anchao commented on a change in pull request #1047:
URL: https://github.com/apache/incubator-nuttx/pull/1047#discussion_r425528457
##########
File path: net/netdev/netdev_register.c
##########
@@ -333,6 +335,18 @@ int netdev_register(FAR struct net_driver_s *dev, enum
net_lltype_e lltype)
return -EINVAL;
}
+ /* Update the package length */
+
+ if (dev->d_llhdrlen == 0)
+ {
+ dev->d_llhdrlen = llhdrlen;
+ }
+
+ if (dev->d_pktsize == 0)
+ {
+ dev->d_pktsize = pktsize;
+ }
+
Review comment:
Configure the MTU packet size in the SIM scenario is a invalid choice,
the MTU will only take effect at the link layer when configuring the tunnel
bridge:
tools/simbridge.sh:
```
if [ "$2" == "on" ]; then
ip link add nuttx0 type bridge
ip addr flush dev $1
+ ip link set dev nuttx0 mtu size?
ip link set $1 master nuttx0
ip link set dev nuttx0 up
dhclient nuttx0
```
```
nuttx0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.2.15 netmask 255.255.255.0 broadcast 10.0.2.255
inet6 fe80::a00:27ff:fe63:d2e7 prefixlen 64 scopeid 0x20<link>
```
If the nuttx MTU size is small than tunnel, the larger packets will do drop
processing at:
net/devif/ipv4_input.c:
...
377 /* Check the size of the packet. If the size reported to us in d_len
is
378 * smaller the size reported in the IP header, we assume that the
packet
379 * has been corrupted in transit. If the size of d_len is larger than
the
380 * size reported in the IP packet header, the packet has been padded
and
381 * we set d_len to the correct value.
382 */
383
384 totlen = (ipv4->len[0] << 8) + ipv4->len[1];
385 if (totlen <= dev->d_len)
386 {
387 dev->d_len = totlen;
388 }
389 else
390 {
391 nwarn("WARNING: IP packet shorter than length in IP header\n");
392 goto drop;
393 }
...
in this situation, I think obtain the MTU size dynamically is a necessary
choice.
Regarding your concerns, We will check further whether there is side effects
in the mainline.
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