Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751301AbaKDAuG (ORCPT <rfc822;w@1wt.eu>);
	Mon, 3 Nov 2014 19:50:06 -0500
Received: from mail-ob0-f176.google.com ([209.85.214.176]:43268 "EHLO
	mail-ob0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750905AbaKDAuD (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 3 Nov 2014 19:50:03 -0500
MIME-Version: 1.0
In-Reply-To: <CALCETrXeG2t=fW9HbkirDZudw9pbDwoqDq5ygJBkBMbqqoDAvw@mail.gmail.com>
References: <1414783141-6947-1-git-send-email-adityakali@google.com>
 <1414783141-6947-8-git-send-email-adityakali@google.com> <CALCETrXTaZ3SJ_t-gnbc93BVZXg-912NqO78kFd0Tpi-5-dZoQ@mail.gmail.com>
 <CAGr1F2FuPQxLraYv7PstJ9c8H-XQsgawaAtj4AS77B+_0k2o+A@mail.gmail.com>
 <CALCETrW64-6xC6psP-8k0H-1GfVnWBTeEBNSrE_sH+-DFtuZQQ@mail.gmail.com>
 <CAGr1F2GX45gC-V7kEzVjp-EiYfdPDVBRs+99nASpgFVAdYX+1w@mail.gmail.com>
 <CALCETrUB_xx5zno26k5UjAFt77nZTpgyndD4AuBSZxiZBNjXSw@mail.gmail.com>
 <CAGr1F2EV4p_nJP_oMe3N8pBPedAZHbdB=XCMPjSEZTC9jmZoAg@mail.gmail.com> <CALCETrXeG2t=fW9HbkirDZudw9pbDwoqDq5ygJBkBMbqqoDAvw@mail.gmail.com>
From: Aditya Kali <adityakali@google.com>
Date: Mon, 3 Nov 2014 16:49:41 -0800
Message-ID: <CAGr1F2Ecd3vCkDHVpFevZDLt+J49MimYh0va9u7JEJVTLHq8uQ@mail.gmail.com>
Subject: Re: [PATCHv2 7/7] cgroup: mount cgroupns-root when inside non-init cgroupns
To: Andy Lutomirski <luto@amacapital.net>
Cc: Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Serge Hallyn <serge.hallyn@ubuntu.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>, cgroups@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Linux Containers <containers@lists.linux-foundation.org>,
        Rohit Jnagal <jnagal@google.com>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 3, 2014 at 4:17 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Mon, Nov 3, 2014 at 4:12 PM, Aditya Kali <adityakali@google.com> wrote:
>> On Mon, Nov 3, 2014 at 3:48 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>> On Mon, Nov 3, 2014 at 3:23 PM, Aditya Kali <adityakali@google.com> wrote:
>>>> On Mon, Nov 3, 2014 at 3:15 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>>> On Mon, Nov 3, 2014 at 3:12 PM, Aditya Kali <adityakali@google.com> wrote:
>>>>>> On Fri, Oct 31, 2014 at 5:07 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>>>>>>> On Fri, Oct 31, 2014 at 12:19 PM, Aditya Kali <adityakali@google.com> 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 <mnt>' 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?
>

Argh! You are right. I was totally convinced that this works. But it
clearly doesn't if you specify 1 legit mount option. I wanted to make
it work for both cases (1) and (2) above. But then this check will
have to be changed :(
Sorry about the back and forth. I am just going to make it return
EINVAL if __DEVEL_sane_behavior is not specified as suggested in the
beginning.

> --Andy

-- 
Aditya
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/