Use Btrfs#btrfs_subvolume_mount_point when setting Btrfs 'ro'

src/lib/installation/clients/umount_finish.rb

@@ -411,6 +411,9 @@ def set_btrfs_defaults_as_ro
       ro_btrfs_filesystems.each { |f| default_subvolume_as_ro(f) }
     end
 
+    # [String] Name used by btrfs tools to name the filesystem tree.
+    BTRFS_FS_TREE = "(FS_TREE)".freeze
+
     # Set the "read-only" property for the root subvolume.
     # This has to be done as long as the target root filesystem is still
     # mounted.
@@ -421,18 +424,13 @@ def default_subvolume_as_ro(fs)
         "btrfs", "subvolume", "get-default", fs.mount_point.path, stdout: :capture
       )
       default_subvolume = output.strip.split.last
-
       # no btrfs_default_subvolume and no snapshots
-      default_subvolume = "" if default_subvolume == "(FS_TREE)"
-
-      if !fs.subvolumes_prefix.empty?
-        default_subvolume = default_subvolume.sub(fs.subvolumes_prefix, "")
-      end
+      default_subvolume = "" if default_subvolume == BTRFS_FS_TREE
 
-      default_subvolume = Pathname.new(fs.mount_point.path).join(default_subvolume).to_s
+      subvolume_path = fs.btrfs_subvolume_mount_point(default_subvolume)
 
-      log.info("Setting root subvol read-only property on #{default_subvolume}")
-      Yast::Execute.on_target("btrfs", "property", "set", default_subvolume, "ro", "true")
+      log.info("Setting root subvol read-only property on #{subvolume_path}")
+      Yast::Execute.on_target("btrfs", "property", "set", subvolume_path, "ro", "true")
     end
   end
 end

test/lib/clients/umount_finish_test.rb

@@ -43,6 +43,8 @@
           let(:get_default) { "ID 276 gen 1172 top level 275 path .snapshots/1/snapshot\n" }
 
           it "sets 'ro' property to true on the snapshot" do
+            expect(root_fs).to receive(:btrfs_subvolume_mount_point)
+              .with(".snapshots/1/snapshot").and_return("/.snapshots/1/snapshot")
             expect(Yast::Execute).to receive(:on_target)
               .with("btrfs", "property", "set", "/.snapshots/1/snapshot", "ro", "true")
             client.set_btrfs_defaults_as_ro
@@ -53,6 +55,8 @@
           let(:get_default) { "ID 5 (FS_TREE)\n" }
 
           it "sets 'ro' property to true on the mount point" do
+            expect(root_fs).to receive(:btrfs_subvolume_mount_point)
+              .with("").and_return("/")
             expect(Yast::Execute).to receive(:on_target)
               .with("btrfs", "property", "set", "/", "ro", "true")
             client.set_btrfs_defaults_as_ro
@@ -67,6 +71,8 @@
           let(:get_default) { "ID 276 gen 1172 top level 275 path @/.snapshots/1/snapshot\n" }
 
           it "sets 'ro' property to true on the snapshot" do
+            expect(root_fs).to receive(:btrfs_subvolume_mount_point)
+              .with("@/.snapshots/1/snapshot").and_return("/.snapshots/1/snapshot")
             expect(Yast::Execute).to receive(:on_target)
               .with("btrfs", "property", "set", "/.snapshots/1/snapshot", "ro", "true")
             client.set_btrfs_defaults_as_ro
@@ -77,6 +83,8 @@
           let(:get_default) { "ID 276 gen 1172 top level 275 path @\n" }
 
           it "sets 'ro' property to true on the mount point" do
+            expect(root_fs).to receive(:btrfs_subvolume_mount_point)
+              .with("@").and_return("/")
             expect(Yast::Execute).to receive(:on_target)
               .with("btrfs", "property", "set", "/", "ro", "true")
             client.set_btrfs_defaults_as_ro
@@ -95,6 +103,8 @@
         end
 
         it "sets 'ro' property to true on the mount point" do
+          expect(root_fs).to receive(:btrfs_subvolume_mount_point)
+            .with("").and_return("/home")
           expect(Yast::Execute).to receive(:on_target)
             .with("btrfs", "property", "set", "/home", "ro", "true")
           client.set_btrfs_defaults_as_ro