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

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Message-Id: <201203251940.58668.a.miskiewicz@gmail.com>
Date:	Sun, 25 Mar 2012 19:40:58 +0200
From:	Arkadiusz Miśkiewicz <a.miskiewicz@...il.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	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 Sunday 25 of March 2012, Vasiliy Kulikov wrote:
> On Sun, Mar 25, 2012 at 09:24 +0200, Arkadiusz Miśkiewicz 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.
> 
> Procfs is a special filesystem.  Mount options are not reset on each
> mount(2) as you can mount procfs multiple times at different mount points
> (/proc/, /aaa/proc/, etc.).  Each time you add mount options they are
> applied to _each_ mount point because there is no per-mount point sb, but
> there is a per pid_ns superblock: pid_ns itself.  All options are stored
> at pid_ns.
> 
> When you mount it another time without any option nothing should change
> at the old mount points.  When you umount the last mount point all mount
> options are still stored.  When you mount it again old options are used
> (unless you override them).

I wonder if it should support noxx options then (like nogid, nohidepid) ? 

-- 
Arkadiusz Miśkiewicz        PLD/Linux Team
arekm / maven.pl            http://ftp.pld-linux.org/
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