anchao commented on code in PR #7616:
URL: https://github.com/apache/incubator-nuttx/pull/7616#discussion_r1027227824
##########
net/devif/devif_poll.c:
##########
@@ -616,12 +616,71 @@ static inline int devif_poll_tcp_connections(FAR struct
net_driver_s *dev,
# define devif_poll_tcp_connections(dev, callback) (0)
#endif
+/****************************************************************************
+ * Name: devif_poll_callback
+ *
+ * Description:
+ * This function will help us to gather multiple iob memory slices into a
+ * linear device buffer. if devices with small memory, this function will
+ * trigger a memory copy if net device start transmit the iob slices to
+ * flat buffer
+ *
+ ****************************************************************************/
+
+static int devif_poll_callback(FAR struct net_driver_s *dev)
+{
+ FAR struct iob_s *iob;
+ uint16_t llhdrlen;
+ int bstop = false;
+
+ if (dev->d_len > 0 && dev->d_iob != NULL)
+ {
+ llhdrlen = NET_LL_HDRLEN(dev);
+
+ /* Copy iob to flat buffer */
+
+ iob_copyout(dev->d_pollbuf + llhdrlen, dev->d_iob, dev->d_len, 0);
+
+ /* Copy l2 header (arp out) */
+
+ memcpy(dev->d_pollbuf,
+ dev->d_iob->io_data + (CONFIG_NET_LL_GRUARDSIZE - llhdrlen),
+ llhdrlen);
+
+ /* Save iob buffer and restore flat buffer pointer */
+
+ iob = dev->d_iob;
+ dev->d_iob = NULL;
+ dev->d_buf = dev->d_pollbuf;
+
+ /* Call the real device callback */
+
+ bstop = dev->d_pollcallback(dev);
+ if (bstop)
+ {
+ /* Polling stop, release iob buffer */
+
+ iob_free_chain(iob);
+ dev->d_buf = NULL;
+ }
+ else
+ {
+ /* Continue polling, restore iob */
+
+ dev->d_iob = iob;
+ dev->d_buf = (FAR void *)ETHBUF;
Review Comment:
Yes, ETHBUF will be cast to (struct eth_hdr_s), and the type of d_buf is
(uint8_t *)
```
FAR uint8_t *d_buf;
#define ETHBUF ((FAR struct eth_hdr_s *) \
(dev->d_iob ? \
&dev->d_iob->io_data[CONFIG_NET_LL_GRUARDSIZE -
NET_LL_HDRLEN(dev)] : \
dev->d_buf))
```
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