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    SubjectRe: NFS locking bug -- limited mtime resolution means nfs_lock() does not provide coherency guarantee
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    Theodore Y. Ts'o wrote:
    > Date: Thu, 14 Sep 2000 15:09:35 +0200 (CEST)
    > From: Trond Myklebust <trond.myklebust@fys.uio.no>
    >
    > Would it perhaps make sense to use one of these last 'free' fields
    > as a pointer to an 'inode entension'?
    > If you still want ext2fs to be able to accommodate new projects and
    > ideas, then it seems that being able to extend the inode is a
    > desirable feature, but perhaps this overlaps with the apparent plans
    > for adding resource forks?
    >
    > For stuff that's not commonly used, perhaps. The problem is that you
    > take a speed hit when you have to seek somewhere else to get at the
    > inode extension. So for something which is going to have to be
    > referenced for every stat() or getattr() operation, there are a real
    > performance issues with doing something like that.

    The "right" way to do this is to have a "this spot is in use, but you
    don't understand it" indication for an inode (*). The "expansion ptr"
    can then normally point to the directly following inode, but also
    somewhere completely different.

    So a "new" system would allocate a new inode in the directly following
    spot. But when a "new" system would need the extension part on an old
    filesystem, it would allocate the nearest inode and point the
    extension ptr there.

    Roger.


    (*) Actually the kernel only needs the "it's in use" part. fsck needs
    to know what it means or to properly ignore it....

    --
    ** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
    *-- BitWizard writes Linux device drivers for any device you may have! --*
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    ****** prejudices acquired by age eighteen. -- Albert Einstein ********
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