bib: set filesystem type for all filesystems to match rootfs

Iterate over each Mountable in the partition table (each filesystem) and
change the filesystem type to match the rootfs, with two exceptions:
- /boot/efi is never changed
- /boot is not changed when rootfs is btrfs

Do this *after* the partition table with the customizations has been
generated, so that all filesystems in the final partition table are
properly set.

This also fixes osbuild#407.

Author: achilleas-k

cmd/bootc-image-builder/image.go

@@ -173,25 +173,37 @@ func updateFilesystemSizes(fsCustomizations []blueprint.FilesystemCustomization,
 	return updated
 }
 
-// setRootfsType sets the filesystem type for the mountable entity with target
-// '/'.
-func setRootfsType(pt *disk.PartitionTable, rootfs string) error {
+// setFSTypes sets the filesystem types for all mountable entities to match the
+// selected rootfs type.
+// If rootfs is 'btrfs', the function will keep '/boot' to its default.
+func setFSTypes(pt *disk.PartitionTable, rootfs string) error {
 	if rootfs == "" {
 		return fmt.Errorf("root filesystem type is empty")
 	}
-	rootMountable := pt.FindMountable("/")
-	if rootMountable == nil {
-		// this should be caught by tests and never actually happen but let's
-		// print the entire partition table in case it does due to a
-		// programming mistake or bug to make troubleshooting easier
-		return fmt.Errorf("internal partition table does not define a root filesystem: %+v", pt)
-	}
-	rootFsEntity, isfs := rootMountable.(*disk.Filesystem)
-	if !isfs {
-		return fmt.Errorf("the root mountable disk entity of the base partition table is not an ordinary filesystem but %T", rootMountable)
-	}
-	rootFsEntity.Type = rootfs
-	return nil
+
+	return pt.ForEachMountable(func(mnt disk.Mountable, _ []disk.Entity) error {
+		switch mnt.GetMountpoint() {
+		case "/boot/efi":
+			// never change the efi partition's type
+			return nil
+		case "/boot":
+			// change only if we're not doing btrfs
+			if rootfs == "btrfs" {
+				return nil
+			}
+			fallthrough
+		default:
+			switch elem := mnt.(type) {
+			case *disk.Filesystem:
+				elem.Type = rootfs
+			case *disk.BtrfsSubvolume:
+				// nothing to do
+			default:
+				return fmt.Errorf("the mountable disk entity for %q of the base partition table is not an ordinary filesystem but %T", mnt.GetMountpoint(), mnt)
+			}
+			return nil
+		}
+	})
 }
 
 func manifestForDiskImage(c *ManifestConfig, rng *rand.Rand) (*manifest.Manifest, error) {
@@ -270,14 +282,15 @@ func manifestForDiskImage(c *ManifestConfig, rng *rand.Rand) (*manifest.Manifest
 		return nil, err
 	}
 	fsCustomizations := updateFilesystemSizes(customizations.GetFilesystems(), c.RootfsMinsize)
-	if err := setRootfsType(&basept, c.RootFSType); err != nil {
-		return nil, fmt.Errorf("error setting root filesystem type: %w", err)
-	}
 
 	pt, err := disk.NewPartitionTable(&basept, fsCustomizations, DEFAULT_SIZE, partitioningMode, nil, rng)
 	if err != nil {
 		return nil, err
 	}
+
+	if err := setFSTypes(pt, c.RootFSType); err != nil {
+		return nil, fmt.Errorf("error setting root filesystem type: %w", err)
+	}
 	img.PartitionTable = pt
 
 	// For the bootc-disk image, the filename is the basename and the extension