On Fri, Oct 6, 2017 at 2:38 AM, David Laight <david.lai...@aculab.com> wrote:
> From: William Tu
>> Sent: 05 October 2017 22:21
> ...
>> >> - if (skb->len > dev->mtu) {
>> >> + if (skb->len - dev->hard_header_len > dev->mtu) {
>> >
>> > Can you guarantee that skb->len > dev_hard_header_len?
>> > It is probably safer to check skb->len > dev->hard_header_len + dev->mtu
>> > since that addition isn't going to overflow.
>> Sure, I will fix it.
>>
>> >
>> >> pskb_trim(skb, dev->mtu);
>> >> truncate = true;
>> >
>> > Is that pskb_trim() now truncating to the correct size?
>>
>> You're right, now I should truncate to (dev->mtu + dev_hard_header_len)
>
> It might be worth caching that length in the dev structure
> to avoid the arithmetic on every packet.
>
> David
>
Thanks for the advise.
Yes, adding another field in the struct net_device can avoid the
arithmetic operation. I'm not sure it's a good idea to add new field
since there are already a lot in net_device. Let's wait to see how
others think.
William
