Temporarily disable region snapshot replacement (#6728)

Until read-only region reference counting is implemented, region
snapshot replacement should be disabled - it is currently the only thing
that creates read-only regions.

Author: jmpesp

nexus/src/app/background/init.rs

@@ -778,7 +778,8 @@ impl BackgroundTasksInitializer {
                 "detect if region snapshots need replacement and begin the \
                 process",
             period: config.region_snapshot_replacement_start.period_secs,
-            task_impl: Box::new(RegionSnapshotReplacementDetector::new(
+            // XXX temporarily disabled, see oxidecomputer/omicron#6353
+            task_impl: Box::new(RegionSnapshotReplacementDetector::disabled(
                 datastore.clone(),
                 sagas.clone(),
             )),
@@ -794,10 +795,13 @@ impl BackgroundTasksInitializer {
             period: config
                 .region_snapshot_replacement_garbage_collection
                 .period_secs,
-            task_impl: Box::new(RegionSnapshotReplacementGarbageCollect::new(
-                datastore.clone(),
-                sagas.clone(),
-            )),
+            // XXX temporarily disabled, see oxidecomputer/omicron#6353
+            task_impl: Box::new(
+                RegionSnapshotReplacementGarbageCollect::disabled(
+                    datastore.clone(),
+                    sagas.clone(),
+                ),
+            ),
             opctx: opctx.child(BTreeMap::new()),
             watchers: vec![],
             activator: task_region_snapshot_replacement_garbage_collection,
@@ -809,10 +813,13 @@ impl BackgroundTasksInitializer {
                 "detect what volumes were affected by a region snapshot \
                 replacement, and run the step saga for them",
             period: config.region_snapshot_replacement_step.period_secs,
-            task_impl: Box::new(RegionSnapshotReplacementFindAffected::new(
-                datastore.clone(),
-                sagas.clone(),
-            )),
+            // XXX temporarily disabled, see oxidecomputer/omicron#6353
+            task_impl: Box::new(
+                RegionSnapshotReplacementFindAffected::disabled(
+                    datastore.clone(),
+                    sagas.clone(),
+                ),
+            ),
             opctx: opctx.child(BTreeMap::new()),
             watchers: vec![],
             activator: task_region_snapshot_replacement_step,
@@ -824,9 +831,10 @@ impl BackgroundTasksInitializer {
                 "complete a region snapshot replacement if all the steps are \
                 done",
             period: config.region_snapshot_replacement_finish.period_secs,
-            task_impl: Box::new(RegionSnapshotReplacementFinishDetector::new(
-                datastore,
-            )),
+            // XXX temporarily disabled, see oxidecomputer/omicron#6353
+            task_impl: Box::new(
+                RegionSnapshotReplacementFinishDetector::disabled(datastore),
+            ),
             opctx: opctx.child(BTreeMap::new()),
             watchers: vec![],
             activator: task_region_snapshot_replacement_finish,

nexus/src/app/background/tasks/region_snapshot_replacement_finish.rs

@@ -19,11 +19,17 @@ use std::sync::Arc;
 
 pub struct RegionSnapshotReplacementFinishDetector {
     datastore: Arc<DataStore>,
+    disabled: bool,
 }
 
 impl RegionSnapshotReplacementFinishDetector {
+    #[allow(dead_code)]
     pub fn new(datastore: Arc<DataStore>) -> Self {
-        RegionSnapshotReplacementFinishDetector { datastore }
+        RegionSnapshotReplacementFinishDetector { datastore, disabled: false }
+    }
+
+    pub fn disabled(datastore: Arc<DataStore>) -> Self {
+        RegionSnapshotReplacementFinishDetector { datastore, disabled: true }
     }
 
     async fn transition_requests_to_done(
@@ -153,6 +159,10 @@ impl BackgroundTask for RegionSnapshotReplacementFinishDetector {
         async move {
             let mut status = RegionSnapshotReplacementFinishStatus::default();
 
