Re: [PATCH net-next v4 2/3] bpf: Add bpf_current_task_under_cgroup helper

[Sargun Dhillon <sargun@sargun.me>]

On Fri, Aug 12, 2016 at 09:16:07AM +0200, Daniel Borkmann wrote:
> On 08/12/2016 06:50 AM, Sargun Dhillon wrote:
> >I realize that in_cgroup is more consistent, but under_cgroup makes
> >far more sense to me. I think it's more intuitive.
> >
> >On Thu, Aug 11, 2016 at 9:48 PM, Alexei Starovoitov
> ><alexei.starovoitov@gmail.com> wrote:
> >>On Thu, Aug 11, 2016 at 08:14:56PM -0700, Sargun Dhillon wrote:
> >>>This adds a bpf helper that's similar to the skb_in_cgroup helper to check
> >>>whether the probe is currently executing in the context of a specific
> >>>subset of the cgroupsv2 hierarchy. It does this based on membership test
> >>>for a cgroup arraymap. It is invalid to call this in an interrupt, and
> >>>it'll return an error. The helper is primarily to be used in debugging
> >>>activities for containers, where you may have multiple programs running in
> >>>a given top-level "container".
> >>>
> >>>Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> >>>Cc: Alexei Starovoitov <ast@kernel.org>
> >>>Cc: Daniel Borkmann <daniel@iogearbox.net>
> >>>Cc: Tejun Heo <tj@kernel.org>
> >>>---
> >>>+     /**
> >>>+      * bpf_current_task_under_cgroup(map, index) - Check cgroup2 membership of current task
> >>>+      * @map: pointer to bpf_map in BPF_MAP_TYPE_CGROUP_ARRAY type
> >>>+      * @index: index of the cgroup in the bpf_map
> >>>+      * Return:
> >>>+      *   == 0 current failed the cgroup2 descendant test
> >>>+      *   == 1 current succeeded the cgroup2 descendant test
> >>>+      *    < 0 error
> >>>+      */
> >>>+     BPF_FUNC_current_task_under_cgroup,
> >>..
> >>>       case BPF_MAP_TYPE_CGROUP_ARRAY:
> >>>-             if (func_id != BPF_FUNC_skb_in_cgroup)
> >>>+             if (func_id != BPF_FUNC_skb_in_cgroup &&
> >>>+                 func_id != BPF_FUNC_current_task_under_cgroup)
> >>>                       goto error;
> >>...
> >>>+     case BPF_FUNC_current_task_under_cgroup:
> >>>       case BPF_FUNC_skb_in_cgroup:
> >>
> >>Tejun,
> >>do you feel strongly about 'under' ?
> >>It just looks inconsistent vs existing skb_in_cgroup...
> >>"in cgroup" - 4k google hits
> >>"under cgroup" - 2k google hits
> 
> Alternative could be that we take "BPF_FUNC_current_in_cgroup" as a
> helper enum to keep consistency with what we have wrt skb helper, but
> for the cgroup header have the suggested task_under_cgroup_hierarchy()
> name.

I actually wish we could rename skb_in_cgroup to skb_under_cgroup. If we ever 
introduced a check for absolute membership versus ancestral membership, what 
would we call that?