cgroup: use bitmask to filter for_each_subsys
Add a new macro for_each_subsys_which that allows all enabled cgroup
subsystems to be filtered by a bitmask, such that mask & (1 << ssid)
determines if the subsystem is to be processed in the loop body (where
ssid is the unique id of the subsystem).
Also replace the need_forkexit_callback with two separate bitmasks for
each callback to make (ss->{fork,exit}) checks unnecessary.
tj: add a short comment for "if (!CGROUP_SUBSYS_COUNT)".
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 26d1cea..c5588c4 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -490,6 +490,8 @@
#else /* CONFIG_CGROUPS */
+#define CGROUP_SUBSYS_COUNT 0
+
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {}
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}