Re: Misalignment, MIPS, and ip_hdr(skb)->version

From: David Miller
Date: Thu Dec 08 2016 - 18:15:05 EST

From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Date: Thu, 8 Dec 2016 23:20:04 +0100

> Hi David,
> On Thu, Dec 8, 2016 at 1:37 AM, David Miller <davem@xxxxxxxxxxxxx> wrote:
>> You really have to land the IP header on a proper 4 byte boundary.
>> I would suggest pushing 3 dummy garbage bytes of padding at the front
>> or the end of your header.
> Are you sure 3 bytes to get 4 byte alignment is really the best? I was
> thinking that adding 1 byte to get 2 byte alignment might be better,
> since it would then ensure that the subsequent TCP header winds up
> being 4 byte aligned. Or is this in fact not the desired trade off,
> and so I should stick with the 3 bytes you suggested?

If the IP header is 4 byte aligned, the TCP header will be as well.