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Re: [RFC] timers, pointers to functions and type safety

From:  Ingo Molnar <>
To:  Al Viro <>
Subject:  Re: [RFC] timers, pointers to functions and type safety
Date:  Mon, 4 Dec 2006 12:48:51 +0100
Cc:  Thomas Gleixner <>, Matthew Wilcox <>, Linus Torvalds <>,,
Archive-link:  Article, Thread

* Al Viro <> wrote:

> > This is going to make a lot of data structures smaller, when the 
> > timer_list is embedded in the structure itself and for the lot, 
> > which ignores the timer callback argument anyway.
> container_of => still lousy type safety.  All over the sodding place.

the question is: which is more important, the type safety of a 
container_of() [or type cast], which if we get it wrong produces a 
/very/ trivial crash that is trivial to fix - or embedded timers data 
structure size all around the kernel? I believe the latter is more 

and we could have a runtime debugging option to tie the type of the 
structure to the timer list entry. For example by using 
__builtin_classify_type(), sizeof() and offsetof() to fingerprint timer 
structs at init_timer time, and then checking for that at container_of() 
time - or something like that. In fact, gcc should really give us a 
better way to categorize types than __builtin_classify_type(). We could 
probably improve the situation by having some global registry of types 
known to the kernel, via a huge switch() around 


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