linux-kernel - Re: [PATCH] proc: fix mount -t proc -o AAA

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Message-ID: <97428.1332714196@turing-police.cc.vt.edu>
Date:	Sun, 25 Mar 2012 18:23:16 -0400
From:	Valdis.Kletnieks@...edu
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Arkadiusz Miśkiewicz <a.miskiewicz@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH] proc: fix mount -t proc -o AAA

On Sun, 25 Mar 2012 19:36:12 +0400, Vasiliy Kulikov said:
> On Sun, Mar 25, 2012 at 09:24 +0200, Arkadiusz Mi��kiewicz wrote:
> > but there is another problem - unmounting it and mounting without options
> > causes old option to persist:
> >
> > # mount none /proc -t proc -o hidepid=2
> > # umount /proc
> > # mount none /proc -t proc
> > # grep "/proc" /proc/mounts
> > none /proc proc rw,relatime,hidepid=2 0 0
> >
> > There should be no hidepid=2 now.
>
> No, that's an expected behaviour.

"You keep using that word. I do not think it means what you think it means". ;)

> Procfs is a special filesystem.

And the fact it's "special" makes this *unexpected* behavior.  Are there
any other filesystems where -o values will persist across an unmount
and then take effect *even if no -o is given* on a subsequent mount?

Yes, it may be what the code actually *does*, but it certainly violates
the Principle of Least Surprise...

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