Implement the reference counter logic in core uprobe. User will be
able to use it from trace_uprobe as well as from kernel module. New
trace_uprobe definition with reference counter will now be:

    <path>:<offset>[(ref_ctr_offset)]

where ref_ctr_offset is an optional field. For kernel module, new
variant of uprobe_register() has been introduced:

    uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer)

Sorry for bringing this again, but I would actually think the ref_ctr is
a consumer property. i.e the ref_ctr_offset should be part of
uprobe_consumer.

The advantages of doing that would be
1. Dont need to expose uprobe structure and just update our
uprobe_consumer which is already an exported structure.
- Exporting uprobe structure would expose some of our internal
  implementation details, basically reduce the freedom of changing stuff
  internally.
- we came up with uprobe_arch for the parts that we wanted to expose
  to archs. exposing uprobe and uprobe_arch looks weird.

2. ref_ctr_offset is necessarily a consumer property, its not a uprobe
property at all.

3. We dont need to change/add new uprobe_register functions.

The way I look at it is.

Based on the ref_ctr_offset field in consumer, we update_ref_ctr()
around install_breakpoint/remove_breakpoint.

+static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
+{
+	struct delayed_uprobe *du;
+
+	if (delayed_uprobe_check(uprobe, mm))
+		return 0;
+
+	du  = kzalloc(sizeof(*du), GFP_KERNEL);
+	if (!du)
+		return -ENOMEM;
+
+	du->uprobe = uprobe;
+	du->mm = mm;
+	list_add(&du->list, &delayed_uprobe_list);
+	return 0;
+}
+

If I understood the delayed_uprobe stuff, its when we could insert a
breakpoint but the vma that has the ref_ctr_offset is not loaded. Is
that correct?

-- 
2.14.4