linux-kernel - Re: [PATCH] Send quota messages via netlink

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Message-ID: <20070830092548.GB16336@duck.suse.cz>
Date:	Thu, 30 Aug 2007 11:25:48 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Balbir Singh <balbir@...ibm.com>,
	"Serge E. Hallyn" <serue@...ibm.com>, containers@...ts.osdl.org
Subject: Re: [PATCH] Send quota messages via netlink

On Wed 29-08-07 15:06:43, Eric W. Biederman wrote:
> Jan Kara <jack@...e.cz> writes:
> >> However I'm still confused about the use of current->user.  If that
> >> is what we really want and not the user who's quota will be charged
> >> it gets to be a really trick business, because potentially the uid
> >> we want to deliver varies depending on who opened the netlink socket.
> >   I see it's a complicated matter :). What I need to somehow pass to
> > userspace is something (and I don't really care whether it will be number,
> > string or whatever) that userspace can read and e.g. find a terminal
> > window or desktop the affected user has open and also translate the
> > identity to some user-understandable name (average user Joe has to
> > understand that he should quickly cleanup his home directory ;).
> >   Thinking more about it, we could probably pass a string to userspace in
> > the format:
> >   <namespace type>:<user identification>
> >
> > So for example we can have something like:
> >   unix:1000 (traditional unix UIDs)
> >   nfs4:joe@...hine
> >
> > The problem is: Are we able to find out in which "namespace type" we are
> > and send enough identifying information from a context of unpriviledged
> > user?
> 
> Ok.  This provides enough context to understand what you are trying to do.
> You do want the unix user id, not the filesystem notion.  Because you
> are looking for the user.
> 
> So we have to figure out how to do the hard thing which is look at
> who opened our netlink broadcast see if they are in the same user
> namespace as current->user.  Which is a pain and we don't currently
> have the infrastructure for.
  There can be arbitrary number of listeners (potentially from different
namespaces if I understand it correctly) listening to broadcasts. So I
think we should pass some universal identifier rather than try to find out
who is listening etc. I think such identifiers would be useful for other
things too, won't they?
  BTW: Do you have some idea, when would be the infrastructure clearer?
Whether it makes sence to currently proceed with UIDs and later change it
to something generic or whether I should wait before you sort it out :).

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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