Added checkpoint support to libnm in branch bg/libnm-checkpoint-rh1496739.

If needed, nmcli support can be added later, but at the moment it does not seem necessary as the checkpoint functionality is likely to be used programmatically rather than from command line. In the branch there is a short python example that  can be used to manage checkpoints from command line.

> core: turn NMCheckpointManager into a GObject

I am not convinced about GObject. GObject make sense for stuff we export on D-Bus (because our D-Bus glue is GObject based).
Otherwise, it's often overkill: more lines of code, slower, and provides for flexibility/use-cases that are never used.

Note how NMManager is really strongly related to NMCheckpointManager. The point is not to have both types used independently (there is no need for that). The raison d'etre of NMCheckpointManager is to move a portion of the code out of nm-manager.c.
Yes, NMManager and NMCheckpointManager are tightly coupled, but is that wrong? Their interface between each other is still small and contained.

E.g. nobody except NMManager is ever going to subscribe to "notifiy::checkpoints". If all you want is to get a notification _checkpoint_mgr_changed(), you could just as well pass a callback

  priv->checkpoint_mgr = nm_checkpoint_manager_new (self,
                                                    _checkpoint_mgr_changed);

You a bit more coupled, even just do

  priv->checkpoint_mgr = \
         nm_checkpoint_manager_new (self,                                                                 
                                    obj_properties[PROP_CHECKPOINTS]);

and then in checkpoint-manager, do

void _notify_checkpoints(NMCheckpointManager *self) {
  g_object_notify_by_pspec (_GET_MANAGER (self), self->_checkpoint_pspec);
}



> checkpoint: track checkpoints in a list
    
     g_hash_table_iter_init (&iter, priv->checkpoints);
-    while (g_hash_table_iter_next (&iter, NULL, (gpointer *) &checkpoint)) {
-         ts = nm_checkpoint_get_rollback_ts (checkpoint);
+    while (g_hash_table_iter_next (&iter, NULL, (gpointer *) &item)) {
+         ts = nm_checkpoint_get_rollback_ts (item->checkpoint);

now, that you have a CList, let's iterate the CList instead of the GHashTable.

pushed two fixups.

lgtm now

(In reply to Thomas Haller from comment #5)
> pushed two fixups.

Thanks, merged to master:

https://cgit.freedesktop.org/NetworkManager/NetworkManager/commit/?id=f02df2c2ca0a57696840e80c647b4d8176ea449b

Beniamino, do we have some sample script anywhere in the examples or so?

(In reply to Vladimir Benes from comment #8)
> Beniamino, do we have some sample script anywhere in the examples or so?

Hi, this uses libnm through gobject-introspection:

https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/examples/python/gi/checkpoint.py?id=cd79a22d186e2bd465a84bd9340a8971f4542090

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:3207