On Thu, Apr 27, 2017 at 12:21:00PM -0400, Willem de Bruijn wrote:
> >> > @@ -720,6 +720,7 @@ void __sock_recv_timestamp(struct msghdr *msg,
> >> > struct sock *sk,
> >> > empty = 0;
> >> > if (shhwtstamps &&
> >> > (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
> >> > + (empty || !skb_is_err_queue(skb)) &&
> >> > ktime_to_timespec_cond(shhwtstamps->hwtstamp, tss.ts + 2)) {
> >>
> >> I find skb->tstamp == 0 easier to understand than the condition on empty.
> >>
> >> Indeed, this is so non-obvious that I would suggest another helper function
> >> skb_is_hwtx_tstamp with a concise comment about the race condition
> >> between tx software and hardware timestamps (as in the last sentence of
> >> the commit message).
> >
> > Should it include also the skb_is_err_queue() check? If it returned
> > true for both TX and RX HW timestamps, maybe it could be called
> > skb_has_hw_tstamp?
>
> For the purpose of documenting why this complex condition exists,
> I would call the skb_is_err_queue in that helper function and make
> it tx + hw specific.
Hm, like this?
if (shhwtstamps &&
(sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
+ (skb_is_hwtx_tstamp(skb) || !skb_is_err_queue(skb)) &&
ktime_to_timespec_cond(shhwtstamps->hwtstamp, tss.ts + 2)) {
where skb_is_hwtx_tstamp() has
return skb->tstamp == 0 && skb_is_err_queue(skb);
I was just not sure about the unnecessary skb_is_err_queue() call.
--
Miroslav Lichvar
