Comment # 6 on bug 1177419 from Thomas Blume

Checking the dbus information between the rw versus ro setup of loop0, I can
see indeed a quite significant difference:

-->
kvm110:/tmp/bsc1177419 # diff -Naur loop0-rw-dbus.txt loop0-ro-dbus.txt 
--- loop0-rw-dbus.txt    2020-10-08 18:00:28.739927763 +0200
+++ loop0-ro-dbus.txt    2020-10-08 17:59:54.002230687 +0200
@@ -29,25 +29,6 @@
     signals:
     properties:
   };
-  interface org.freedesktop.UDisks2.Filesystem {
-    methods:
-      SetLabel(in  s label,
-               in  a{sv} options);
-      Mount(in  a{sv} options,
-            out s mount_path);
-      Unmount(in  a{sv} options);
-      Resize(in  t size,
-             in  a{sv} options);
-      Check(in  a{sv} options,
-            out b consistent);
-      Repair(in  a{sv} options,
-             out b repaired);
-      TakeOwnership(in  a{sv} options);
-    signals:
-    properties:
-      readonly aay MountPoints = [];
-      readonly t Size = 0;
-  };
   interface org.freedesktop.UDisks2.Loop {
     methods:
       Delete(in  a{sv} options);
@@ -55,7 +36,7 @@
                    in  a{sv} options);
     signals:
     properties:
-      readonly ay BackingFile = b'/tmp/bsc1177419/udisk_test.iso';
+      readonly ay BackingFile = b'';
       readonly b Autoclear = false;
       readonly u SetupByUID = 0;
   };
@@ -86,19 +67,19 @@
     properties:
       readonly ay Device = b'/dev/loop0';
       readonly ay PreferredDevice = b'/dev/loop0';
-      readonly aay Symlinks = [b'/dev/disk/by-label/CDROM',
b'/dev/disk/by-uuid/2020-10-08-10-55-22-25'];
+      readonly aay Symlinks = [];
       readonly t DeviceNumber = 1792;
       readonly s Id = '';
-      readonly t Size = 358400;
-      readonly b ReadOnly = false;
+      readonly t Size = 0;
+      readonly b ReadOnly = true;
       readonly o Drive = '/';
       readonly o MDRaid = '/';
       readonly o MDRaidMember = '/';
-      readonly s IdUsage = 'filesystem';
-      readonly s IdType = 'iso9660';
+      readonly s IdUsage = '';
+      readonly s IdType = '';
       readonly s IdVersion = '';
-      readonly s IdLabel = 'CDROM';
-      readonly s IdUUID = '2020-10-08-10-55-22-25';
+      readonly s IdLabel = '';
+      readonly s IdUUID = '';
       readonly a(sa{sv}) Configuration = [];
       readonly o CryptoBackingDevice = '/';
       readonly b HintPartitionable = true;
@@ -111,4 +92,3 @@
       readonly as UserspaceMountOptions = [];
   };
 };
-
--<

So, the backing file property is empty.
The udev monitor shows that there are no uevents triggered in ro case.