+            if self.disabled {
+                return json!(status);
+            }
+
             self.transition_requests_to_done(opctx, &mut status).await;
 
             json!(status)

nexus/src/app/background/tasks/region_snapshot_replacement_garbage_collect.rs

@@ -22,11 +22,28 @@ use std::sync::Arc;
 pub struct RegionSnapshotReplacementGarbageCollect {
     datastore: Arc<DataStore>,
     sagas: Arc<dyn StartSaga>,
+    disabled: bool,
 }
 
 impl RegionSnapshotReplacementGarbageCollect {
+    #[allow(dead_code)]
     pub fn new(datastore: Arc<DataStore>, sagas: Arc<dyn StartSaga>) -> Self {
-        RegionSnapshotReplacementGarbageCollect { datastore, sagas }
+        RegionSnapshotReplacementGarbageCollect {
+            datastore,
+            sagas,
+            disabled: false,
+        }
+    }
+
+    pub fn disabled(
+        datastore: Arc<DataStore>,
+        sagas: Arc<dyn StartSaga>,
+    ) -> Self {
+        RegionSnapshotReplacementGarbageCollect {
+            datastore,
+            sagas,
+            disabled: true,
+        }
     }
 
     async fn send_garbage_collect_request(
@@ -135,6 +152,10 @@ impl BackgroundTask for RegionSnapshotReplacementGarbageCollect {
             let mut status =
                 RegionSnapshotReplacementGarbageCollectStatus::default();
 
+            if self.disabled {
+                return json!(status);
+            }
+
             self.clean_up_region_snapshot_replacement_volumes(
                 opctx,
                 &mut status,

nexus/src/app/background/tasks/region_snapshot_replacement_start.rs

@@ -29,11 +29,20 @@ use std::sync::Arc;
 pub struct RegionSnapshotReplacementDetector {
     datastore: Arc<DataStore>,
     sagas: Arc<dyn StartSaga>,
+    disabled: bool,
 }
 
 impl RegionSnapshotReplacementDetector {
+    #[allow(dead_code)]
     pub fn new(datastore: Arc<DataStore>, sagas: Arc<dyn StartSaga>) -> Self {
-        RegionSnapshotReplacementDetector { datastore, sagas }
+        RegionSnapshotReplacementDetector { datastore, sagas, disabled: false }
+    }
+
+    pub fn disabled(
+        datastore: Arc<DataStore>,
+        sagas: Arc<dyn StartSaga>,
+    ) -> Self {
+        RegionSnapshotReplacementDetector { datastore, sagas, disabled: true }
     }
 
     async fn send_start_request(
@@ -237,6 +246,10 @@ impl BackgroundTask for RegionSnapshotReplacementDetector {
         async {
             let mut status = RegionSnapshotReplacementStartStatus::default();
 
+            if self.disabled {
+                return json!(status);
+            }
+
             self.create_requests_for_region_snapshots_on_expunged_disks(
                 opctx,
                 &mut status,

nexus/src/app/background/tasks/region_snapshot_replacement_step.rs

@@ -42,11 +42,28 @@ use std::sync::Arc;
 pub struct RegionSnapshotReplacementFindAffected {
     datastore: Arc<DataStore>,
     sagas: Arc<dyn StartSaga>,
+    disabled: bool,
 }
 
 impl RegionSnapshotReplacementFindAffected {
+    #[allow(dead_code)]
     pub fn new(datastore: Arc<DataStore>, sagas: Arc<dyn StartSaga>) -> Self {
-        RegionSnapshotReplacementFindAffected { datastore, sagas }
+        RegionSnapshotReplacementFindAffected {
+            datastore,
+            sagas,
+            disabled: false,
+        }
+    }
+
+    pub fn disabled(
+        datastore: Arc<DataStore>,
+        sagas: Arc<dyn StartSaga>,
+    ) -> Self {
+        RegionSnapshotReplacementFindAffected {
+            datastore,
+            sagas,
+            disabled: true,
+        }
     }
 
     async fn send_start_request(
@@ -435,6 +452,10 @@ impl BackgroundTask for RegionSnapshotReplacementFindAffected {
         async move {
             let mut status = RegionSnapshotReplacementStepStatus::default();
 
+            if self.disabled {
+                return json!(status);
+            }
+
             // Importantly, clean old steps up before finding affected volumes!
             // Otherwise, will continue to find the snapshot in volumes to
             // delete, and will continue to see conflicts in next function.