Date: Tue, 30 Mar 2010 12:25:29 +0100 From: Rui Paulo <rpaulo@freebsd.org> To: jiani1012 <jiani1012@126.com> Cc: freebsd-net <freebsd-net@freebsd.org> Subject: Re: space of ath_node Message-ID: <06B53E1D-48A7-4739-9B94-CA6AC8AE902B@freebsd.org> In-Reply-To: <cba400.f3c8.127ac9383f3.Coremail.jiani1012@126.com>
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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
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