From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Serge E. Hallyn" Subject: Re: [PATCH v1 3/3] cgroup: relax common ancestor restriction for direct descendants Date: Thu, 21 Jul 2016 09:33:30 -0500 Message-ID: <20160721143330.GA5751@mail.hallyn.com> References: <20160718161816.13040-1-asarai@suse.de> <20160718161816.13040-4-asarai@suse.de> <20160720155147.GG4574@htj.duckdns.org> <6e975d80-4077-fb8b-ec84-708e37c8e149@suse.de> <20160720230228.GA19588@mtj.duckdns.org> <982fcf3a-3685-9bd7-dd95-7bff255c9421@suse.de> <20160720231949.GB19588@mtj.duckdns.org> <379e5b13-29d4-ca75-1935-0a64f3db8d27@suse.de> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <379e5b13-29d4-ca75-1935-0a64f3db8d27-l3A5Bk7waGM@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Aleksa Sarai Cc: Tejun Heo , Greg Kroah-Hartman , Li Zefan , Johannes Weiner , "Serge E. Hallyn" , Aditya Kali , Chris Wilson , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christian Brauner , dev-IGmTWi+3HBZvNhPySn5qfx2eb7JE58TQ@public.gmane.org, James Bottomley Quoting Aleksa Sarai (asarai-l3A5Bk7waGM@public.gmane.org): > >>I feel like the permission model makes sense in certain cases (the common > >>ancestor restriction, as well as the ability for a parent to apply limits to > >>children by setting its own limits). Neither of those are violated (if you > >>read the commit that introduced the common ancestor restriction). > >> > >>Maybe if you give me a usecase of when it might be important that a process > >>must not be able to move to a sub-cgroup of its current one, I might be able > >>to understand your concerns? From my perspective, I think that's actually > >>quite useful. > > > >cgroup is used to keep track of which processes belong where and > >allowing processes to be moved out of its cgroup like this would be > >surprising to say the least. > > Would you find it acceptable if we added a bit that would make this > not happen (you could specify that a cgroup should not allow a > process to move itself to a sub-cgroup)? Or an aggregate > cgroup.procs that gives you all of the processes in the entire > branch of the tree? Surely this is something that can be fixed > without unnecessarily restricting users from doing useful things. > > >>The reason I'm doing this is so that we might be able to _practically_ use > >>cgroups as an unprivileged user (something that will almost certainly be > >>useful to not just the container crowd, but people also planning on using > >>cgroups as advanced forms of rlimits). > > > >I don't get why we need this fragile dance with permissions at all > >when the same functionality can be achieved by delegating explicitly. > > The key words being "unprivileged user". Currently, if I am a > regular user on a system and I want to use the freezer cgroup to > pause a process I am running, I have to *go to the administrator and > ask them to give me permission to do that*. Why is that necessary? I Ths is of course solvable using something like libpam-cgfs or libpam-cgm (and others). Since this sounds like a question of policy, not mechanism, userspace seems like the right place. Is there a downside to that (or, as Tejun put it, "delegating explicitly")?