On Sun, May 13, 2018 at 07:33:18PM +0200, Alban Crequy wrote:

 
+BPF_CALL_2(bpf_get_current_cgroup_ino, u32, hierarchy, u64, flags)
+{
+	// TODO: pick the correct hierarchy instead of the mem controller
+	struct cgroup *cgrp = task_cgroup(current, memory_cgrp_id);
+
+	if (unlikely(!cgrp))
+		return -EINVAL;
+	if (unlikely(hierarchy))
+		return -EINVAL;
+	if (unlikely(flags))
+		return -EINVAL;
+
+	return cgrp->kn->id.ino;

ino only is not enough to identify cgroup. It needs generation number too.
I don't quite see how hierarchy and flags can be used in the future.
Also why limit it to memcg?

How about something like this instead:

BPF_CALL_2(bpf_get_current_cgroup_id)
{
        struct cgroup *cgrp = task_dfl_cgroup(current);

        return cgrp->kn->id.id;
}
The user space can use fhandle api to get the same 64-bit id.