Write per-VM log through a tracing layer

README.md

@@ -205,7 +205,9 @@ A dash (`-`) means no sample is available for that field.
 
 The per-VM log also records `event=vm_added` when the daemon starts tracking
 the VM and `event=vm_removed reason=<not_discovered|refresh_failed>` when it
-stops.
+stops. Every other log event that names the VM in a `vm` field, such as scaling
+decisions, blocked or failed scale operations, and backend errors, is copied to
+the VM's file as its message followed by its remaining `key=value` fields.
 
 ### Aggregate line
 

src/backends/qemu/client.rs

@@ -103,7 +103,7 @@ impl QemuInstanceClient {
             if let Err(del_err) = self.client.del_io_thread(&new_id).await {
                 tracing::debug!(
                     target: "qemu",
-                    uuid = %self.uuid,
+                    vm = %self.uuid,
                     iothread = %new_id,
                     "rollback object-del after set-mapping failure: {del_err}"
                 );
@@ -133,7 +133,7 @@ impl QemuInstanceClient {
         if let Err(e) = self.client.del_io_thread(&doomed).await {
             tracing::warn!(
                 target: "qemu",
-                uuid = %self.uuid,
+                vm = %self.uuid,
                 iothread = %doomed,
                 error = ?e,
                 "object-del failed; will retry next tick"
@@ -159,7 +159,7 @@ impl QemuInstanceClient {
         if thread_count == 1 {
             tracing::debug!(
                 target: "qemu",
-                uuid = %self.uuid,
+                vm = %self.uuid,
                 "using minimal fallback snapshot without cached topology"
             );
         }
@@ -170,7 +170,7 @@ impl QemuInstanceClient {
             Err(e) => {
                 tracing::debug!(
                     target: "qemu",
-                    uuid = %self.uuid,
+                    vm = %self.uuid,
                     error = ?e,
                     "query-blockstats failed"
                 );
@@ -239,7 +239,7 @@ impl InstanceClient for QemuInstanceClient {
                 if should_warn {
                     tracing::warn!(
                         target: "qemu",
-                        uuid = %self.uuid,
+                        vm = %self.uuid,
                         "QMP command x-query-prometheus-metrics unsupported; using fallback snapshot"
                     );
                 }
@@ -305,7 +305,7 @@ impl InstanceClient for QemuInstanceClient {
             Err(e) => {
                 tracing::debug!(
                     target: "qemu",
-                    uuid = %self.uuid,
+                    vm = %self.uuid,
                     error = ?e,
                     "query-blockstats failed"
                 );

src/backends/qemu/libvirt.rs

@@ -108,7 +108,7 @@ impl LibvirtConn {
                     Err(e) => {
                         tracing::debug!(
                             target: "qemu",
-                            uuid = %uuid,
+                            vm = %uuid,
                             error = ?e,
                             "libvirt: skip vm (xml fetch)"
                         );

src/backends/qemu/mod.rs

@@ -186,15 +186,15 @@ impl Backend for QemuBackend {
                 Ok(_) => {
                     tracing::warn!(
                         target: "qemu",
-                        %uuid,
+                        vm = %uuid,
                         "libvirt reported zero maximum vCPUs; skipping VM"
                     );
                     continue;
                 }
                 Err(error) => {
                     tracing::warn!(
                         target: "qemu",
-                        %uuid,
+                        vm = %uuid,
                         %error,
                         "failed to read maximum vCPU count; skipping VM"
                     );