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    SubjectRe: fsync on large files
    Alexander Viro <> wrote:
    > OK, so you are doing lookup on foo from /bar/baz. You see that foo is a
    > directory and it has another parent. You see that this parent is nowhere
    > near dcache/icache. Worse yet, actually it's the end of *long* chain of
    > directories and none of them (except the root, that is) is in dcache. To
    > make it even nastier, suppose that there are fan-ins in that chain (i.e
    > some of those directories also have multiple parents). Your actions?

    Bring at least one instance of each parent into dcache. I don't think
    this should be significantly worse than having a long path for the first
    reference to a directory.

    I haven't thought a lot about tricks with mount (union filesystems, etc.)
    but I'm assuming that we're not going to allow stunts like mounting a
    file system in a subdirectory contained inside itself. So, you don't
    have to worry once you cross the mount point, even if the mount point
    has multiple identities -- hard links can't span filesystems.

    Note that I'm presuming that, within the filesystem, each directory must
    have an internal unique id (perhaps block # -- if the file system doesn't
    have inodes), and that the test you want to perform is: directory being
    renamed is not in the set of {target directory, ancestors of target
    directory in this same filesystem}.

    > Now, assume that another lookup goes through the alternative path in the
    > same time from the other direction. Your actions wrt locking?

    Use a per-filesystem directory rename lock when renaming a directory
    and parallel parents are an issue. [I guess, to be safe, we'd have to
    use the lock to determine if parallel parents are an issue.]


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