podstorage: fsync storage root before and after creating .bootc_labeled

Sync the storage root directory after relabeling to ensure the label
writes are durable before creating the stamp file, and again after
creating and labeling the stamp file to persist the directory entry.
This avoids a crash leaving the system in a state where the stamp
exists but the relabeling writes were lost.

Closes: #1210
Signed-off-by: Andrew Dunn <andrew@dunn.dev>

Author: andrewdunndev

crates/lib/src/podstorage.rs

@@ -235,6 +235,14 @@ impl CStorage {
         )
         .context("labeling storage root")?;
 
+        // fsync so relabel writes are durable before creating the stamp file
+        rustix::fs::fsync(
+            self.storage_root
+                .reopen_as_ownedfd()
+                .context("Reopening as owned fd")?,
+        )
+        .context("fsync")?;
+
         self.storage_root.create(LABELED)?;
 
         // Label the stamp file itself to match the storage directory context
@@ -247,6 +255,14 @@ impl CStorage {
         )
         .context("labeling stamp file")?;
 
+        // fsync to persist the stamp file entry
+        rustix::fs::fsync(
+            self.storage_root
+                .reopen_as_ownedfd()
+                .context("Reopening as owned fd")?,
+        )
+        .context("fsync")?;
+
         Ok(())
     }