From:	"Ulrich Windl" <ulrich.windl@rz.uni-regensburg.de>
To:	linux-kernel@vger.rutgers.edu
Date:	Tue, 16 Feb 1999 09:28:12 +0100
Subject: RFD: nanoseconds in the kernel, POSIX.4, cleanups

Hello,

I began to convert kernel/time.c to nanoseconds (i.e. xtime is struct 
timespec instead of struct timeval) now. There are easy changes and 
more diffucult ones. The stuff in kernel/time.c should be rather easy.

The architecture-specific kernel/time.c is more tricky, especially as 
I don't know much about all these.

Basically the old functions should be still there, together with new 
ones. For example we have an old gettimeoffset() that returns 
microseconds, but we'll need a new one that return nanoseconds.

There are two solutions: 1) Keep the old functions, and derive the 
new ones by simply scaling-up the old stuff. 2) Make new functions in 
addition to the old ones 3) Make new fuctions for nanoseconds, and 
map the old ones to the new ones.

Of course I'd vote for "3)".

A rather unrelated issue is that of naming: Having in mind the 
ability to support more of POSIX.4, we could have clock_gettime() to 
get the time in nanoseconds, and clock_settime() to set the time. 
clock_getres() that returns the resolution seems tricky if done 
correctly. (Or should I simply assume "1ns"?)

Is anybody interested in helping me or testing this very experimental 
stuff soon? (Together with other changes made for the NTPv4 clock 
model, binary compatibility with old executables had to be broken: 
especially adjtime() and ADJ_OFFSET_SINGLESHOT occupy a different bit 
position now, causing the old adjtime() to be a no-op. I took the 
chance to cleanup the whole mess.)

BTW: Do you think external modules should need access to all the time 
variables? These were declared in <linux/timex.h> before, but they 
are no longer, because there were too many changes. Despite of that I 
think that "clients" should use the official interface defined by 
functions.

I'm also considering why the fuction to set the time is currently in 
the architecture-specific arch-*/kernel/time.c. It only seems to need 
the fast timeoffset, but it could be exported from there. I'll have 
to check when I'm that far.

Opinions, please!

Ulrich


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