Re: [PATCH v2] net: packetmmap: fix only tx timestamp on request

[Richard Sanger <rsanger@wand.net.nz>]

On Thu, May 13, 2021 at 2:24 AM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Tue, May 11, 2021 at 9:32 PM Richard Sanger <rsanger@wand.net.nz> wrote:
> >
> > The packetmmap tx ring should only return timestamps if requested via
> > setsockopt PACKET_TIMESTAMP, as documented. This allows compatibility
> > with non-timestamp aware user-space code which checks
> > tp_status == TP_STATUS_AVAILABLE; not expecting additional timestamp
> > flags to be set in tp_status.
> >
> > Fixes: b9c32fb27170 ("packet: if hw/sw ts enabled in rx/tx ring, report which ts we got")
> > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> > Signed-off-by: Richard Sanger <rsanger@wand.net.nz>
>
> Code LGTM.
>
> It would be good to capture more of the context: when these spurious
> timestamps can appear (network namespaces) and as of which commit (the
> one that changes orphaning). As is, I would not be able to understand
> the issue addressed from this commit message alone.
>
> Instead of adding context to the commit, you could also add a Link tag
> to the archived email thread, if you prefer.
>
> And perhaps: [PATCH net v3] net/packet: return software transmit
> timestamp only when requested
>

Ahh, looks like this patch has just been merged in.

For anyone looking for more details they are in this thread:
https://lore.kernel.org/netdev/1620085579-5646-1-git-send-email-rsanger@wand.net.nz/

>
> > ---
> >  net/packet/af_packet.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > index ba96db1..ae906eb 100644
> > --- a/net/packet/af_packet.c
> > +++ b/net/packet/af_packet.c
> > @@ -422,7 +422,8 @@ static __u32 tpacket_get_timestamp(struct sk_buff *skb, struct timespec64 *ts,
> >             ktime_to_timespec64_cond(shhwtstamps->hwtstamp, ts))
> >                 return TP_STATUS_TS_RAW_HARDWARE;
> >
> > -       if (ktime_to_timespec64_cond(skb->tstamp, ts))
> > +       if ((flags & SOF_TIMESTAMPING_SOFTWARE) &&
> > +           ktime_to_timespec64_cond(skb->tstamp, ts))
> >                 return TP_STATUS_TS_SOFTWARE;
> >
> >         return 0;
> > @@ -2340,7 +2341,12 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
> >
> >         skb_copy_bits(skb, 0, h.raw + macoff, snaplen);
> >
> > -       if (!(ts_status = tpacket_get_timestamp(skb, &ts, po->tp_tstamp)))
> > +       /* Always timestamp; prefer an existing software timestamp taken
> > +        * closer to the time of capture.
> > +        */
> > +       ts_status = tpacket_get_timestamp(skb, &ts,
> > +                                         po->tp_tstamp | SOF_TIMESTAMPING_SOFTWARE);
> > +       if (!ts_status)
> >                 ktime_get_real_ts64(&ts);
> >
> >         status |= ts_status;
> > --
> > 2.7.4
> >