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Unix/Linux 网络时间协议版本3 Network Time Protocol Version 3 (NTP) distribution for Unix systems

Replied: Fri, 27 Mar 1998 01:29:51 -0500
Replied: "[e-mail] "
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          26 Mar 1998 20:18 EST
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Date: Thu, 26 Mar 1998 17:18:09 -0800 (PST)
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From: Jonathan Stone <[e-mail]>
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Path: Kowhai.Stanford.EDU!jonathan
Newsgroups: comp.protocols.time.ntp
To: "David L. Mills" <[e-mail]>
Cc: [e-mail]
Subject: Portability paranoia patches for adding TIOCDCDTIMESTAMP
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Organization: Stanford Distributed Systems Grop
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[posted to comp.protocols.time.ntp, for inspection, and emailed]

I've implemented TIOCDCDTIMESTAMP in NetBSD, with the same semantics
and name as FreeBSD.  Looking at the 3-5.92 code, if the system
headers define TIOCDDCDTIMESTAMP, xntpd/ntp_refclock.c assumes the
ioctl() will always succeed.  The older, pre-DIOCDCDTIMESTAMP code is
#ifdef'ed out

The following patch changes the test for TIOCDDCDTIMESTAMP usage from
compile-time to run-time. This is a small piece of paranoia, to make
xntpd work even if the source has TIOCDDCDTIMESTAMP, but the kernel
doesn't. It also increases backward portabiility.

I'd like to put these changes into the NetBSD-distributed version of
xntp, for ease of binary distributions. It'd be nice, but not
necessary, if they got pulled into the canonical source.

I havent actually tried this on a refclock yet, eihter with or without
TIOCDCDTIMESTAMP, but it seems utterly straightforward to fall back
from the inkernel timestamp to the old method, if and only if the
kernel pukes on the TIOCDCDTIMESTAMP ioctl().  

I'd be grateful for any advice to the contrary.




Index: xntpd/ntp_refclock.c
===================================================================
RCS file: /cvsroot/src/usr.sbin/xntp/xntpd/ntp_refclock.c,v
retrieving revision 1.3
diff -c -r1.3 ntp_refclock.c
*** ntp_refclock.c	1998/03/06 18:17:22	1.3
--- ntp_refclock.c	1998/03/27 01:10:05
***************
*** 722,729 ****
  		} else
  			trtmp = rbufp->recv_time;
  	}
! 
! #else /* TIOCDCDTIMESTAMP */
  	if (dpend >= dpt + 8) {
  		if (buftvtots(dpend - 8, &tstmp)) {
  			L_SUB(&trtmp, &tstmp);
--- 722,730 ----
  		} else
  			trtmp = rbufp->recv_time;
  	}
! 	else
! 	/* XXX fallback to old method if kernel refuses TIOCDCDTIMESTAMP */
! #endif  /* TIOCDCDTIMESTAMP */
  	if (dpend >= dpt + 8) {
  		if (buftvtots(dpend - 8, &tstmp)) {
  			L_SUB(&trtmp, &tstmp);
***************
*** 746,752 ****
  				trtmp = rbufp->recv_time;
  		}
  	}
- #endif /* TIOCDCDTIMESTAMP */
  
  	/*
  	 * Edit timecode to remove control chars. Don't monkey with the
--- 747,752 ----