: Rob Bradford <rbradford@meta.com>

virtio-devices/src/vhost_user/blk.rs

@@ -191,7 +191,7 @@ impl Blk {
         })
     }
 
-    fn state(&self) -> State {
+    fn state(&self) -> std::result::Result<State, MigratableError> {
         self.vu_common.state(&self.common, self.config)
     }
 }
@@ -367,7 +367,7 @@ impl Snapshottable for Blk {
     }
 
     fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
-        self.vu_common.snapshot(&self.state())
+        self.vu_common.snapshot(&self.state()?)
     }
 }
 impl Transportable for Blk {}

virtio-devices/src/vhost_user/fs.rs

@@ -200,7 +200,7 @@ impl Fs {
         })
     }
 
-    fn state(&self) -> State {
+    fn state(&self) -> std::result::Result<State, MigratableError> {
         self.vu_common.state(&self.common, self.config)
     }
 }
@@ -377,7 +377,7 @@ impl Snapshottable for Fs {
     }
 
     fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
-        self.vu_common.snapshot(&self.state())
+        self.vu_common.snapshot(&self.state()?)
     }
 }
 impl Transportable for Fs {}

virtio-devices/src/vhost_user/generic_vhost_user.rs

@@ -156,7 +156,7 @@ since the backend only supports {backend_num_queues}\n",
         })
     }
 
-    fn state(&self) -> State {
+    fn state(&self) -> std::result::Result<State, MigratableError> {
         self.vu_common.state(&self.common, ())
     }
 
@@ -396,7 +396,7 @@ impl Snapshottable for GenericVhostUser {
     }
 
     fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
-        self.vu_common.snapshot(&self.state())
+        self.vu_common.snapshot(&self.state()?)
     }
 }
 impl Transportable for GenericVhostUser {}

virtio-devices/src/vhost_user/mod.rs

@@ -457,15 +457,21 @@ impl VhostUserCommon {
         Ok(())
     }
 
-    pub fn state<C: Default>(&self, common: &crate::VirtioCommon, config: C) -> VhostUserState<C> {
+    pub fn state<C: Default>(
-        VhostUserState {
+        &self,
+        common: &crate::VirtioCommon,
+        config: C,
+    ) -> std::result::Result<VhostUserState<C>, MigratableError> {
+        let state = VhostUserState {
             avail_features: common.avail_features,
             acked_features: common.acked_features,
             config,
             acked_protocol_features: self.acked_protocol_features,
             vu_num_queues: self.vu_num_queues,
             ..Default::default()
-        }
+        };
+
+        Ok(state)
     }
 
     pub fn snapshot<T>(&mut self, state: &T) -> std::result::Result<Snapshot, MigratableError>

virtio-devices/src/vhost_user/net.rs

@@ -220,7 +220,7 @@ impl Net {
         })
     }
 
-    fn state(&self) -> State {
+    fn state(&self) -> std::result::Result<State, MigratableError> {
         self.vu_common.state(&self.common, self.config)
     }
 }
@@ -425,7 +425,7 @@ impl Snapshottable for Net {
     }
 
     fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
-        self.vu_common.snapshot(&self.state())
+        self.vu_common.snapshot(&self.state()?)
     }
 }
 impl Transportable for Net {}