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    SubjectRe: ext4 features
    On Wed, Jul 05, 2006 at 05:12:54PM -0400, Bill Davidsen wrote:
    > J. Bruce Fields wrote:
    > >Or we could add an entirely separate attribute that's guaranteed to
    > >increase whenever the ctime is updated, and that doesn't necessarily
    > >have any connection with time--call it a version number or something.
    > >
    > There are versions in both VMS and the ISO filesystem. I have a sneaking
    > suspicion that those of us who ever use them are few and far between.
    > The other issue is that unless the field is time, programs like make
    > can't really use it, at least without becoming Linux specific.


    > I'm not sure exactly how a "version" value would be used other than
    > detecting the fact that the file had been changed in some way.

    I agree. But "detecting the fact that the file has been changed" is a
    really important use! I think the challenge would be to come up with
    applications that really depend on timestamps and that use them for
    anything *other* than detecting when a file has changed.

    (OK, so make is a special case--it cares not only about whether a file
    has changed, but also about whether it has changed more recently than
    some other file. But I'd think a simple version would useful to any
    network filesystem, or more generally to anything that caches a view of
    the filesystem either on another machine or in userspace.)

    > Feel free to show me, I seem to come up empty on using this value.

    Betraying my own interests--the NFSv4 protocol (unlike v2 or v3) uses a
    specialized "change" attribute to maintain cache consistency instead of
    depending on mtime/ctime. So nfsd would be one immediate in-kernel
    user. Currently we're using ctime, which causes obvious problems.

    But an improved ctime--one that actually increased whenever the file
    changed--would also do the job.

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