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    SubjectRe: Versioning file system
    Bryan Henderson wrote:
    >> Part of the problem is that "whenever you modify a file"
    >> is ill-defined, or rather, if you were to take the literal meaning of it
    >> you'd end up with an unmanageable number of revisions.
    > Let me expand on that. Do you want to save a revision every time the user
    > types in an editor? Every time he runs a "save" command? Every time a
    > program does a write() system call? Every time a program closes a
    > modified file? If you're adding to a C program, is every draft you
    > compile a revision, or just the final modification after the bugs are
    > worked out?
    > When I was very new to coding, I used VMS and thought the automatic
    > revisioning would be a great thing because it would save me when I
    > modified a program and later regretted it. The system made a revision
    > every time I exited the editor. But I soon found that the "previous
    > revision" to which I wanted to revert was always many editings back, since
    > I spent a lot of time trying to make the regrettable code work before
    > giving up. VMS kept a fixed number of revisions per file. But keeping 20
    > versions of other files would have been wasteful of disk space, directory
    > listing space, etc.
    > Later, I discovered what I think are superior alternatives: RCS-style
    > version management on top of the filesystem, and automatic versioning
    > based on time instead of count of "modifications." For example, make a
    > copy of every changed file every hour and keep it for a day and keep one
    > of those for a week, and keep one of those for a month, etc. This works
    > even without snapshot technology and even without sub-file deltas. But of
    > course, it's better with those.

    From what I can see this seems to be the consesus (and it sound very
    sensible to me).

    The question remains is where to implement versioning: directly in
    individual filesystems or in the vfs code so all filesystems can use it?

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