From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCHv2 7/7] cgroup: mount cgroupns-root when inside non-init cgroupns Date: Mon, 3 Nov 2014 16:17:11 -0800 Message-ID: References: <1414783141-6947-1-git-send-email-adityakali@google.com> <1414783141-6947-8-git-send-email-adityakali@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Aditya Kali Cc: Linux API , Linux Containers , Serge Hallyn , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "Eric W. Biederman" , Tejun Heo , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Ingo Molnar List-Id: linux-api@vger.kernel.org On Mon, Nov 3, 2014 at 4:12 PM, Aditya Kali wrote: > On Mon, Nov 3, 2014 at 3:48 PM, Andy Lutomirski wrote: >> On Mon, Nov 3, 2014 at 3:23 PM, Aditya Kali wrote: >>> On Mon, Nov 3, 2014 at 3:15 PM, Andy Lutomirski wrote: >>>> On Mon, Nov 3, 2014 at 3:12 PM, Aditya Kali wrote: >>>>> On Fri, Oct 31, 2014 at 5:07 PM, Andy Lutomirski wrote: >>>>>> On Fri, Oct 31, 2014 at 12:19 PM, Aditya Kali wrote: >>>>>>> if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) { >>>>>>> pr_warn("sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n"); >>>>>>> - if (nr_opts != 1) { >>>>>>> + if (nr_opts > 1) { >>>>>>> pr_err("sane_behavior: no other mount options allowed\n"); >>>>>>> return -EINVAL; >>>>>> >>>>>> This looks wrong. But, if you make the change above, then it'll be right. >>>>>> >>>>> >>>>> It would have been nice if simple 'mount -t cgroup cgroup ' from >>>>> cgroupns does the right thing automatically. >>>>> >>>> >>>> This is a debatable point, but it's not what I meant. Won't your code >>>> let 'mount -t cgroup -o one_evil_flag cgroup mountpoint' through? >>>> >>> >>> I don't think so. This check "if (nr_opts > 1)" is nested under "if >>> (opts->flags & CGRP_ROOT_SANE_BEHAVIOR)". So we know that there is >>> atleast 1 option ('__DEVEL__sane_behavior') present (implicit or not). >>> Addition of 'one_evil_flag' will make nr_opts = 2 and result in EINVAL >>> here. >> >> But the implicit __DEVEL__sane_behavior doesn't increment nr_opts, right? >> > > Yes. Hence this change makes sure that we don't return EINVAL when > nr_opts == 0 or nr_opts == 1 :) > That way, both of the following are equivalent when inside non-init cgroupns: > > (1) $ mount -t cgroup -o __DEVEL__sane_behavior cgroup mountpoint > (2) $ mount -t cgroup cgroup mountpoint > > Any other mount option will trigger the error here. I still don't get it. Can you walk me through why mount -o some_other_option -t cgroup cgroup mountpoint causes -EINVAL? --Andy