space of ath_node

[Rui Paulo]

On 30 Mar 2010, at 01:58, jiani1012 wrote:

> Hi,all    
>        A problem puzzled me in ath code. The following code in function  ath_node_alloc( ) shows the space allocated to an,
> 
>> struct ath_ratectrl {
>> size_t arc_space;    /* space required for per-node state */
>> }; 
> 
>> const size_t space = sizeof(struct ath_node) + sc->sc_rc->arc_space;
>> struct ath_node *an;
>> an = malloc(space, M_80211_NODE, M_NOWAIT|M_ZERO);
> 
> but in the two lines below ,what is (an)[1]?  Where is the initialization of (an)[1]? What does it contain? Can you show me? and how to get the content of sn?
> 
>> struct sample_node *sn = ATH_NODE_SAMPLE(an);       /*in sample.c*/
>> #define ATH_NODE_SAMPLE(an) ((struct sample_node *)&(an)[1])      /*in sample.h*/
> 
> Otherwise, the struct ath_ratectrl has been used in structures ath_softc, sample_softc and so on. Is there any relations between them?

Think about memory in the following way:

an[0] .................................. an[1] ...................
      struct ath_node                          struct sample_node 

Indexing an[1] gives the address past the end of struct ath_node, which is the start address of struct sample_node.

--
Rui Paulo