net: ip: net_pkt: only reserve L2 header for TX case

Only reserve L2 header for TX case when allocating net buffer,
as for RX case, all the received headers are already in linear
buffer when the driver receives the data, and reserve extra L2
header for RX case may exceed the default buffer size.

Signed-off-by: Maochen Wang <[email protected]>

Author: MaochenWang1

subsys/net/ip/net_pkt.c

@@ -1337,6 +1337,16 @@ int net_pkt_alloc_buffer_with_reserve(struct net_pkt *pkt,
 	return 0;
 }
 
+static bool is_pkt_tx(struct net_pkt *pkt)
+{
+#if defined(CONFIG_NET_CONTEXT_NET_PKT_POOL)
+	if ((pkt->context != NULL) && (get_tx_slab(pkt->context) != NULL)) {
+		return pkt->slab == get_tx_slab(pkt->context);
+	}
+#endif
+	return pkt->slab == &tx_pkts;
+}
+
 #if NET_LOG_LEVEL >= LOG_LEVEL_DBG
 int net_pkt_alloc_buffer_debug(struct net_pkt *pkt,
 			       size_t size,
@@ -1364,7 +1374,7 @@ int net_pkt_alloc_buffer(struct net_pkt *pkt,
 
 	iface = net_pkt_iface(pkt);
 
-	if (iface != NULL && net_if_l2(iface)->alloc != NULL) {
+	if (iface != NULL && is_pkt_tx(pkt) && net_if_l2(iface)->alloc != NULL) {
 		ret = net_if_l2(iface)->alloc(iface, pkt, size, proto, timeout);
 		if (ret != -ENOTSUP) {
 			return ret;