incremental image layer

Signed-off-by: Alex Chi <chi@neon.tech>

pageserver/src/tenant/layer_map.rs

@@ -703,6 +703,11 @@ impl LayerMap {
             frozen_layer.dump(verbose, ctx)?;
         }
 
+        println!("l0_deltas:");
+        for layer in &self.l0_delta_layers {
+            layer.dump(verbose, ctx)?;
+        }
+
         println!("historic_layers:");
         for layer in self.iter_historic_layers() {
             layer.dump(verbose, ctx)?;

pageserver/src/tenant/storage_layer/image_layer.rs

@@ -213,7 +213,11 @@ impl Layer for ImageLayer {
             reconstruct_state.img = Some((self.lsn, value));
             Ok(ValueReconstructResult::Complete)
         } else {
-            Ok(ValueReconstructResult::Missing)
+            if self.desc.is_incremental {
+                Ok(ValueReconstructResult::Continue)
+            } else {
+                Ok(ValueReconstructResult::Missing)
+            }
         }
     }