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    SubjectRe: [PATCHv2 7/7] cgroup: mount cgroupns-root when inside non-init cgroupns
    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.


    > --Andy

    --
    Aditya


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