netdev - Re: [PATCH net-next 1/2] tcp: Extend SOF_TIMESTAMPING_RX

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Date:   Tue, 22 Aug 2017 14:57:32 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Mike Maloney <maloneykernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Mike Maloney <maloney@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: Extend SOF_TIMESTAMPING_RX_SOFTWARE to
 TCP recvmsg

On Tue, Aug 22, 2017 at 1:27 PM, Mike Maloney <maloneykernel@...il.com> wrote:
> From: Mike Maloney <maloney@...gle.com>
>
> When SOF_TIMESTAMPING_RX_SOFTWARE is enabled for tcp sockets, return the
> timestamp corresponding to the highest sequence number data returned.
>
> Previously the skb->tstamp is overwritten when a TCP packet is placed
> in the out of order queue.  While the packet is in the ooo queue, save the
> timestamp in the TCB_SKB_CB.  This space is shared with the gso_*
> options which are only used on the tx path, and a previously unused 4
> byte hole.
>
> When skbs are coalesced either in the sk_receive_queue or the
> out_of_order_queue always choose the timestamp of the appended skb to
> maintain the invariant of returning the timestamp of the last byte in
> the recvmsg buffer.
>

> +static void tcp_update_recv_tstamps(struct sk_buff *skb,
> +                                   struct scm_timestamping *tss)
> +{
> +       if (skb->tstamp)
> +               tss->ts[0] = ktime_to_timespec(skb->tstamp);
> +       else
> +               tss->ts[0] = (struct timespec) {0};
> +
> +       if (skb_hwtstamps(skb)->hwtstamp)
> +               tss->ts[2] = ktime_to_timespec(skb_hwtstamps(skb)->hwtstamp);
> +       else
> +               tss->ts[2] = (struct timespec) {0};

tss->ts[1] may remain uninitialized.