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

Jiri Olsa
2022-01-14T15:18:35Z

On Thu, Jan 13, 2022 at 10:15:32PM +0900, Masami Hiramatsu wrote:
> On Thu, 13 Jan 2022 13:25:52 +0100
> Jiri Olsa <jolsa@redhat.com> 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 <mhiramat@kernel.org>
>