phd: better method for referencing a disk from a VmSpec

Author: gjcolombo

phd-tests/framework/src/test_vm/spec.rs

@@ -34,13 +34,13 @@ pub struct VmSpec {
 }
 
 impl VmSpec {
-    /// Yields an array of handles to this VM's Crucible disks.
-    pub fn get_crucible_disks(&self) -> Vec<Arc<dyn disk::DiskConfig>> {
+    pub fn get_disk_by_device_name(
+        &self,
+        name: &str,
+    ) -> Option<&Arc<dyn disk::DiskConfig>> {
         self.disk_handles
             .iter()
-            .filter(|d| d.as_crucible().is_some())
-            .cloned()
-            .collect()
+            .find(|disk| disk.device_name().as_str() == name)
     }
 
     /// Update the Crucible backend specs in the instance spec to match the

phd-tests/tests/src/crucible/smoke.rs

@@ -95,8 +95,9 @@ async fn vcr_replace_test(ctx: &Framework) {
     // necessary because Crucible doesn't permit VCR replacements for volumes
     // whose read-only parents are local files (which is true for artifact-based
     // Crucible disks).
+    const DATA_DISK_NAME: &str = "vcr-replacement-target";
     config.data_disk(
-        "vcr-replacement-target",
+        DATA_DISK_NAME,
         DiskSource::Blank(1024 * 1024 * 1024),
         DiskInterface::Nvme,
         DiskBackend::Crucible {
@@ -107,8 +108,9 @@ async fn vcr_replace_test(ctx: &Framework) {
     );
 
     let spec = config.vm_spec(ctx).await?;
-    let disks = spec.get_crucible_disks();
-    let disk = disks[0].as_crucible().unwrap();
+    let disk_hdl =
+        spec.get_disk_by_device_name(DATA_DISK_NAME).cloned().unwrap();
+    let disk = disk_hdl.as_crucible().unwrap();
 
     let mut vm = ctx.spawn_vm_with_spec(spec, None).await?;
     vm.launch().await?;