linux-kernel - Re: [POC 0/7] livepatch: Make livepatch states, callbacks, and shadow variables work together

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Message-ID: <20231110213317.g4wz3j3flj7u2qg2@treble>
Date:   Fri, 10 Nov 2023 13:33:17 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [POC 0/7] livepatch: Make livepatch states, callbacks, and
 shadow variables work together

On Fri, Nov 10, 2023 at 06:04:21PM +0100, Petr Mladek wrote:
> This POC is a material for the discussion "Simplify Livepatch Callbacks,
> Shadow Variables, and States handling" at LPC 2013, see
> https://lpc.events/event/17/contributions/1541/
> 
> It obsoletes the patchset adding the garbage collection of shadow
> variables. This new solution is based on ideas from Nicolai Stange.
> And it should also be in sync with Josh's ideas mentioned into
> the thread about the garbage collection, see
> https://lore.kernel.org/r/20230204235910.4j4ame5ntqogqi7m@treble

Nice!  I like how it brings the "features" together and makes them easy
to use.  This looks like a vast improvement.

Was there a reason to change the naming?  I'm thinking

  setup / enable / disable / release

is less precise than

  pre_patch / post_patch / pre_unpatch / post_unpatch.

Also, I'm thinking "replaced" instead of "obsolete" would be more
consistent with the existing terminology.

For example, in __klp_enable_patch():

	ret = klp_setup_states(patch);
	if (ret)
		goto err;

	if (patch->replace)
		klp_disable_obsolete_states(patch);

it's not immediately clear why "disable obsolete" would be the "replace"
counterpart to "setup".

Similarly, in klp_complete_transition():

	if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) {
		klp_unpatch_replaced_patches(klp_transition_patch);
		klp_discard_nops(klp_transition_patch);
		klp_release_obsolete_states(klp_transition_patch);
	}

it's a little jarring to have "unpatch replaced" followed by "release
obsolete".

So instead of:

  int  klp_setup_states(struct klp_patch *patch);
  void klp_enable_states(struct klp_patch *patch);
  void klp_disable_states(struct klp_patch *patch);
  void klp_release_states(struct klp_patch *patch);

  void klp_enable_obsolete_states(struct klp_patch *patch);
  void klp_disable_obsolete_states(struct klp_patch *patch);
  void klp_release_obsolete_states(struct klp_patch *patch);

how about something like:

  int  klp_states_pre_patch(void);
  void klp_states_post_patch(void);
  void klp_states_pre_unpatch(void);
  void klp_states_post_unpatch(void);

  void klp_states_post_patch_replaced(void);
  void klp_states_pre_unpatch_replaced(void);
  void klp_states_post_unpatch_replaced(void);

?

(note that passing klp_transition_patch might be optional since state.c
already has visibility to it anyway)

-- 
Josh