svn commit: r352231 - head/lib/libc/sys

[Cy Schubert]

In message <63cf915c92b92b07e19337849269ec6bd0dc0d1b.camel at freebsd.org>, 
Ian Le
pore writes:
> 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 a
> s
> >   ancillary data to each IP datagram that is received on the socket. Howeve
> r,
> >   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	(r35223
> 0)
> > +++ head/lib/libc/sys/getsockopt.2	Wed Sep 11 19:48:32 2019	(r35223
> 1)
> > @@ -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 receiv
> ed.
> > +call may return a timestamp corresponding to when the datagram was receive
> d.
> > +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.

This reminds me, something that's been on my plate for a couple of weeks. 
Our NTP upline pinged me a few weeks ago regarding IEEE 1588 driver support 
for NICs with hardware support. Linux already has it. I was told that 
someone hrtr has attempted this but that the results weren't optimal. 
That's all I know. Should I open discussion on arch@?


-- 
Cheers,
Cy Schubert <Cy.Schubert at cschubert.com>
FreeBSD UNIX:  <cy at FreeBSD.org>   Web:  http://www.FreeBSD.org

	The need of the many outweighs the greed of the few.