RE : a simple list

["Eric Salomé" <esalome@ctx.net>]

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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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