Hi all,
Is there a reason the structures that need a forced alignment in lwip
aren't declared something like this:
take pbuf.c for example:
typedef unsigned long LWIP_ALIGN_TYPE;
struct pool_pbuf
{
struct pbuf pbuf; // "inherit" a pbuf. C guaranties the first member
takes the same address of the container. pool_pbuf b; &b == &b.pbuf
-> (struct pbuf* )&b is ok.
union
{
LWIP_ALIGN_TYPE force_align;
u8_t payload_buf[MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE)];
};
};
static struct pool_pbuf mem[PBUF_POOL_SIZE];
Then in pbuf_init:
void
pbuf_init(void)
{
u16_t i;
pbuf_pool = (struct pbuf* )mem; // already aligned
#if PBUF_STATS
lwip_stats.pbuf.avail = PBUF_POOL_SIZE;
#endif /* PBUF_STATS */
/* Set up ->next pointers to link the pbufs of the pool together */
for(i = 0; i < PBUF_POOL_SIZE; ++i) {
p = (struct pbuf* )mem[i];
p->next = (struct pbuf*)mem[i+1];
p->len = p->tot_len = MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE);
p->payload = mem[i].payload_buf;
p->flags = PBUF_FLAG_POOL;
}
/* The ->next pointer of last pbuf is NULL to indicate that there
are no more pbufs in the pool */
mem[PBUF_POOL_SIZE-1]->next = NULL;
#if !SYS_LIGHTWEIGHT_PROT
pbuf_pool_alloc_lock = 0;
pbuf_pool_free_lock = 0;
pbuf_pool_free_sem = sys_sem_new(1);
#endif
}
and where an offset if requested:
p->payload = MEM_ALIGN(p->payload_buf + offset);
If there are compilers that don't support anonymouse unions we can have
simple macros and named unions.
I never tested this, but I am sure that this would shave a few ram bytes
in many arquitectures. Right now we allocate more than needed.
For example:
u8_t mem[MEM_ALIGNMENT - 1 + PBUF_POOL_SIZE *
MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE + sizeof(struct pbuf))];
allocates MEM_ALIGNMENT - 1 bytes too much if mem ends up already aligned.
What do you think?
Cheers,
Pedro Alves
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