Hi,
On Sat, 2 Dec 2006, Al Viro wrote:
> > > > You need some more magic macros to access/modify the data field.
> > >
> > > Which is done bloody rarely. grep and you'll see... BTW, there are
> > > other reasons why passing struct timer_list * is wrong:
> > > * direct calls of the timer callback
> >
> > Why should that be wrong?
>
> Need to arrange a struct timer_list?
How is that different from arranging some struct foo? Either you need a
reference object anyway or a NULL pointer works in both cases.
> > > * see a timer callback, decide it looks better as a tasklet.
> > > What, need a different glue now?
> >
> > What's wrong with changing the prototype? If you don't do it, the compiler
> > will complain about it anyway.
>
> How about "not having to change it at all"?
If it were a common operation, this might have some value...
> > > Look, it's a delayed call. The less glue we need, the better - the
> > > rules are much simpler that way, so that alone means that we'll get
> > > fewer fsckups.
> >
> > You have the glue in a different place, so what?
>
> Where?
In SETUP_TIMER.
> > The other alternative has real _practical_ value in almost every case,
> > which I very much prefer. What's wrong with that?
>
> Lack of any type safety whatsoever, magic boilerplates in callback instances,
> rules more complex than "your callback should take a pointer, don't cast
> anything, it's just a way to arrange for a delayed call, nothing magical
> needed"?
I admit the compile check in SETUP_TIMER() is clever, but this way all the
magic is in this place and is it really worth it? You're only adding _one_
extra typecheck for mostly simple cases anyway.
The container_of() method is not new and is already well used in other
places, it has real practical advantages, which would make the change
actually worthwile.
bye, Roman
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