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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: Mon, 10 Mar 1997 23:15:22 -0500
Replied: ""Edward J. Huff" <[e-mail]> [e-mail], [e-mail], [e-mail]"
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          11 Mar 97 3:51 GMT
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	id WAA06579; Mon, 10 Mar 1997 22:46:54 -0500
Date: Mon, 10 Mar 1997 22:46:54 -0500
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From: "Edward J. Huff" <[e-mail]>
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    [e-mail]
In-reply-to: <[e-mail]> ([e-mail])
Subject: Adding volatile to variables shared with signal handlers

Attached find a patch which adds volatile to variables modified by
the input_handler() signal handler.  I might have missed some.

>   Is the tickadj thing settled? Is the nonblocking I/O thing settled?
>   There are so many details floating around, I'm not sure everything is
>   settled. I take it all is documented in the changelog, but the important
>   things should probably go in the html pages.
>
>   Dave

Guys,

I was just reading in revised K&R about "const" qualifiers and noticed
the definition of "volatile".  Variables shared between mainline code
and signal handlers should be marked volatile.  (that is, modified by
signal handlers).  (As someone said earlier in the newsgroup.  I
thought it wasn't enought to fix the bug -- it wasn't -- but now that
the bug is fixed, volatile is still needed).

I suppose this doesn't need to be done instantly.  I doubt that it
will change code except maybe when compiled with -O3.  But it
constitutes a lurking bug that ought to be fixed before a compiler
comes along that exposes it.

I've never tried compiling xntpd with gcc -O3, but I use it routinely
for programs here.  I don't know if it would result in optimizations
that are invalid without volatile.

I cut input_handler out of ntp_io.c and tried compiling it to see what
global/static symbols it references.  Some of these should be
volatile.  e.g. activefds shouldn't be because it is only referenced,
not modified.  (I kept the #include statements and the input_handler
function).

This also assumes there aren't any global variables declared in any of
the header files needed to get input_handler to compile.  Do any of
you have a better way of finding static/globals used by a function?
Also, this is only for xntpd input_handler.  I didn't look in the
other programs.  And I think none of the functions called from within
input_handler modify any static or global variables.  Is this correct?

Changes would be required in modules other than ntp_io.c.  For
instance, extern u_long packets_ignored; should be extern volatile
u_long packets_ignored; in ntp_request.c.

I guess the volatile for inter_list[i].received belongs inside the
struct declaration for struct interface.

These variables were listed as undefined by gcc when compiling just
the #includes and the input_handler() function.  I looked at the code
to see if they are modified:

handler_calls    MODIFIED
activefds        INPUT ONLY
maxactivefd      INPUT ONLY
handler_pkts     MODIFIED
refio            INPUT ONLY
free_recvbufs    MODIFIED
packets_dropped  MODIFIED
freelist         MODIFIED
fulllist         MODIFIED
beginlist	 MODIFIED
full_recvbufs    MODIFIED
packets_received MODIFIED
ninterfaces      INPUT ONLY
inter_list       MODIFIED?  e.g. inter_list[i].received++
debug            INPUT ONLY
packets_ignored  MODIFIED

So I guess if I got this far, I may as well produce the patches.
I've compiled these but I didn't test it.  Some compilers might
not like volatile, so there is probably more work to do.


carbon% foreach f ( `find . -mtime -2 -type f` )
? diff -c $f ../../xntp3-5.89.8/$f
? end
*** ./include/ntp.h	Mon Mar 10 22:18:04 1997
--- ../../xntp3-5.89.8/./include/ntp.h	Wed Jan  1 15:05:50 1997
***************
*** 225,231 ****
  	char name[8];		/* name of interface */
  	int flags;		/* interface flags */
  	int last_ttl;		/* last TTL specified */
! 	volatile long received;		/* number of incoming packets */
  	long sent;		/* number of outgoing packets */
  	long notsent;		/* number of send failures */
  };
--- 225,231 ----
  	char name[8];		/* name of interface */
  	int flags;		/* interface flags */
  	int last_ttl;		/* last TTL specified */
! 	long received;		/* number of incoming packets */
  	long sent;		/* number of outgoing packets */
  	long notsent;		/* number of send failures */
  };
*** ./xntpd/ntp_io.c	Mon Mar 10 22:16:03 1997
--- ../../xntp3-5.89.8/./xntpd/ntp_io.c	Tue Feb 18 20:00:49 1997
***************
*** 109,120 ****
  /*
   * Memory allocation
   */
! volatile u_long full_recvbufs;		/* number of recvbufs on fulllist */
! volatile u_long free_recvbufs;		/* number of recvbufs on freelist */
  
