Move the PuzzleFS Image Rootfs at the beginning of the layers array i…

…n the Image Manifest

Let's make the PuzzleFS image rootfs the first layer so it's easy to
find. The LXC oci template also looks at the first layer in the array to
identify the image type (see getlayermediatype) [1]

[1] lxc/lxc@1a2da75

Signed-off-by: Ariel Miculas-Trif <[email protected]>

puzzlefs-lib/src/oci.rs

@@ -121,7 +121,16 @@ impl Image {
         } else {
             self.0.dir.write(&path, final_data)?;
         }
-        image_manifest.layers_mut().push(descriptor.clone());
+
+        // Let's make the PuzzleFS image rootfs the first layer so it's easy to find
+        // The LXC oci template also looks at the first layer in the array to identify the image
+        // type (see getlayermediatype):
+        // https://github.com/lxc/lxc/commit/1a2da75b6e8431f3530ebd3f75442d3bd5eec5e2
+        if media_type.name() == PUZZLEFS_ROOTFS {
+            image_manifest.layers_mut().insert(0, descriptor.clone());
+        } else {
+            image_manifest.layers_mut().push(descriptor.clone());
+        }
         Ok((descriptor, fs_verity_digest, compressed_blob))
     }