tcpdump mailing list archives
Re: Hardware Timestamping Problem
From: Guy Harris <guy () alum mit edu>
Date: Thu, 9 Jun 2016 16:35:58 -0700
On Jun 9, 2016, at 4:09 PM, Guenter Ebermann <guenter.ebermann () googlemail com> wrote:
Am 10.06.2016 um 00:13 schrieb Guy Harris <guy () alum mit edu>: But that doesn't mean that the packets time stamped by the hardware when transmitted will be delivered to the PF_PACKET sockets used by libpcap *with the hardware time stamp as the time stamp*. In order make that happen, if hardware transmit time stamping is enabled for a PF_PACKET socket: dev_queue_xmit_nit() will *NOT* deliver, to that socket, packets queued for transmission; when the hardware says "I've transmitted these packets" (and time-stamped them), the driver will take those packets and deliver them to all PF_PACKET sockets with hardware transmit time stamping enabled? If those aren't done, then code processing packets from a PF_PACKET socket will get a mix of packets with software time stamps (packets sent by the machine on which that code is running) and hardware time stamps (packets received by that machine). I don't see any obvious code in dev_queue_xmit_nit() to avoid delivering packets to sockets that have requested hardware time stamping, so the first of those statements doesn't appear to be true; is the second one true?Perhaps I am wrong, but it seems the drivers deliver the sent packets, including the hardware-timestamp, to the error queue of the socket.
And those don't just get delivered to the socket on which the packet was sent, they get delivered to *all* sockets, including the PF_PACKET sockets used for traffic capture? If not, then the second statement doesn't appear to be true, either. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Re: Hardware Timestamping Problem, (continued)
- Re: Hardware Timestamping Problem Christian Rupp (Jun 08)
- Re: Hardware Timestamping Problem Guy Harris (Jun 08)
- Re: Hardware Timestamping Problem Christian (Jun 09)
- Re: Hardware Timestamping Problem Michael Richardson (Jun 08)
- Re: Hardware Timestamping Problem Guenter Ebermann (Jun 08)
- Re: Hardware Timestamping Problem Michael Richardson (Jun 09)
- Re: Hardware Timestamping Problem Christian (Jun 09)
- Re: Hardware Timestamping Problem Guenter Ebermann (Jun 09)
- Re: Hardware Timestamping Problem Guy Harris (Jun 09)
- Re: Hardware Timestamping Problem Guenter Ebermann (Jun 09)
- Re: Hardware Timestamping Problem Guy Harris (Jun 09)
- Re: Hardware Timestamping Problem Guenter Ebermann (Jun 09)
- Re: Hardware Timestamping Problem Guy Harris (Jun 09)
- Re: Hardware Timestamping Problem Christian Rupp (Jun 08)