On Sat, Oct 9, 2010 at 6:16 PM, Bond <jamesbond.2k.g@xxxxxxxxx> wrote:
But the same task can be done at compile time by using the maco LIST_HEAD_INIT()I read that link but could not understand much out of it.On Sat, Oct 9, 2010 at 12:27 PM, Manish Katiyar <mkatiyar@xxxxxxxxx> wrote:
> On Fri, Oct 8, 2010 at 11:38 PM, Bond <jamesbond.2k.g@xxxxxxxxx> wrote:
>> Hi,in
>> http://lxr.linux.no/#linux+v2.6.18/include/linux/list.h
>> following section of code
>> there is a structure which is defined as
>>
>> struct list_head {
>> struct list_head *next, *prev;
>> };
>>
>> It is used in another file as
>>
>> #define LIST_HEAD_INIT(name) { &(name), &(name) }
>>
>> #define LIST_HEAD(name) \
>> struct list_head name = LIST_HEAD_INIT(name)
>>
>> static inline void INIT_LIST_HEAD(struct list_head *list)
>> {
>> list->next = list;
>> list->prev = list;
>> }
>>
>>
>> I came across a book where the code is given as follows in an example
>>
>> include/linux/list.h
>> struct list_head {
>> struct list_head *next,*prev;
>> };
>> #define LIST_HEAD_INIT(name) {&(name),&(name)}
>>
>> #define LIST_HEAD(name) struct list_head name = LIST_HEAD_INIT(name)
>> #define INIT_LIST_HEAD(prt) do {\
>> (ptr)->next = (ptr);(ptr)->prev= (ptr);\
>> }while(0)
>>
>>
>> I was not able to understand above code segment.
>> I am aware of what a #define is but still I could not understand above thing.
>> Can some one help in understanding with some example.
>> Not related to Linux Kernel a normal example where I
>> can make a link list with above defined way.
>
> 0
>
>>
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The list_head structure here is used inside your structure which's used as the nodes for linked list .
Whenever you are going to create a node for your list , all the pointers next and prev are initialized to point to itself.This is what INIT_LIST_HEAD
does
.
In fact both of them are used for the same task .
Now We need a starting point for the list . This variable points to the first element of the list. We use the variable of type list_head to accomplish this . this is often used as a local variable so that you can do it anywhere in your kernel .
So to initialize this we use the macro LIST_HEAD()
we add elements to this list using the list_add function( api you could call it)
