virtio-fs: Deprecate the DAX feature

Disable the DAX feature from the virtio-fs implementation as the feature
is still not stable. The feature is deprecated, meaning the 'dax'
parameter will be removed in about 2 releases cycles.

In the meantime, the parameter value is ignored and forced to be
disabled.

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

vmm/src/config.rs

@@ -1530,7 +1530,7 @@ fn default_fsconfig_queue_size() -> u16 {
 }
 
 fn default_fsconfig_dax() -> bool {
-    true
+    false
 }
 
 fn default_fsconfig_cache_size() -> u64 {
@@ -1635,6 +1635,15 @@ impl FsConfig {
             }
         }
 
+        if self.dax {
+            // TODO: Remove the dax parameter.
+            // Tracked by https://github.com/cloud-hypervisor/cloud-hypervisor/issues/3889
+            warn!(
+                "The experimental DAX feature is deprecated and will be \
+                removed in a future release. A request to enable it is ignored."
+            );
+        }
+
         Ok(())
     }
 }

vmm/src/device_manager.rs

@@ -2395,6 +2395,9 @@ impl DeviceManager {
             None
         };
 
+        // DAX is not supported, we override the config by disabling the option.
+        fs_cfg.dax = false;
+
         if let Some(fs_socket) = fs_cfg.socket.to_str() {
             let cache = if fs_cfg.dax {
                 let (cache_base, cache_size) = if let Some((base, size)) = cache_range {