On Wed, 2019-09-11 at 15:55 -0600, Alan Somers wrote: > On Wed, Sep 11, 2019 at 3:50 PM Ian Lepore <i...@freebsd.org> wrote: > > > On Wed, 2019-09-11 at 19:48 +0000, Alan Somers wrote: > > > Author: asomers > > > Date: Wed Sep 11 19:48:32 2019 > > > New Revision: 352231 > > > URL: https://svnweb.freebsd.org/changeset/base/352231 > > > > > > Log: > > > getsockopt.2: clarify that SO_TIMESTAMP is not 100% reliable > > > > > > When SO_TIMESTAMP is set, the kernel will attempt to attach a > > > > timestamp as > > > ancillary data to each IP datagram that is received on the socket. > > > > However, > > > it may fail, for example due to insufficient memory. In that case the > > > packet will still be received but not timestamp will be attached. > > > > > > Reviewed by: kib > > > MFC after: 3 days > > > Differential Revision: https://reviews.freebsd.org/D21607 > > > > > > Modified: > > > head/lib/libc/sys/getsockopt.2 > > > > > > Modified: head/lib/libc/sys/getsockopt.2 > > > > > > > ============================================================================== > > > --- head/lib/libc/sys/getsockopt.2 Wed Sep 11 19:29:40 2019 > > > > (r352230) > > > +++ head/lib/libc/sys/getsockopt.2 Wed Sep 11 19:48:32 2019 > > > > (r352231) > > > @@ -28,7 +28,7 @@ > > > .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95 > > > .\" $FreeBSD$ > > > .\" > > > -.Dd February 10, 2019 > > > +.Dd September 11, 2019 > > > .Dt GETSOCKOPT 2 > > > .Os > > > .Sh NAME > > > @@ -431,7 +431,8 @@ option is enabled on a > > > .Dv SOCK_DGRAM > > > socket, the > > > .Xr recvmsg 2 > > > -call will return a timestamp corresponding to when the datagram was > > > > received. > > > +call may return a timestamp corresponding to when the datagram was > > > > received. > > > +However, it may not, for example due to a resource shortage. > > > The > > > .Va msg_control > > > field in the > > > > > > > So I guess this actually happened to someone... is it a common thing > > for the timestamp to fail? I ask because ntpd relies on SO_TIMESTAMP > > and if this situation really happens and can persist for a long time, > > ntpd would effectively stop working. > > > > -- Ian > > > > pho discovered how to trigger it. If you start 50 ping processes > simultaneously, sometimes a few will fail. Will ntpd be ok with a single > failure, as long as the timestamp is received correctly in a subsequent > packet? > -Alan
Yeah, nptd is resilient to missing data and intermittent comms, within reason. If it goes hours without getting a timestamp, system time would start to drift. Running 50 concurrent pings sounds like something that won't come up in the real world. :) -- Ian _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