! volatile static	struct recvbuf *freelist;	/* free buffers */
! volatile static	struct recvbuf *fulllist;	/* lifo buffers with data */
! volatile static	struct recvbuf *beginlist;	/* fifo buffers with data */
  
  u_long total_recvbufs;		/* total recvbufs currently in use */
  u_long lowater_additions;	/* number of times we have added memory */
--- 109,120 ----
  /*
   * Memory allocation
   */
! u_long full_recvbufs;		/* number of recvbufs on fulllist */
! u_long free_recvbufs;		/* number of recvbufs on freelist */
  
! static	struct recvbuf *freelist;	/* free buffers */
! static	struct recvbuf *fulllist;	/* lifo buffers with data */
! static	struct recvbuf *beginlist;	/* fifo buffers with data */
  
  u_long total_recvbufs;		/* total recvbufs currently in use */
  u_long lowater_additions;	/* number of times we have added memory */
***************
*** 125,138 ****
  /*
   * Other statistics of possible interest
   */
! volatile u_long packets_dropped;	/* total number of packets dropped on reception */
! volatile u_long packets_ignored;	/* packets received on wild card interface */
! volatile u_long packets_received;	/* total number of packets received */
  u_long packets_sent;	/* total number of packets sent */
  u_long packets_notsent;	/* total number of packets which couldn't be sent */
  
! volatile u_long handler_calls;	/* number of calls to interrupt handler */
! volatile u_long handler_pkts;	/* number of pkts received by handler */
  u_long io_timereset;	/* time counters were reset */
  
  /*
--- 125,138 ----
  /*
   * Other statistics of possible interest
   */
! u_long packets_dropped;	/* total number of packets dropped on reception */
! u_long packets_ignored;	/* packets received on wild card interface */
! u_long packets_received;	/* total number of packets received */
  u_long packets_sent;	/* total number of packets sent */
  u_long packets_notsent;	/* total number of packets which couldn't be sent */
  
! u_long handler_calls;	/* number of calls to interrupt handler */
! u_long handler_pkts;	/* number of pkts received by handler */
  u_long io_timereset;	/* time counters were reset */
  
  /*
*** ./xntpd/ntp_request.c	Mon Mar 10 22:14:05 1997
--- ../../xntp3-5.89.8/./xntpd/ntp_request.c	Mon Jan 13 19:56:11 1997
***************
*** 1050,1066 ****
  	 * Importations from the io module
  	 */
  	extern u_long io_timereset;
! 	volatile extern u_long full_recvbufs;
! 	volatile extern u_long free_recvbufs;
  	extern u_long total_recvbufs;
  	extern u_long lowater_additions;
! 	volatile extern u_long packets_dropped;
! 	volatile extern u_long packets_ignored;
! 	volatile extern u_long packets_received;
  	extern u_long packets_sent;
  	extern u_long packets_notsent;
! 	volatile extern u_long handler_calls;
! 	volatile extern u_long handler_pkts;
  
  	io = (struct info_io_stats *)prepare_pkt(srcadr, inter, inpkt,
  	    sizeof(struct info_io_stats));
--- 1050,1066 ----
  	 * Importations from the io module
  	 */
  	extern u_long io_timereset;
! 	extern u_long full_recvbufs;
! 	extern u_long free_recvbufs;
  	extern u_long total_recvbufs;
  	extern u_long lowater_additions;
! 	extern u_long packets_dropped;
! 	extern u_long packets_ignored;
! 	extern u_long packets_received;
  	extern u_long packets_sent;
  	extern u_long packets_notsent;
! 	extern u_long handler_calls;
! 	extern u_long handler_pkts;
  
  	io = (struct info_io_stats *)prepare_pkt(srcadr, inter, inpkt,
  	    sizeof(struct info_io_stats));
carbon%