sq with vhost_user_blk

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

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

@@ -137,23 +137,29 @@ impl VhostUserBlock {
 
         let requested_protocol_features = VhostUserProtocolFeatures::CONFIG;
 
-        let mut vu = VhostUserHandle::new(&config.socket, NUM_QUEUES)
+        let mut vu_handle = VhostUserHandle::new(&config.socket, NUM_QUEUES)
             .map_err(VhostUserBlockError::VhostUser)?;
-        let (acked_features, acked_protocol_features) = vu
+        let (acked_features, acked_protocol_features) = vu_handle
             .negotiate_features(requested_features, requested_protocol_features)
             .map_err(VhostUserBlockError::VhostUser)?;
 
-        // Buffer only used for size checks.
-        let buffer = [0u8; BLOCK_CONFIG_SPACE_SIZE as usize];
-        let (_, config_space) = vu
-            .socket_handle()
-            .get_config(
-                VHOST_USER_CONFIG_OFFSET,
-                BLOCK_CONFIG_SPACE_SIZE,
-                VhostUserConfigFlags::WRITABLE,
-                &buffer,
-            )
-            .map_err(VhostUserBlockError::Vhost)?;
+        // Get config from backend if CONFIG is acked or use empty buffer.
+        let config_space = if acked_protocol_features & VhostUserProtocolFeatures::CONFIG != 0 {
+            // This buffer is read only. Ask vhost implementation why.
+            let buffer = [0u8; BLOCK_CONFIG_SPACE_SIZE as usize];
+            let (_, new_config_space) = vu_handle
+                .vu
+                .get_config(
+                    VHOST_USER_CONFIG_OFFSET,
+                    BLOCK_CONFIG_SPACE_SIZE,
+                    VhostUserConfigFlags::WRITABLE,
+                    &buffer,
+                )
+                .map_err(VhostUserBlockError::Vhost)?;
+            new_config_space
+        } else {
+            vec![]
+        };
 
         let activate_evt =
             EventFd::new(libc::EFD_NONBLOCK).map_err(VhostUserBlockError::EventFd)?;
@@ -187,7 +193,7 @@ impl VhostUserBlock {
             read_only,
             root_device: config.is_root_device,
 
-            vu_handle: vu,
+            vu_handle,
             vu_acked_protocol_features: acked_protocol_features,
         })
     }