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arp/ndp: allow overriding the decision to copy pbufs

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lwIP aims to support zero-copy TX, and thus, must internally handle
all cases that pbufs are referenced rather than copied upon low-level
output.  However, in the current situation, the arp/ndp packet queuing
routines conservatively copy entire packets, even when unnecessary in
cases where lwIP is used in a zero-copy compliant manner.  This patch
moves the decision whether to copy into a centralized macro, allowing
zero-copy compliant applications to override the macro to avoid the
unnecessary copies.  The macro defaults to the safe behavior, though.
This commit is contained in:
David van Moolenbroek 2017-02-27 14:43:58 +00:00 committed by goldsimon
parent 27c835aa56
commit d3fc398580
3 changed files with 22 additions and 8 deletions
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7
src/core/ipv4/etharp.c
View File

@ -996,13 +996,12 @@ etharp_query(struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
/* entry is still pending, queue the given packet 'q' */
struct pbuf *p;
int copy_needed = 0;
/* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
* to copy the whole queue into a new PBUF_RAM (see bug #11400)
* PBUF_ROMs can be left as they are, since ROM must not get changed. */
/* IF q includes a pbuf that must be copied, copy the whole chain into a
* new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
p = q;
while (p) {
LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));
if (p->type != PBUF_ROM) {
if (PBUF_NEEDS_COPY(p)) {
copy_needed = 1;
break;
}

7
src/core/ipv6/nd6.c
View File

@ -2034,12 +2034,11 @@ nd6_queue_packet(s8_t neighbor_index, struct pbuf *q)
return ERR_ARG;
}
/* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
* to copy the whole queue into a new PBUF_RAM (see bug #11400)
* PBUF_ROMs can be left as they are, since ROM must not get changed. */
/* IF q includes a pbuf that must be copied, we have to copy the whole chain
* into a new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
p = q;
while (p) {
if (p->type != PBUF_ROM) {
if (PBUF_NEEDS_COPY(p)) {
copy_needed = 1;
break;
}

16
src/include/lwip/pbuf.h
View File

@ -55,6 +55,22 @@ extern "C" {
#define LWIP_SUPPORT_CUSTOM_PBUF ((IP_FRAG && !LWIP_NETIF_TX_SINGLE_PBUF) || (LWIP_IPV6 && LWIP_IPV6_FRAG))
#endif
/** PBUF_NEEDS_COPY(p): return a boolean value indicating whether the given
* pbuf needs to be copied in order to be kept around beyond the current call
* stack without risking being corrupted. The default setting provides safety:
* it will make a copy iof any pbuf chain that does not consist entirely of
* PBUF_ROM type pbufs. For setups with zero-copy support, it may be redefined
* to evaluate to true in all cases, for example. However, doing so also has an
* effect on the application side: any buffers that are *not* copied must also
* *not* be reused by the application after passing them to lwIP. For example,
* when setting PBUF_NEEDS_COPY to (0), after using udp_send() with a PBUF_RAM
* pbuf, the application must free the pbuf immediately, rather than reusing it
* for other purposes. For more background information on this, see tasks #6735
* and #7896, and bugs #11400 and #49914. */
#ifndef PBUF_NEEDS_COPY
#define PBUF_NEEDS_COPY(p) ((p)->type != PBUF_ROM)
#endif /* PBUF_NEEDS_COPY */
/* @todo: We need a mechanism to prevent wasting memory in every pbuf
(TCP vs. UDP, IPv4 vs. IPv6: UDP/IPv4 packets may waste up to 28 bytes) */