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    SubjectRe: [PATCH 00/32] VFS based Union Mount (V3)
    On Tue, Jun 09, 2009 at 12:44:06AM +0200, Jan Rekorajski wrote:
    > On Mon, 08 Jun 2009, Valerie Aurora wrote:
    >
    > > 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.
    >
    > As I don't need rw NFS, i didn't even try that :)
    >
    > > > 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.
    >
    > Thanks for clarification.
    >
    > > 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.
    >
    > I did just that, --union didn't change standard NFS behaviour.

    Er, excuse me - I mean to type "try it again WITHOUT the --union
    flag." My apologies!

    >
    > mount -t nfs server:/export/system /mnt
    > mount --union -t nfs server:/export/profile /mnt
    > mount.nfs: /mnt is busy or already mounted
    >
    > I did an experiment by using different IP of the server (same machine)
    > when mounting the second fs, mount worked then, but 'ls -1 /mnt' oopsed.
    > I can reproduce this and send you the oops next week.

    Interesting! Does this happen without the --union flag?

    -VAL


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