Re: RE : a simple list

[vincent guffens <v.guffens@imperial.ac.uk>]

Thank you for this information. Adding the concept of context is indeed
the right idea. I was doing it as follows

void function (grub_device_t dev)
{
 grub_device_t it;
 auto int look_for_dev (grub_device_t);

  int look_for_dev (grub_device_t grub_device_t other_dev)
  {
     return compare (dev, other_dev)
  }

grub_iterate_list_brk (grub_devices, look_for_dev, it);
}

but it has to be compared with something like

void function (grub_device_t dev)
{
  grub_device_t it = grub_devices;

  while (it)
  {
     if ( compare (dev, it) )
       break;
  }
}


which is obviously simpler. Maybe the only two functions that are really
needed are add and del ?

Also, I found out yesterday that
the compiler throws out warning about strict aliasing when using the
iterate function. I had to add -fno-strict-aliasing to get rid of them.



Eric Salomé wrote:
> Hi,
> 
> I didn’t take a good look at current iterate functions in Grub 2, yet.
> 
>  
> 
> Most iterations needs a “init” (before treatment of first item) and a
> “fini” (after treatment of last item).
> 
> Further more, one might want to make iteration functions “re-entrant”
> (or recursive), or call-back other functions in a generic way.
> 
>  
> 
> One way to get to such behavior easily cost a bit more than the example
> you provided : 
> 
> you may just add an argument (let’s call it the context object) to the
> call of the iterate function :
> 
>  
> 
> #define grub_iterate_list(list, func, context) \
>   {typeof(list) el = list; while (el) {func(context, el); el=el->next;}
> func(context, NULL)}
> or
> 
> #define grub_iterate_list(list, func) \
>   {void * context = NULL; typeof(list) el = list; while (el)
> {func(&context, el); el=el->next;} func(&context, NULL)}
> but I prefer the first define as it allows transmission of a full
> context to the iteration function.
> 
>  
> 
> my_struct * my_ctxt;
> 
>  
> 
> my_ctxt = NULL; grub_iterate_list(list, my_func, &my_ctxt);
> 
>  
> 
> void my_func (my_struct ** ctxt, my_item * item) {
> 
>       if (item == NULL) {
> 
>           /* End of iteration : Do any cleanup */
> 
>           if (*ctxt == NULL) return;
> 
>           free (*ctxt) ……
> 
>           …..
> 
>           return;
> 
>       }
> 
>       if (*ctxt == NULL) {
> 
>            /* First iteration : Do any initialization */
> 
>            *ctxt = malloc (sizeof (my_struct)); ….
> 
>            …..
> 
> }
> 
> /* Do the iteration stuff */
> 
> …..
> 
> return;
> 
> }
> 
>  
> 
> In grub_iterate_list_brk, you can use context to send a patern or model
> object to compare each item of the list with.
> 
>  
> 
> The draw back is it makes iteration function a bit less readable, but a
> lot more powerful.
> 
>                         
> 
> _________________________________________
> 
> Eric Salomé – Paris, France
> 
>  
> 
> -----Message d'origine-----
> De : grub-devel-bounces+esalome=ctx.net@gnu.org
> [mailto:grub-devel-bounces+esalome=ctx.net@gnu.org] De la part de
> Guffens, Vincent
> Envoyé : lundi 8 mai 2006 01:14
> À : grub-devel@gnu.org
> Objet : a simple list
> 
>  
> 
> Hi,
> 
> I need to use a simple list to register the pci devices, drivers and so
> on. I notice that there are lists like that already in the code so what
> would you think about having a list.h file like that ?
> 
> /* A very simple list.
>  *
>  * If you want a list of struct myitem
>  * you do
>  *
>  * struct myitem *item_list;
>  *
>  * where myitem MUST have its next pointer as the FIRST field
>  *
>  * and you can then add, delete the EL item,
>  * grub_add_list (&item_list, el);
>  * grub_del_list (&item_list, el);
>  *
>  * or call HOOK(item) for each element of the list
>  * grub_iterate_list (item_list, hook);
>  *
>  * This brk version will point el to the list item for which
>  * HOOK(EL) returns a non-null value
>  * grub_iterate_list_brk (item_list, hook, el);
>  *
>  */
> 
> struct obj {
>   struct obj *next; /* MUST BE FIRST */
> };
> 
> #define grub_del_list(list, el) _grub_del_list((struct obj**) list,
> (struct obj*) el)
> #define grub_add_list(list, el) _grub_add_list((struct obj**) list,
> (struct obj*) el)
> #define grub_find_list(list, el) \
>   (typeof(list)) _grub_find_list((struct obj*) list, (struct obj*) el)
> #define grub_iterate_list(list, func) \
>   {typeof(list) el = list; while (el) {func(el); el=el->next;}}
> #define grub_iterate_list_brk(list, func, it) \
>   {typeof(list) el = list; it = 0; \
>     while (el) {if (func(el)) {it = el; break;} el=el->next; }}
> 
> static inline struct obj*  _grub_find_list (struct obj *list, struct obj
> *el)
> {
>   struct obj *it = list;
>   for (it = list; it; it=it->next)
>   {
>     if (it == el) return el;
>   }
>   return 0;
> };
> 
> static inline void _grub_add_list (struct obj **list, struct obj *el)
> {
>   if ( (!el) || (_grub_find_list (*list, el)) )
>     return;
>  
>   el->next = *list;
>   *list = el;
> };
> 
> static inline void _grub_del_list (struct obj **list, struct obj *el)
> {
>   struct obj **p;
>   struct obj *q;
> 
>   for (p = list, q = *p; q; p = &(q->next), q = q->next)
>     if (q == el)
>       {
>         *p = q->next;
>         break;
>       }
> };
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
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-- 
		Vincent Guffens
		Intelligent Systems & Networks Group
		Research associate, Imperial College