Re: reading the tcp headers within the write queue

Re: reading the tcp headers within the write queue

[David Miller]

From: Gavin McCullagh <Gavin.McCullagh@nuim.ie>
Date: Thu, 13 Dec 2007 18:56:26 +0000

> I'm trying to hack together something which will run through the
> retransmit queue looking at the tcp headers.

The packets in the retransmit queue are headerless, the
header only gets added to clones of the retransmit queue
frames during the actual transmit.

And this question belongs on netdev not linux-net.

Re: reading the tcp headers within the write queue

[Gavin McCullagh]

Hi,

thanks for the swift reply.

On Thu, 13 Dec 2007, David Miller wrote:

> > I'm trying to hack together something which will run through the
> > retransmit queue looking at the tcp headers.
> 
> The packets in the retransmit queue are headerless, the
> header only gets added to clones of the retransmit queue
> frames during the actual transmit.

Thought that might be it. I presume there isn't any other residue of the
tcp options elsewhere, that one could look at when the packet gets
acknowledged?  I'm particularly interested in the timestamp.

> And this question belongs on netdev not linux-net.

Oops, sorry.

Gavin

Re: reading the tcp headers within the write queue

[David Miller]

From: Gavin McCullagh <Gavin.McCullagh@nuim.ie>
Date: Thu, 13 Dec 2007 19:08:59 +0000

> Thought that might be it. I presume there isn't any other residue of the
> tcp options elsewhere, that one could look at when the packet gets
> acknowledged?  I'm particularly interested in the timestamp.

Every time we transmit, the timestamp will be different.

We store the jiffies at transmit time in TCP_SKB_CB(skb)->when,
so you can use that.  This is the value we use to compute the
timestamp.