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Date: Sun, 14 Oct 2001 13:32:31 -0400 (EDT)
From: Alexander Viro <viro@math.psu.edu>
To: Ville Herva <vherva@mail.niksula.cs.hut.fi>
cc: linux-kernel@vger.kernel.org
Subject: Re: mount --bind and -o [re: nosuid/noexec/nodev handling]
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On Sun, 14 Oct 2001, Ville Herva wrote:

> $?mount --bind -o ro /mnt/ext2-2 /tmp/test

i.e.
mount --bind /mnt/ext2-2 /tmp/test

> $?mount --bind -o remount,ro  /tmp/test           

i.e.
mount -o remount,ro /tmp/test

> $ mount
> (...)
> /dev/hde1 on /mnt/ext2-2 type reiserfs (rw,noatime,nodiratime)
> /mnt/ext2-2 on /tmp/test type none (ro,bind)

Confused mount(8) - apparently uses /etc/mtab and doesn't manage to deduce
the changes done by remounting (/etc/mtab is maintained by userland;
/proc/mounts is handled by kernel and is supposed to be accurate).

> $ touch /mnt/ext2-2/a
> touch: /mnt/ext2-2/a: Read-only file system

Sure, read-only is per-superblock right now.  Change it on one instance
and you've changed it on all of them.

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