linux-kernel - Re: [PATCH 2/2] livepatch: introduce patch/func-walking helpers

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Date:	Wed, 20 May 2015 09:51:43 +0800
From:	Minfei Huang <mnfhuang@...il.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Jiri Slaby <jslaby@...e.cz>, live-patching@...r.kernel.org,
	jpoimboe@...hat.com, sjenning@...hat.com, vojtech@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] livepatch: introduce patch/func-walking helpers

On 05/19/15 at 11:58P, Jiri Kosina wrote:
> On Tue, 19 May 2015, Minfei Huang wrote:
> 
> > > klp_for_each_object and klp_for_each_func are now used all over the
> > > code. One need not think what is the proper condition to check in the
> > > for loop now.
> > > 
> > > Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> > > ---
> > >  include/linux/livepatch.h |  6 ++++++
> > >  kernel/livepatch/core.c   | 18 +++++++++---------
> > >  2 files changed, 15 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> > > index fe45f2f02c8d..31db7a05dd36 100644
> > > --- a/include/linux/livepatch.h
> > > +++ b/include/linux/livepatch.h
> > > @@ -805,7 +805,7 @@ static int klp_init_patch(struct klp_patch *patch)
> > >  	if (ret)
> > >  		goto unlock;
> > >  
> > > -	for (obj = patch->objs; obj->funcs; obj++) {
> > > +	klp_for_each_object(patch, obj) {
> > >  		ret = klp_init_object(patch, obj);
> > >  		if (ret)
> > >  			goto free;
> > > @@ -960,7 +960,7 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
> > >  		mod->klp_alive = false;
> > >  
> > >  	list_for_each_entry(patch, &klp_patches, list) {
> > > -		for (obj = patch->objs; obj->funcs; obj++) {
> > > +		klp_for_each_object(patch, obj) {
> > 
> > The code is more clearly to use "if", instead of the loop, although we will take
> > more than one line than previous, since we will always get the first function
> > from the object.
> 
> I have absolutely no idea what you are trying to say here, sorry. Could 
> you please try to rephrase your review comment?
> 

Sure. Sorry for confuse you with my comment.

Following is the livepatch code.

list_for_each_entry(patch, &klp_patches, list) {
	for (obj = patch->objs; obj->funcs; obj++) {
----------------------------------
We get the fisrt object from the patch, then we break the loop. The code is more clearly to
use "if", instead of the loop.
----------------------------------
		if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
			continue;

		if (action == MODULE_STATE_COMING) {
			obj->mod = mod;
			klp_module_notify_coming(patch, obj);
		} else /* MODULE_STATE_GOING */
			klp_module_notify_going(patch, obj);

		break;
----------------------------------
Here we break the loop.
----------------------------------
	}
}

Thanks
Minfei
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