• Tejun Heo's avatar
    cgroup: add css_parent() · 63876986
    Tejun Heo authored
    Currently, controllers have to explicitly follow the cgroup hierarchy
    to find the parent of a given css.  cgroup is moving towards using
    cgroup_subsys_state as the main controller interface construct, so
    let's provide a way to climb the hierarchy using just csses.
    This patch implements css_parent() which, given a css, returns its
    parent.  The function is guarnateed to valid non-NULL parent css as
    long as the target css is not at the top of the hierarchy.
    freezer, cpuset, cpu, cpuacct, hugetlb, memory, net_cls and devices
    are converted to use css_parent() instead of accessing cgroup->parent
    * __parent_ca() is dropped from cpuacct and its usage is replaced with
      parent_ca().  The only difference between the two was NULL test on
      cgroup->parent which is now embedded in css_parent() making the
      distinction moot.  Note that eventually a css->parent field will be
      added to css and the NULL check in css_parent() will go away.
    This patch shouldn't cause any behavior differences.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: default avatarLi Zefan <lizefan@huawei.com>