Re: ext4 features

From: Bill Davidsen
Date: Wed Jul 05 2006 - 17:12:56 EST


Trond Myklebust wrote:

On Wed, 2006-07-05 at 08:59 -0400, J. Bruce Fields wrote:


On Wed, Jul 05, 2006 at 08:24:29AM -0400, Bill Davidsen wrote:


Theodore Tso wrote:


Some of the ideas which have been tossed about include:

* nanosecond timestamps, and support for time beyond the 2038


The 2nd one is probably more urgent than the first. I can see a general benefit from timestamp in ms, beyond that seems to be a specialty requirement best provided at the application level rather than the bits of a trillion inodes which need no such thing.


What's urgently needed for NFS (and I suspect for most other
applications demanding higher timestamps) isn't really nanosecond
precision so much as something that's guaranteed to increase whenever
the file changes.



NFS doesn't necessarily require monotonicity either. The only real
requirement that knfsd has is that the timestamp needs to change every
time the file data (mtime+ctime) and/or metadata (ctime only) is
changed.

Applications like 'make' OTOH, probably would be happier if the
timestamps are guaranteed to be monotonic.


Consider the case where the build machine reads source from one network filesystem and write the binary result to another on another machine. If you know that I have the kernel source on a file server, do the compiles on a compute server, and store the binaries on three test machines for evaluation, you might guess this really can happen. Just increasing the timestamp may not solve the problem, unless you have a system call to set timestamp over network f/s, like a high resolution touch.

It's a problem when there are multiple times involved.

--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979

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