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Date: Sat, 14 May 2016 11:47:22 -0700 From: Guy Harris <guy@...m.mit.edu> To: Richard Cochran <richardcochran@...il.com> Cc: Network Development <netdev@...r.kernel.org> Subject: Re: What ixgbe devices support HWTSTAMP_FILTER_ALL for hardware time stamping? On May 14, 2016, at 12:30 AM, Richard Cochran <richardcochran@...il.com> wrote: > On Fri, May 13, 2016 at 04:12:52PM -0700, Guy Harris wrote: >> The Linux implementation currently implements the inquiry by doing a >> ETHTOOL_GET_TS_INFO SIOETHTOOL ioctl and looking at the >> so_timestamping bits, if the linux/ethtool.h header defines >> ETHTOOL_GET_TS_INFO and the ioctl succeeds on the device. > > So far, so good. > >> This is inadequate - as libpcap requests hardware time stamping for >> all packets, it should also check whether HWTSTAMP_FILTER_ALL is set >> in rx_filters, and only offer hardware time stamping if it's set. > > The SO_TIMESTAMPING and SIOCSHWTSTAMP interfaces predate > ETHTOOL_GET_TS_INFO, and they work fine without it. Applications > should simply use SIOCSHWTSTAMP to request the mode that they need and > check the result. So if you have a GUI application for packet capture, with a combo box to select the type of time stamping, should it: 1) regardless of whether ETHTOOL_GET_TS_INFO is available, open the adapter, try each of the time stamp types to see whether it works, and show a combo box based on that; 2) use ETHTOOL_GET_TS_INFO if available; 3) offer all possibilities regardless of whether they work with the adapter or not, and just report an error for possibilities that don't work? My preference is 2) - which is the main reason why libpcap offers "what possibilities are available?" APIs, not just "request this possibility" APIs.
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