Date: Wed, 11 Sep 2019 15:50:09 -0600 From: Ian Lepore <ian@freebsd.org> To: Alan Somers <asomers@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r352231 - head/lib/libc/sys Message-ID: <63cf915c92b92b07e19337849269ec6bd0dc0d1b.camel@freebsd.org> In-Reply-To: <201909111948.x8BJmWZn092483@repo.freebsd.org> References: <201909111948.x8BJmWZn092483@repo.freebsd.org>
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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
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