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

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Message-ID: <Pine.LNX.4.64.0712290747260.23321@fbirervta.pbzchgretzou.qr>
Date:	Sat, 29 Dec 2007 07:48:25 +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 22:02, dean gaudet wrote:
>
>i was trying to come up with a userland-only change in mount(8) which
>would behave like so:
>
># mount --subtree var /dev/md1 /var
>  internally mount does:
>  - mount /dev/md1 /tmpmnt
>  - mount --bind /tmpmnt/var /var
>  - umount /tmpmnt
>
># mount --subtree home /dev/md1 /home
>  internally mount does:
>  - mount /dev/md1 /tmpmnt
>  - mount --bind /tmpmnt/home /home
>  - umount /tmpmnt
>
>but that second mount would fail because /dev/md1 is already mounted
>(but the mount point is gone)...

I do not think it would fail. Like this:

# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/home     208486056 158605472  49880584  77% /home
# mount /dev/mapper/home /mnt
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/home     208486056 158605472  49880584  77% /home
/dev/mapper/home     208486056 158605472  49880584  77% /mnt

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