On 6/4/2020 11:52 AM, Ferruh Yigit wrote: > On 6/3/2020 9:26 PM, Vivien Didelot wrote: >> On Wed, 3 Jun 2020 13:11:39 -0700, Stephen Hemminger >> <step...@networkplumber.org> wrote: >>> On Wed, 3 Jun 2020 18:50:51 +0100 >>> Ferruh Yigit <ferruh.yi...@intel.com> wrote: >>> >>>> On 5/23/2020 6:21 PM, Vivien Didelot wrote: >>>>> When capturing packets into a PCAP file, DPDK currently uses >>>>> microseconds for the timestamp. But libpcap supports interpreting >>>>> tv_usec as nanoseconds depending on the file timestamp precision. >>>>> >>>>> To support this, use PCAP_TSTAMP_PRECISION_NANO when creating the >>>>> empty PCAP file as specified by PCAP_OPEN_DEAD(3PCAP) and implement >>>>> nanosecond timeval addition. This also ensures that the precision >>>>> reported by capinfos is nanoseconds (9). >>>> >>>> Overall good idea and patch looks good. >>>> >>>> Only concern is change in the libpcap dependency. Do you know which libpcap >>>> version supports 'PCAP_TSTAMP_PRECISION_NANO'? >>>> If a user of pcap PMD updates to latest DPDK and the environment doesn't >>>> have >>>> new version of the libpcap, this change will require an environment update >>>> and >>>> this may or may not be easy to do. That is why not sure if the updates >>>> require >>>> dependency change should wait for the LTS or not. >>>> >>>> Another things is the backward compatibility, as far as I understand the >>>> pcap >>>> file recorded with nanosecond precision can be read and parsed without >>>> problem >>>> by old application that doesn't know the nanosecond precision, but can you >>>> please confirm this? >>> >>> We should do pcapng instead of doing the pcap with nano timestamp. >>> My impression is that libpcap is a dormant project at this point, and the >>> finer grain timestamp is a hack that is only in some verisions. >>> That was one of the reasons pcapng started. >> >> Reading tv_usec as nanoseconds has been supported for years in libpcap. >> >> For instance PCAP_TSTAMP_PRECISION_NANO was introduced in ba89e4a18e8b >> ("Make timestamps precision configurable") on May 17, 2013. > > Thanks for the commit info, it looks like this support exists since > libpcap-1.5.0, and even CentOS 7 has libpcap-1.5.3-xx so looks safe to > proceed. >
But it may be good to mention from the change in the release notes, can you please update the release notes (doc/guides/rel_notes/release_20_08.rst) in next version of the patch.