Subject: Re: [RFC PATCH v2 3/8] rethook: Add a generic return hook

From: Jiri Olsa <[email-masked]>
Date: Fri, 14 Jan 2022 16:18:13 +0100

On Thu, Jan 13, 2022 at 10:15:32PM +0900, Masami Hiramatsu wrote:
> On Thu, 13 Jan 2022 13:25:52 +0100
> Jiri Olsa <[email-masked]> wrote:
> 
> > On Wed, Jan 12, 2022 at 11:03:22PM +0900, Masami Hiramatsu wrote:
> > > Add a return hook framework which hooks the function
> > > return. Most of the idea came from the kretprobe, but
> > > this is independent from kretprobe.
> > > Note that this is expected to be used with other
> > > function entry hooking feature, like ftrace, fprobe,
> > > adn kprobes. Eventually this will replace the
> > > kretprobe (e.g. kprobe + rethook = kretprobe), but
> > > at this moment, this is just a additional hook.
> > 
> > this looks similar to the code kretprobe is using now
> 
> Yes, I've mostly re-typed the code :)
> 
> > would it make sense to incrementaly change current code to provide
> > this rethook interface? instead of big switch of current kretprobe
> > to kprobe + new rethook interface in future?
> 
> Would you mean modifying the kretprobe instance code to provide
> similar one, and rename it at some point?
> My original idea is to keep the current kretprobe code and build
> up the similar one, and switch to it at some point. Actually,
> I don't want to change the current kretprobe interface itself,
> but the backend will be changed. For example, current kretprobe
> has below interface.
> 
> struct kretprobe {
>         struct kprobe kp;
>         kretprobe_handler_t handler;
>         kretprobe_handler_t entry_handler;
>         int maxactive;
>         int nmissed;
>         size_t data_size;
>         struct freelist_head freelist;
>         struct kretprobe_holder *rph;
> };
> 
> My idea is switching it to below.
> 
> struct kretprobe {
>         struct kprobe kp;
>         kretprobe_handler_t handler;
>         kretprobe_handler_t entry_handler;
>         int maxactive;
>         int nmissed;
>         size_t data_size;
>         struct rethook *rethook;
> };

looks good, will this be a lot of changes?
could you include it in the patchset?

thanks,
jirka

> 
> Of course 'kretprobe_instance' may need to be changed...
> 
> struct kretprobe_instance {
> 	struct rethook_node;
> 	char data[];
> };
> 
> But even though, since there is 'get_kretprobe(ri)' wrapper, user
> will be able to access the 'struct kretprobe' from kretprobe_instance
> transparently.
> 
> Thank you,
> 
> 
> -- 
> Masami Hiramatsu <[email-masked]>
>