On Sat, 2015-02-28 at 19:22 +0300, Sergey P. Semernin wrote: > Hello All! > > I'm using Intel D2500 board with Atom processor as home router/media server. > It has Intel Gigabit Network adapter. This is lspci output: [...] > Some time ago, I bought the D-Link DGS-1100-08/A1A with VLAN support. Then, I > setup a tagged VLAN ports, one connected to the 82574L network adapter. > In the operation system I shared eth0 as eth0.1, eth0.2, and eth0.3 VLANs. > > Next time I saw receive errors on tagged port in the DGS-1100 admin interface. > My investigation resulted in conclusion that some small Ethernet packets with > VLAN tag has 64 bytes length. Minimum size for the Ethernet packet is 64 > byte, > and 4 byte is VLAN tag. So, smallest packet must be 68 bytes in my case. > > It seems that network adapter adds VLAN tag to the small frame, and then > append it to 64 bytes length. It's wrong.
It's right.
> I done simple patch to the e1000e module, and errors gone:
>
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c 2015-02-20
> 05:57:03.000000000 +0300
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c 2015-01-22
> 21:32:10.657649583 +0300
> @@ -5426,11 +5426,11 @@
> /* The minimum packet size with TCTL.PSP set is 17 bytes so
> * pad skb in order to meet this minimum size requirement
> */
> - if (unlikely(skb->len < 17)) {
> - if (skb_pad(skb, 17 - skb->len))
> + if (unlikely(skb->len < ETH_ZLEN)) {
> + if (skb_pad(skb, ETH_ZLEN - skb->len))
> return NETDEV_TX_OK;
> - skb->len = 17;
> - skb_set_tail_pointer(skb, 17);
> + skb->len = ETH_ZLEN;
> + skb_set_tail_pointer(skb, ETH_ZLEN);
> }
>
> mss = skb_shinfo(skb)->gso_size;
If the switch is stripping the VLAN tag from a minimum-length frame and
failing to add an extra 4 bytes of padding, that is a bug in the switch.
We will not patch e1000e or any other driver to work around that.
> If any additional information required, please contact me. I have some
> background in the Linux drivers development.
Maybe you should also read the Ethernet specs; they're free to download:
<http://standards.ieee.org/about/get/>. It is pretty clear that the
minimum frame length is not affected by the presence of a QTag
(VLAN/priority tag); only the maximum frame length is extended to allow
for the tag.
Ben.
--
Ben Hutchings
friends: People who know you well, but like you anyway.
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