linux-kernel - Re: Removing shared subtrees?

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Message-ID: <20140930000924.GO7996@ZenIV.linux.org.uk>
Date:	Tue, 30 Sep 2014 01:09:24 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: Removing shared subtrees?

On Mon, Sep 29, 2014 at 04:45:42PM -0700, Andy Lutomirski wrote:
> As far as I know, shared subtrees in recursive bind mounts are a
> misfeature that existed for the sole purpose of allowing recursive
> binds + chroot to emulate mount namespaces.

Wrong.  Different namespaces vs. multiple mounts in the same namespace
have nothing whatsoever with shared vs. slave.  It's completely orthogonal.

>  But we have mount
> namespaces, so what are they for?

???

> They're totally fsked up.  For example, don't try this on a live system:
> 
> # mount --make-rshared /
> # mount --rbind / /mnt
> # umount -l /mnt
> 
> It will unmount *everything*.

So will umount -l /

>  On Fedora, you don't even need the
> --make-rshared part.  WTF?

"Doctor, it hurts when I do it..."

I can suggest a few more self-LARTs, if you are interested...

> Can we just remove the feature entirely in linux-next and see if
> anyone complains?  I'm all for propagation across mount namespaces,
> but I suspect that, at the very least, there is no legitimate reason
> whatsoever for mounts to propagate from a recursive bind mount back to
> the origin.
> 
> IOW, can we kill shared mounts and just keep private and slave mounts?

What for?
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