Subject: Re: /kern/kernel
To: None <>
From: Greg A. Woods <>
List: current-users
Date: 09/14/1998 15:25:37
[ On Mon, September 14, 1998 at 08:23:55 (-0400), der Mouse wrote: ]
> Subject: Re: /kern/kernel
> The problem is, / is mounted read-only.  To remount it read-write,
> userland does "mount -o update /dev/whatever /".  This doesn't work,
> because when the kernel looks up / to get the mounted-on vnode, it gets
> a different vnode from the one the root device is currently mounted on.
> I'm thinking about possible ways to fix this, but so far all I have is
> ideas.  (The one I currently favor is to remember the *real* root and
> have mount(2) silently substitute that when userland tries to mount
> onto rootvnode.  Note this doesn't affect how mount(2) interacts with
> chroot(2), because I'm talking about rootvnode, not fd_rdir.)

I believe this is why SCO Xenix (and possibly other implementations)
have a /dev/root and /dev/rroot.  These are virtual devices that always
point at the "real" one -- i.e. the one set at boot time either because
that's where the kernel was loaded from, or that's where the user
specified for the equivalent of a "boot -a".  That way "mount -o
update,rw /dev/root /" is always correct.  Although if I remember right
finding out what the real root disk is from user-land is left as an
exercise to the user.....

							Greg A. Woods

+1 416 218-0098      VE3TCP      <>      <robohack!woods>
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