netdev - Re: [PATCH] net-timestamp: Fix a documentation typo

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Date:	Mon, 24 Nov 2014 17:11:28 -0500
From:	Willem de Bruijn <willemb@...gle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] net-timestamp: Fix a documentation typo

On Mon, Nov 24, 2014 at 3:02 PM, Andy Lutomirski <luto@...capital.net> wrote:
> SOF_TIMESTAMPING_OPT_ID puts the id in ee_data, not ee_info.
>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Andy Lutomirski <luto@...capital.net>

Acked-by: Willem de Bruijn <willemb@...gle.com>

> ---

Thanks for sending a fix.

> While I'm here, the docs say:
>
>     In practice, it [ee_data] is a monotonically increasing u32 (that wraps).
>
> Is user code supposed to rely on this and, further, on the fact that the
> counter starts at zero?  If not, how else is user code supposed to match
> outgoing data to timestamps?

That is correct. The per-socket counter is reset when
SOF_TIMESTAMPING_OPT_ID is set. On datagram sockets, it returns the
packet number since the reset. On stream sockets, it returns the byte
offset since the reset.

> Also, is it intentional that the payload data associated with the tx
> timestamp is (I think) the full outgoing packet including lower-layer
> headers?

Absolutely not. I'll look into that right away. It doesn't on ACK, and
should certainly not expose this info in the other cases, either.

> And, finally, would it be possible to attach IP_PKTINFO to the looped
> timestamp?  That way I could finally update my fancy ping program to
> track which outgoing interface was used for a request.

If socket option IP_PKTINFO is set, you want to receive in_pktinfo for
any packet that happens to be queued onto the error queue? Both
SKB_EXT_ERR(skb) and PKTINFO_SKB_CB(skb) use the control block to
store data that is later encoded in a cmsg, so there may not be enough
room to hold both. I'll take a look.
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