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Date:	Fri, 1 Oct 2010 09:14:22 +1000
From:	Julian Calaby <>
To:	Johannes Berg <>
Subject: Re: [RFC 1/2] genetlink: introduce pre_doit/post_doit hooks

On Fri, Oct 1, 2010 at 08:55, Johannes Berg <> wrote:
> On Fri, 2010-10-01 at 08:51 +1000, Julian Calaby wrote:
>> > Come to think of it -- I could get away with a single pointer, since, if
>> > both are assigned,
>> >
>> > user_ptr[0] == wiphy_to_rdev(((netdev *)user_ptr[1])->ieee80211_ptr->wiphy)
>> >
>> > but that's a lot of pointy things, and some functions only have the rdev
>> > so it gets more complex. I think allowing two private pointers is a
>> > decent compromise.
>> Come to think of it -- if someone wanted to have a massive structure
>> with 10 pointers and a set of random data structures, then they could
>> easily create their priv struct and assign it to user_ptr[0], hence
>> rendering my argument null and void.
> Oh, well, I thought your argument was that it was arbitrary and not
> really necessary :-)

My argument was more that someone's likely to come up with a scheme
that requires more than 2 pointers, so why not accommodate them from
start with an element for a priv struct - but that requires a new
struct, allocating and freeing it, as well as heap space for it, and a
pointer on the stack to it. (though I'm sure there'll be some sensible
way to make them persistent, but that's another issue)

> Also, this rather cheap, it just needs a bit more stack space in a place
> that isn't typically deeply nested. So if some protocol came around and
> needed three pointers, I'd probably advocate just bumping it to three.
> At some point I might draw a line (10 is probably too much).

I was considering pointing out that a compromise might need to be
made, but I figured you'd already thought of that =)

> But you're right, of course, they can just use the first one and put
> something dynamically allocated into that, if really needed.




Julian Calaby

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