netdev - Tx timestamp for packet mmap.

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Date:	Fri, 07 Dec 2012 16:28:29 +0100
From:	Paul Chavent <Paul.Chavent@...ra.fr>
To:	netdev@...r.kernel.org
Subject: Tx timestamp for packet mmap.

Hi.

I would like to be able to get tx timestamps of packets sent by the 
packet mmap interface...

Actually, I try to get them with the sample code below.

The problem is that it doesn't work without the joined patch.

I wonder if my current implementation is good. And if not, how should i 
get the timestamps ?

Wouldn't be a good idea to put timestamps in the ring buffer frame 
before give back the frame to the user ?

Thanks for your help and advices.

Paul.

8<-------------------------------


   struct timespec ts = {0,0};
   struct sockaddr from_addr;
   static uint8_t tmp_data[256];
   struct iovec msg_iov = {tmp_data, sizeof(tmp_data)};
   static uint8_t cmsg_buff[256];
   struct msghdr msghdr = {&from_addr, sizeof(from_addr),
                           &msg_iov, 1,
                           cmsg_buff, sizeof(cmsg_buff),
                           0};
   ssize_t err = recvmsg(itf->sock_fd, &msghdr, MSG_ERRQUEUE);
   if(err < 0)
     {
       perror("recvmsg failed");
       return -1;
     }

   struct cmsghdr *cmsg;
   for(cmsg = CMSG_FIRSTHDR(&msghdr); cmsg != NULL; cmsg = 
CMSG_NXTHDR(&msghdr, cmsg))
     {
       if(cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == 
SCM_TIMESTAMPING)
         {
           ts = *(struct timespec *)CMSG_DATA(cmsg);
#if !defined(NDEBUG)
           if(itf->debug)
             {
               fprintf(stderr, "SCM_TIMESTAMPING available\n");
             }
#else
           break;
#endif
         }
       else if (cmsg->cmsg_level == SOL_PACKET && cmsg->cmsg_type == 
PACKET_TX_TIMESTAMP)
         {
           ts = *(struct timespec *)CMSG_DATA(cmsg);
#if !defined(NDEBUG)
           if(itf->debug)
             {
               fprintf(stderr, "PACKET_TX_TIMESTAMP available\n");
             }
#else
           break;
#endif
         }
     }

View attachment "0002-net-add-tx-timestamp-to-packet-mmap.patch" of type "text/x-patch" (764 bytes)