Groundwork for oximeter instance vCPU metrics

- Adds the silo and project IDs to the instance-ensure request from
  Nexus to the sled-agent. These are used as fields on the
  instance-related statistics. This metadata is currently unused, but
  will be forwarded to Propolis in the instance-ensure request once the
  server is updated to accept it.
- Defines a `VirtualMachine` oximeter target and `VcpuUsage` metric. The
  latter has a `state` field which corresponds to the named kstats
  published by the hypervisor that accumulate the time spent in a number
  of vCPU microstates. The combination of these should allow us to
  aggregate or break down vCPU usage by silo, project, instance, vCPU
  ID, and CPU state. Adds some simple mocks and tests for these.
- Adds more fine-grained feature flags to the `oximeter-instruments`
  crate.

nexus/src/app/instance.rs

@@ -1146,6 +1146,21 @@ impl super::Nexus {
             .map(|ssh_key| ssh_key.public_key)
             .collect::<Vec<String>>();
 
+        // Construct instance metadata used to track its statistics.
+        //
+        // This current means fetching the current silo ID, since we have all
+        // the other metadata already.
+        let silo_id = self
+            .current_silo_lookup(opctx)?
+            .lookup_for(authz::Action::Read)
+            .await?
+            .0
+            .id();
+        let metadata = sled_agent_client::types::InstanceMetadata {
+            silo_id,
+            project_id: db_instance.project_id,
+        };
+
         // Ask the sled agent to begin the state change.  Then update the
         // database to reflect the new intermediate state.  If this update is
         // not the newest one, that's fine.  That might just mean the sled agent
@@ -1189,6 +1204,7 @@ impl super::Nexus {
                         PROPOLIS_PORT,
                     )
                     .to_string(),
+                    metadata,
                 },
             )
             .await

openapi/sled-agent.json

@@ -4589,6 +4589,14 @@
               }
             ]
           },
+          "metadata": {
+            "description": "Metadata used to track instance statistics.",
+            "allOf": [
+              {
+                "$ref": "#/components/schemas/InstanceMetadata"
+              }
+            ]
+          },
           "propolis_addr": {
             "description": "The address at which this VMM should serve a Propolis server API.",
             "type": "string"
@@ -4610,6 +4618,7 @@
         "required": [
           "hardware",
           "instance_runtime",
+          "metadata",
           "propolis_addr",
           "propolis_id",
           "vmm_runtime"
@@ -4741,6 +4750,24 @@
           "snapshot_id"
         ]
       },
+      "InstanceMetadata": {
+        "description": "Metadata used to track statistics about an instance.",
+        "type": "object",
+        "properties": {
+          "project_id": {
+            "type": "string",
+            "format": "uuid"
+          },
+          "silo_id": {
+            "type": "string",
+            "format": "uuid"
+          }
+        },
+        "required": [
+          "project_id",
+          "silo_id"
+        ]
+      },
       "InstanceMigrationSourceParams": {
         "description": "Instance runtime state to update for a migration.",
         "type": "object",

oximeter/instruments/Cargo.toml

@@ -5,27 +5,49 @@ edition = "2021"
 license = "MPL-2.0"
 
 [dependencies]
-cfg-if.workspace = true
-chrono.workspace = true
-dropshot.workspace = true
-futures.workspace = true
+cfg-if = { workspace = true, optional = true }
+chrono = { workspace = true, optional = true }
+dropshot = { workspace = true, optional = true }
+futures = { workspace = true, optional = true }
 http = { workspace = true, optional = true }
-oximeter.workspace = true
-slog.workspace = true
-tokio.workspace = true
-thiserror.workspace = true
-uuid.workspace = true
-omicron-workspace-hack.workspace = true
+oximeter = { workspace = true, optional = true }
+slog = { workspace = true, optional = true }
+tokio = { workspace = true, optional = true }
+thiserror = { workspace = true, optional = true }
+uuid = { workspace = true, optional = true }
+omicron-workspace-hack = { workspace = true, optional = true }
 
 [features]
-default = ["http-instruments", "kstat"]
-http-instruments = ["http"]
-kstat = ["kstat-rs"]
+default = ["http-instruments", "datalink", "virtual-machine"]
+http-instruments = [
+    "dep:chrono",
+    "dep:dropshot",
+    "dep:futures",
+    "dep:http",
+    "dep:omicron-workspace-hack",
+    "dep:oximeter",
+    "dep:uuid"
+]
+kstat = [
+    "dep:cfg-if",
+    "dep:chrono",
+    "dep:futures",
+    "dep:kstat-rs",
+    "dep:omicron-workspace-hack",
+    "dep:oximeter",
+    "dep:slog",
+    "dep:tokio",
+    "dep:thiserror",
+    "dep:uuid"
+]
+datalink = ["kstat"]
+virtual-machine = ["kstat"]
 
 [dev-dependencies]
 rand.workspace = true
 slog-async.workspace = true
 slog-term.workspace = true
+oximeter.workspace = true
 
 [target.'cfg(target_os = "illumos")'.dependencies]
 kstat-rs = { workspace = true, optional = true }

oximeter/instruments/src/kstat/mod.rs

@@ -87,8 +87,11 @@ use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::time::Duration;
 
+#[cfg(any(feature = "datalink", test))]
 pub mod link;
 mod sampler;
+#[cfg(any(feature = "virtual-machine", test))]
+pub mod virtual_machine;
 
 pub use sampler::CollectionDetails;
 pub use sampler::ExpirationBehavior;