linux-kernel - Re: [PATCH v13 02/12] livepatch: Helper macros to define livepatch structures

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Message-ID: <20181018111153.qcmvidttifi57u45@pathway.suse.cz>
Date:   Thu, 18 Oct 2018 13:11:53 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v13 02/12] livepatch: Helper macros to define livepatch
 structures

On Wed 2018-10-17 13:17:56, Josh Poimboeuf wrote:
> On Mon, Oct 15, 2018 at 02:37:03PM +0200, Petr Mladek wrote:
> > The definition of struct klp_func might be a bit confusing.
> > The original function is defined by name as a string.
> > The new function is defined by name as a function pointer
> > casted to unsigned long.
> > 
> > This patch adds helper macros that hide the different types.
> > The functions are defined just by the name. For example:
> 
> On one hand, these macros are kind of nice, because they do the function
> pointer casting for the user.
> 
> On the other hand, they hide the field names, which hurts readability a
> bit.  For example, it would be easy to accidentally assign the wrong
> callback function.

I am not a big fan of the macros either.


> Also, it's unfortunate that these macros are needed in the first place.
> 
> What if we just change new_addr (and old_addr) to be 'void *'?  Then the
> macros wouldn't be as useful, and we could just get rid of them.

Hmm, I wonder if any change make sense then. The above proposal might
just exchange one confusion with another one:

   + I would expect that a variable called addr is of the type
     unsigned long

   + we would need casting when calling ftrace API

   + .new_addr = function_xxx looks a bit weird and it will
     be used many times in all livepatch sources.


That said I could live with any solution. The livepatch code
is complicated from other reasons. This is only small detail
from my (today's ;-) point of view.

Best Regards,
Petr