Subject: Re: [PATCH net-next] packet: move hw/sw timestamp extraction into a small helper

From: Daniel Borkmann <[email-masked]>
Date: Mon, 15 Apr 2013 19:02:03 +0200

On 04/15/2013 06:12 PM, Willem de Bruijn wrote:
> On Mon, Apr 15, 2013 at 7:41 AM, Daniel Borkmann <[email-masked]> wrote:
>> This patch introduces a small helper function, that is used by AF_PACKET.
>> Based on the flags that are passed, it extracts the packet timestamp in
>> the receive path. This is merely a refactoring to remove some duplicate
>> code in tpacket_rcv(), make it more readable, and to enable others to use
>> this function as well.
>
> Good idea. I noticed that while browsing the code over the weekend, too.
>
> One question I have is whether the code warrants adding a static
> inline to skbuff.h. Regular socket paths do not use the test, as they
> return all timestamps together.

(See below.)

>> Cc: Willem de Bruijn <[email-masked]>
>> Signed-off-by: Daniel Borkmann <[email-masked]>
>> ---
>>   include/linux/skbuff.h | 20 ++++++++++++++++++++
>>   net/packet/af_packet.c | 38 ++++----------------------------------
>>   2 files changed, 24 insertions(+), 34 deletions(-)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index e27d1c7..d0d436f 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -33,6 +33,7 @@
>>   #include <linux/dma-mapping.h>
>>   #include <linux/netdev_features.h>
>>   #include <net/flow_keys.h>
>> +#include <linux/net_tstamp.h>
>>
>>   /* Don't change this without changing skb_csum_unnecessary! */
>>   #define CHECKSUM_NONE 0
>> @@ -739,6 +740,25 @@ static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
>>          return &skb_shinfo(skb)->hwtstamps;
>>   }
>>
>> +static inline struct timespec skb_get_tstamp(struct sk_buff *skb,
>> +                                            unsigned int flags)
>> +{
>> +       struct skb_shared_hwtstamps *ts = skb_hwtstamps(skb);
>> +
>> +       if ((flags & SOF_TIMESTAMPING_SYS_HARDWARE) && ts->syststamp.tv64)
>
> Also, packet sockets use the flags these SOF_... constants passed from
> userspace directly, but regular socket paths convert this into socket
> flags SOCK_..., so this code is more packet socket specific than it
> seems. See __sock_recv_timestamp. I'd keep the function in
> net/packet/af_packet.c solely for this reason, or add a comment.

Hm, right. I do not really see a reason why we need to maintain this twice
(introduced by 614f60fa9 ``packet_mmap: expose hw packet timestamps to network
packet capture utilities'').

This could also have been implemented actually with normal SOCK_ flags, i.e.
since we use sock_tx_timestamp() which uses SOCK_ flags. I will respin and try
to address that.

>> +               return ktime_to_timespec(ts->syststamp);
>> +       else if ((flags & SOF_TIMESTAMPING_RAW_HARDWARE) && ts->hwtstamp.tv64)
>> +               return ktime_to_timespec(ts->hwtstamp);
>> +       else if (skb->tstamp.tv64)
>> +               return ktime_to_timespec(skb->tstamp);
>> +       else {
>> +               struct timespec tc;
>> +
>> +               getnstimeofday(&tc);
>> +               return tc;
>> +       }
>> +}
>> +
>>   /**
>>    *     skb_queue_empty - check if a queue is empty
>>    *     @list: queue head
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index 77d71f8..2a2a62e 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -1681,9 +1681,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>          unsigned long status = TP_STATUS_USER;
>>          unsigned short macoff, netoff, hdrlen;
>>          struct sk_buff *copy_skb = NULL;
>> -       struct timeval tv;
>>          struct timespec ts;
>> -       struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
>>
>>          if (skb->pkt_type == PACKET_LOOPBACK)
>>                  goto drop;
>> @@ -1767,24 +1765,16 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>
>>          skb_copy_bits(skb, 0, h.raw + macoff, snaplen);
>>
>> +       ts = skb_get_tstamp(skb, po->tp_tstamp);
>> +
>>          switch (po->tp_version) {
>>          case TPACKET_V1:
>>                  h.h1->tp_len = skb->len;
>>                  h.h1->tp_snaplen = snaplen;
>>                  h.h1->tp_mac = macoff;
>>                  h.h1->tp_net = netoff;
>> -               if ((po->tp_tstamp & SOF_TIMESTAMPING_SYS_HARDWARE)
>> -                               && shhwtstamps->syststamp.tv64)
>> -                       tv = ktime_to_timeval(shhwtstamps->syststamp);
>> -               else if ((po->tp_tstamp & SOF_TIMESTAMPING_RAW_HARDWARE)
>> -                               && shhwtstamps->hwtstamp.tv64)
>> -                       tv = ktime_to_timeval(shhwtstamps->hwtstamp);
>> -               else if (skb->tstamp.tv64)
>> -                       tv = ktime_to_timeval(skb->tstamp);
>> -               else
>> -                       do_gettimeofday(&tv);
>> -               h.h1->tp_sec = tv.tv_sec;
>> -               h.h1->tp_usec = tv.tv_usec;
>> +               h.h1->tp_sec = ts.tv_sec;
>> +               h.h1->tp_usec = ts.tv_nsec / NSEC_PER_USEC;
>>                  hdrlen = sizeof(*h.h1);
>>                  break;
>>          case TPACKET_V2:
>> @@ -1792,16 +1782,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>                  h.h2->tp_snaplen = snaplen;
>>                  h.h2->tp_mac = macoff;
>>                  h.h2->tp_net = netoff;
>> -               if ((po->tp_tstamp & SOF_TIMESTAMPING_SYS_HARDWARE)
>> -                               && shhwtstamps->syststamp.tv64)
>> -                       ts = ktime_to_timespec(shhwtstamps->syststamp);
>> -               else if ((po->tp_tstamp & SOF_TIMESTAMPING_RAW_HARDWARE)
>> -                               && shhwtstamps->hwtstamp.tv64)
>> -                       ts = ktime_to_timespec(shhwtstamps->hwtstamp);
>> -               else if (skb->tstamp.tv64)
>> -                       ts = ktime_to_timespec(skb->tstamp);
>> -               else
>> -                       getnstimeofday(&ts);
>>                  h.h2->tp_sec = ts.tv_sec;
>>                  h.h2->tp_nsec = ts.tv_nsec;
>>                  if (vlan_tx_tag_present(skb)) {
>> @@ -1822,16 +1802,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>                  h.h3->tp_snaplen = snaplen;
>>                  h.h3->tp_mac = macoff;
>>                  h.h3->tp_net = netoff;
>> -               if ((po->tp_tstamp & SOF_TIMESTAMPING_SYS_HARDWARE)
>> -                               && shhwtstamps->syststamp.tv64)
>> -                       ts = ktime_to_timespec(shhwtstamps->syststamp);
>> -               else if ((po->tp_tstamp & SOF_TIMESTAMPING_RAW_HARDWARE)
>> -                               && shhwtstamps->hwtstamp.tv64)
>> -                       ts = ktime_to_timespec(shhwtstamps->hwtstamp);
>> -               else if (skb->tstamp.tv64)
>> -                       ts = ktime_to_timespec(skb->tstamp);
>> -               else
>> -                       getnstimeofday(&ts);
>>                  h.h3->tp_sec  = ts.tv_sec;
>>                  h.h3->tp_nsec = ts.tv_nsec;
>>                  hdrlen = sizeof(*h.h3);
>> --
>> 1.7.11.7
>>