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Clarify LWIP_NETIF_TX_SINGLE_PBUF (drivers might still get chained pbufs and have to take care of that, e.g. by using pbuf_alloc_copy)

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This commit is contained in:
goldsimon 2017-04-25 10:09:32 +02:00
parent dcb2cb99a1
commit 4b68605276
1 changed files with 11 additions and 2 deletions
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13
src/include/lwip/opt.h
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@ -1514,13 +1514,22 @@
#endif
/**
* LWIP_NETIF_TX_SINGLE_PBUF: if this is set to 1, lwIP tries to put all data
* LWIP_NETIF_TX_SINGLE_PBUF: if this is set to 1, lwIP *tries* to put all data
* to be sent into one single pbuf. This is for compatibility with DMA-enabled
* MACs that do not support scatter-gather.
* Beware that this might involve CPU-memcpy before transmitting that would not
* be needed without this flag! Use this only if you need to!
*
* @todo: TCP and IP-frag do not work with this, yet:
* ATTENTION: a driver should *NOT* rely on getting single pbufs but check TX
* pbufs for being in one piece. If not, @ref pbuf_alloc_copy can be used to get
* a single pbuf:
* if (p->next != NULL) {
* struct pbuf *q = pbuf_alloc_copy(PBUF_RAW, PBUF_RAM, p);
* if (q == NULL) {
* return ERR_MEM;
* }
* p = q; ATTENTION: do NOT free the old 'p' as the ref belongs to the caller!
* }
*/
#if !defined LWIP_NETIF_TX_SINGLE_PBUF || defined __DOXYGEN__
#define LWIP_NETIF_TX_SINGLE_PBUF 0