On Fri, May 19, 2017 at 6:00 AM, Miroslav Lichvar <mlich...@redhat.com> wrote:
> On Thu, May 18, 2017 at 04:16:26PM -0400, Willem de Bruijn wrote:
>> On Thu, May 18, 2017 at 9:06 AM, Miroslav Lichvar <mlich...@redhat.com>
>> wrote:
>> > +/* On transmit, software and hardware timestamps are returned
>> > independently.
>> > + * As the two skb clones share the hardware timestamp, which may be
>> > updated
>> > + * before the software timestamp is received, a hardware TX timestamp may
>> > be
>> > + * returned only if there is no software TX timestamp. A false software
>> > + * timestamp made for SOCK_RCVTSTAMP when a real timestamp is missing must
>> > + * be ignored.
>>
>> Please expand on why this case can be ignored. It is quite subtle. How about
>> something like
>>
>> *
>> * A false software timestamp is one made inside the __sock_recv_timestamp
>> * call itself. These are generated whenever SO_TIMESTAMP(NS) is enabled
>> * on the socket, even when the timestamp reported is for another option, such
>> * as hardware tx timestamp.
>> *
>> * Ignore these when deciding whether a timestamp source is hw or sw.
>> */
>
> That seems a bit too verbose to me. :) Would the following work?
>
> /* On transmit, software and hardware timestamps are returned independently.
> * As the two skb clones share the hardware timestamp, which may be updated
> * before the software timestamp is received, a hardware TX timestamp may be
> * returned only if there is no software TX timestamp. Ignore false software
> * timestamps, which may be made in the __sock_recv_timestamp() call when the
> * option SO_TIMESTAMP(NS) is enabled on the socket, even when the skb has a
> * hardware timestamp.
> */
Looks great, thanks.
>
>> > +static bool skb_is_swtx_tstamp(const struct sk_buff *skb,
>> > + const struct sock *sk, int false_tstamp)
>> > +{
>> > + if (false_tstamp && sk->sk_tsflags & SOF_TIMESTAMPING_OPT_TX_SWHW)
>>
>> Also, why is it ignored only for the new mode?
>
> Good point. That should not be there. The function can be now reduced
> to a single line again. I originally tried a different approach,
> disabling false timestamps in the new mode, but then I thought it's
> better to not complicate it unnecessarily and keep it consistent.
>
> --
> Miroslav Lichvar
