Do not overwrite UUIDs, throw conflict on mismatch

sled-storage/src/manager.rs

@@ -28,6 +28,7 @@ use omicron_common::disk::{
 };
 use omicron_common::ledger::Ledger;
 use omicron_uuid_kinds::DatasetUuid;
+use omicron_uuid_kinds::GenericUuid;
 use slog::{error, info, o, warn, Logger};
 use std::collections::BTreeMap;
 use std::collections::HashSet;
@@ -999,17 +1000,11 @@ impl StorageManager {
         };
 
         if old_id != config.id {
-            // NOTE(https://github.com/oxidecomputer/omicron/issues/7265):
-            //
-            // This should potentially return a "UuidMismatch" error in the
-            // future, rather than overwriting the existing dataset UUID.
-            warn!(
-                log,
-                "Dataset UUID mismatch. Choosing to take new value.";
-                "old" => ?old_id,
-                "new" => ?config.id
-            );
-            return Ok(false);
+            return Err(Error::UuidMismatch {
+                name: config.name.full_name(),
+                old: old_id.into_untyped_uuid(),
+                new: config.id.into_untyped_uuid(),
+            });
         }
 
         let old_props = match SharedDatasetConfig::try_from(old_dataset) {