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    SubjectRe: [PATCH 00/32] VFS based Union Mount (V3)
    On Thu, May 21, 2009 at 02:54:19PM +0200, Jan Rekorajski wrote:
    > On Mon, 18 May 2009, Jan Blunck wrote:
    >
    > > Here is another post of the VFS based union mount implementation.
    >
    > Is there any chance this will support NFS? I can union-mount tmpfs over

    NFS as the read-only layer ought to work. NFS as the read-write layer
    is still up in the air.

    > nfs mounted fs, but if I try to mount --union two NFS filesystems I
    > always get -EBUSY on second mount on the same mountpoint.
    >
    > Something along these lines:
    >
    > doesn't matter if I use --union on first mount, the result is always the
    > same.
    >
    > mount <--union> -t nfs server:/export/system /mnt
    > OK
    > mount --union -t nfs server:/export/profile /mnt
    > mount.nfs: /mnt is busy or already mounted
    >
    > I patched mount.nfs so it knows about MS_UNION, and strace shows me that
    > it passes that flag to kernel.

    FYI, using --union on the first mount will make it union with the
    local directory below it. The --union option is not needed when you
    mount the lower read-only layer.

    You'll get -EBUSY on the second mount of any NFS file system over
    another - try it again with the --union flag. Support for NFS on NFS
    union mount would have to change this.

    -VAL


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