145 lines
5.7 KiB
Plaintext
145 lines
5.7 KiB
Plaintext
# @(#)CHANGES 5.1 (Berkeley) 5/11/93
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This new version is almost identical to the timed and timedc code
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that has been shipped for years by a workstation vendor.
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Among the many changes:
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improve `timedc msite` to accept a list of hostnames.
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change slave-masters to answer the packets generated by `timedc msite`
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with the name of the real master, not their own. This makes it
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possible to "chase the chain" of slave servers to the ultimate
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master.
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much improve the log caused by `timedc trace on`:
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-made `timed -t` work.
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-suppression of repeated entries, which both slowed down the daemon
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(sometimes catastrophically) and tended to make disks fill up
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even more quickly.
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-better time stamps on log entries
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-more messages
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-dump information about slaves, master, and so on each time
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a message asking the log be turned on is received, and
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when the log is turned off.
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-fewer CPU cycles
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use a hash table to keep track of slaves, instead of the stupid linear
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list. This becomes handy with hundreds of slaves, instead of
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the original design limit of "a room with a few VAX's."
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separate the main protocol timer from that used to look for other networks
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to master.
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time stamp packets received by the daemon, so that time corrections
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are not made (even more) inaccurate by waiting in the internal,
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timed queue while the daemon is processing other messages.
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made -n and -i work with subnets not named in /etc/networks
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compute the median of the measured clocks, instead of the average
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of "good" times.
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vastly improve the accuracy of the clock difference measure by
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`timedc clockdiff`.
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use adjtime() when possible, and directly set the clock only when
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necessary.
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when the requested adjustment is small, perform only part of it, to
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damp oscillations and improve the long term accuracy of the
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adjustments.
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fix uncounted core-dumps on machines that do not allow dereferencing 0
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in both the daemon and timedc.
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fix "master loop detection".
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fix several cases in which multi-homed masters could get into shouting
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matches, consuming all available network bandwidth and CPU cycles
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(which ever runs out first), and convincing all bystanders to stop
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advancing their own clocks.
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refuse to behave badly when other machines do. Instead of arguing forever,
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go off and sulk when other machines refuse to play by the rules.
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increase the maximum number of clients.
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add "-F host,host2,..." to "freerun" or "trust" only some hosts. This
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is handy both when only some machines should be trusted to let
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root use the `date` command to change time in the network.
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It is also handy when one machine has some other way of adjusting
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its clock, whether NTP or a direct radio or atomic connection.
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"-F localhost" causes `timed` to "trust" only itself.
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It is also handy to build a hierarchy of timed masters crossing
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networks. The TSP protocol has no provision of "goodness of clock",
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no natural way to completely heal network paritions. Judicious
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use of -F or -G can cause each gateway to trust only itself and
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machines closer to a central machine with a radio or atomic clock.
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add #ifdef code that supports NIS "netgroups" of trusted hosts, which
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can be easier to administer than -F.
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add #ifdef code to compute an aged total adjustment. This can be used
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in systems that can make long term changes in their system clock
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frequency, e.g. "timetrim" in the Silicon Graphics kernel.
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Problems observed by others that are unresolved include:
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Practically any users can send to the master TSP messages and this
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way corrupt the reliability of the system. Authentication
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of messages should be provided. Unfortunately, that would
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require changing the protocol with all of the implied
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compatibility problems. Fortunately, the new -F and -G args
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can be used to cause the daemon to ignore time changes from
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untrusted machines.
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MAN. The limit of 1013 on the number of slaves hosts should be doc'ed.
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It should be dynamically allocated with no limit. On a
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large network, one host could possibly master over many
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more than 30 hosts. Given the timers in the code and
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effectively in the protocol, and the time required by each
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master to talk to each slave, it is not practical to have
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more than 200-300 slaves. The master cannot keep up because
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the slave-chatting is single-threaded. when the master
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gets behind, slaves start demanding elections. To
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significantly increase the number of slaves would require
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multi-treading things, and given that a network with more
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than 300 directly addressable machines has worse problems
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than keep the time of day right, not worth worrying about.
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UGLY,CODE. timedc/cmds.c has a lots of repeated code in it.
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**** The first thing is that each command is set up as if it
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were an individual program taking argc and argv. A more
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conventional calling style should be used. I don't think
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any of the routines take more than a couple arguments.
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UGLY. fxn definition syntax does't follow convention:
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has type on same line.
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**** It needs to be fixed at least enough that tags
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will work on it. An entire cleanup might be nice later, but
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is noncritical.
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LOBBY(mildly),CODE: Would be very convenient if date(1) took a
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+-<number> argument to set the time relatively. With
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the advent of timed it is now reasonable to synchronize
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with WWV, which is nearly impossible to do "by hand"
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with just an absolute date, and scripts are too slow.
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format could be +-nn...nn.ss, where the '.' is required
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to remove ambiguity.
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**** If you want to do it go ahead. It sounds useful. As far as
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syntax goes, the normal format for the date should work just
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fine for this. If the date is preceded by a plus or minus,
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the change is relative, otherwise it is absolute.
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Vernon Schryver.
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vjs@sgi.com
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