[RFC] net : add tx timestamp to packet mmap.

This patch allow to generate tx timestamps of packets sent by the packet mmap interface.

Actually, you can't get tx timestamps with the sample code below.

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 it back to the user ?

Thanks for your comments.

/* BEGIN OF SAMPLE CODE */
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);
      fprintf(stderr, "SCM_TIMESTAMPING available\n");
    }
  else if (cmsg->cmsg_level == SOL_PACKET && cmsg->cmsg_type == PACKET_TX_TIMESTAMP)
      {
        ts = *(struct timespec *)CMSG_DATA(cmsg);
        fprintf(stderr, "PACKET_TX_TIMESTAMP available\n");
      }
} 
/* END OF SAMPLE CODE */

Signed-off-by: Paul Chavent <redacted>
---
 net/packet/af_packet.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e639645..948748b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c

@@ -1857,6 +1857,10 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 	void *data;
 	int err;
 
+	err = sock_tx_timestamp(&po->sk, &skb_shinfo(skb)->tx_flags);
+	if (err < 0)
+		return err;
+
 	ph.raw = frame;
 
 	skb->protocol = proto;

-- 
1.7.12.1