Re: [ckrm-tech] [RFC][PATCH] UBC: user resource beancounters

[Chandra Seetharaman <sekharan@us.ibm.com>]

On Thu, 2006-08-24 at 19:55 -0400, Kyle Moffett wrote:
> On Aug 24, 2006, at 19:48:28, Chandra Seetharaman wrote:
> > On Thu, 2006-08-24 at 12:10 +0100, Alan Cox wrote:
> >> All you need is
> >>
> >> struct wombat_controller
> >> {
> >> 	struct user_beancounter counter;
> >> 	void (*wombat_pest_control)(struct wombat *w);
> >> 	atomic_t wombat_population;
> >> 	int (*wombat_destructor)(struct wombat *w);
> >> };
> >
> > This may not solve the problem, as
> >  - we won't be able get the controller data structure given the  
> > beancounter data structure.
> 
> Of course you can!  This is what we do for linked lists too.  Here's  
> an example of how to get a pointer to your wombat_controller given  
> the user_beancounter pointer:
> struct wombat_controller *wombat = containerof 
> (ptr_to_user_beancounter, struct wombat_controller, counter);
> 
> The containerof(PTR, TYPE, MEMBER) returns a pointer to the parent  
> object of type "TYPE" whose member "MEMBER" has address "PTR".

Yes, it would work nicely. 

But, the problem is that the struct user_beancounter (part of
wombat_controller above) is a _copy_ of the original, not the original
itself. We cannot keep the original (in _each_ controller), as there may
be more than one controller in the system and user_beancounter structure
is created/owned/destroyed by the beancounter infrastructure and not the
controller.

> Cheers,
> Kyle Moffett
> 
> 
> 
> 
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    Chandra Seetharaman               | Be careful what you choose....
              - sekharan@us.ibm.com   |      .......you may get it.
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