linux-kernel - Re: RFC: permit link(2) to work across --bind mounts ?

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Message-ID: <Pine.LNX.4.64.0712290429350.29013@fbirervta.pbzchgretzou.qr>
Date:	Sat, 29 Dec 2007 04:31:28 +0100 (CET)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	dean gaudet <dean@...tic.org>
cc:	David Newall <david@...idnewall.com>, Mark Lord <lkml@....ca>,
	Al Viro <viro@....linux.org.uk>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: RFC: permit link(2)  to work across --bind mounts ?


On Dec 28 2007 18:53, dean gaudet wrote:
>p.s. in retrospect i probably could have arranged it more like this:
>
>  mount /dev/md1 $tmpmntpoint
>  mount --bind $tmpmntpoint/var /var
>  mount --bind $tmpmntpoint/home /home
>  umount $tmpmntpoint
>
>except i can't easily specify that in fstab... and neither of the bind 
>mounts would show up in df(1).  seems like it wouldn't be hard to support 
>this type of subtree mount though.  mount(8) could support a single 
>subtree mount using this technique but the second subtree mount attempt 
>would fail because you can't temporarily remount the device because the 
>mount point is gone.

Why is it gone?

mount /dev/md1 /tmpmnt
mount --bind /tmpmnt/var /var
mount --bind /tmpmnt/home /home

Is perfectly fine, and /tmpmnt is still alive and mounted. Additionally,
you can

umount /tmpmnt

now, which leaves only /var and /home.
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