linux-kernel - Re: [Devel] Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

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Date:	Wed, 18 Apr 2007 11:19:46 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	linuxram@...ibm.com
CC:	serue@...ibm.com, devel@...nvz.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, viro@....linux.org.uk,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [Devel] Re: [patch 05/10] add "permit user mounts in new
	namespace" clone flag

> > Allowing this and other flags to NOT be propagated just makes it
> > possible to have a set of shared mounts with asymmetric properties,
> > which may actually be desirable.
> 
> The shared mount feature was designed to ensure that the mount remained
> identical at all the locations.

OK, so remount not propagating mount flags is a bug then?

> Now designing features to make it un-identical but still naming it
> shared, will break its original purpose.  Slave mounts were designed
> to make it asymmetric.

What if I want to modify flags in a master mount, but not the slave
mount?  Would I be screwed?  For example: mount is read-only in both
master and slave.  I want to mark it read-write in master but not in
slave.  What do I do?

> Whatever feature that is desired to be exploited; can that be exploited
> with the current set of semantics that we have? Is there a real need to
> make the mounts asymmetric but at the same time name them as shared?
> Maybe I dont understand what the desired application is? 

I do think this question of propagating mount flags is totally
independent of user mounts.

As it stands, currently remount doesn't propagate mount flags, and I
don't see any compelling reasons why it should.

The patchset introduces a new mount flag "allowusermnt", but I don't
see any compelling reason to propagate this flag _either_.

Please say so if you do have such a reason.  As I've explained, having
this flag set differently in parts of a propagation tree does not
interfere with or break propagation in any way.

Miklos

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