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Date: Sun, 1 May 2005 06:15:27 -0400 (EDT)
From: Jeff Roberson <jroberson@chesapeake.net>
To: Oleg Sharoiko <os@rsu.ru>
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cc: freebsd-current@freebsd.org
cc: Kris Kennaway <kris@obsecurity.org>
Subject: Re: diskless/unionfs panics 
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On Sun, 1 May 2005, Oleg Sharoiko wrote:

>
> On Sun, 1 May 2005, Jeff Roberson wrote:
>
> JR>Where is this patch?
>
> It was quoted by Danny in his mail http://docs.freebsd.org/cgi/mid.cgi?E1DRs0M-0006E4-9a
> I sent it him privately, because I wasn't sure about the patch.

Yes, unfortunately this is only part of the problem.  The v_object can
change on a unionfs vnode leading to inconsistent results for mmap/exec.
This also causes problems for unionfs mounted on top of unionfs as the
lower vp can also change v_object fields.  This was one advantage to the
VOP based solution.  It would propagate all the way down the stack on each
access.

>
> Here it is:
> -----
> Index: union_vnops.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/fs/unionfs/union_vnops.c,v
> retrieving revision 1.131
> diff -u -r1.131 union_vnops.c
> --- union_vnops.c       13 Apr 2005 10:59:08 -0000      1.131
> +++ union_vnops.c       1 May 2005 07:50:27 -0000
> @@ -748,6 +748,9 @@
>         if (error == 0)
>                 error = VOP_OPEN(tvp, mode, cred, td, -1);
>
> +       if (error == 0)
> +               ap->a_vp->v_object = tvp->v_object;
> +
>         /*
>          * Release any locks held.
>          */
> -----
>
> I made it similar to the way it's done in nullfs. You can check my
> explanaitons quoted by Danny.
>
> --
> Oleg Sharoiko.
> Software and Network Engineer
> Computer Center of Rostov State University.
>