Re: [RFC] [PATCH] Multiple kprobes at an address redux (take4)

[Prasanna S Panchamukhi <prasanna at in dot ibm dot com>]

Ananth,

>+static int register_aggr_kprobe(struct kprobe *p)
>+{
>+	int ret = 0;
>+	unsigned long flags = 0;
>+	struct kprobe *old_p, *ap;
>+
>+	ap = kcalloc(1, sizeof(struct kprobe), GFP_KERNEL);
>+	if (!ap) 
>+		return -ENOMEM;
>+
>+	spin_lock_irqsave(&kprobe_lock, flags);
>+	old_p = get_kprobe(p->addr);
>+	if (old_p) {
>+		if (old_p->break_handler || p->break_handler) {
>+			ret = -EEXIST;
>+			goto free_ap;

In your design document and in the code above shows that
multiprobe feature is incompatable with jprobes.

If a user wants of insert a kprobe at the entry point and exit probe at a 
function exit, your patch addressing multiple handler feature is useful.

but usually users are interested in both jprobe at the entrypoint (to dump
arguments) and to dump return values using exit probe feature.

To do this user succeeds inserting a jprobe at the entrypoint,
but when the user tries to register the exit probe for the same function,
it fails.

exit probe feature needs to register a kprobe at the entrypoint and if
there is a jprobe at the entrypoint, it is bound to fail.

Your design limitation wont be helpful for users interested in jprobe and
exit point probe.

Are you planning to address this issue now ?

Also you need to add comments explaining about the new routines added
in your patch.

Thanks
Prasanna

-- 

Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@in.ibm.com>