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    SubjectRe: [PATCH 00/32] VFS based Union Mount (V3)
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    On Tue, 19 May 2009, Jan Blunck wrote:
    > The directory in the topmost filesystem is created during
    > lookup. The contents of the directory isn't copied up presistently
    > at that point in time. Therefore you have an empty directory in the
    > topmost filesystem after the lookup. This was necessary to get rid
    > of the union_relookup_topmost() calls during create, mknod, mkdir
    > etc.
    >
    > When readdir is called, the topmost directory is filed up with
    > fallthru entries which are persistently stored. This is only
    > necessary to get readdir right wrt POSIX. During lookup the fallthru
    > dentry, which is in fact a special negative dentry, is ignored and
    > therefore the lookup continues on the lower filesystem.

    So this means that the topmost branch always needs to be writable,
    right? It isn't possible to make a union of two iso9660 filesystems,
    for example?

    Thanks,
    Miklos


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