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

Josh Poimboeuf
2018-10-18T12:58:35Z

On Thu, Oct 18, 2018 at 01:11:53PM +0200, Petr Mladek wrote:
> 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.

Fair points. Instead of changing new_func to new_addr, how about we
leave it alone, and instead change 'unsigned long old_addr' to 'void
*old_func'?

That would give us consistent naming internally, while making the
external interface more sensible and cast-free.

We'd still have to cast when passing to the ftrace API, but IMO it would
be worth it.

--
Josh