cgroups: net_cls as module

Allows the net_cls cgroup subsystem to be compiled as a module

This patch modifies net/sched/cls_cgroup.c to allow the net_cls subsystem
to be optionally compiled as a module instead of builtin.  The
cgroup_subsys struct is moved around a bit to allow the subsys_id to be
either declared as a compile-time constant by the cgroup_subsys.h include
in cgroup.h, or, if it's a module, initialized within the struct by
cgroup_load_subsys.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 31 insertions, 10 deletions

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 21f9c7678aa3..2f691fb180d1 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -328,13 +328,16 @@ config NET_CLS_FLOW
           module will be called cls_flow.
 
 config NET_CLS_CGROUP
-        bool "Control Group Classifier"
+        tristate "Control Group Classifier"
         select NET_CLS
         depends on CGROUPS
         ---help---
           Say Y here if you want to classify packets based on the control
           cgroup of their process.
 
+          To compile this code as a module, choose M here: the
+          module will be called cls_cgroup.
+
 config NET_EMATCH
         bool "Extended Matches"
         select NET_CLS
diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
index e4877ca6727c..7f27d2c15e08 100644
--- a/net/sched/cls_cgroup.c
+++ b/net/sched/cls_cgroup.c
@@ -24,6 +24,25 @@ struct cgroup_cls_state
         u32 classid;
 };
 
+static struct cgroup_subsys_state *cgrp_create(struct cgroup_subsys *ss,
+                                               struct cgroup *cgrp);
+static void cgrp_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp);
+static int cgrp_populate(struct cgroup_subsys *ss, struct cgroup *cgrp);
+
+struct cgroup_subsys net_cls_subsys = {
+        .name           = "net_cls",
+        .create         = cgrp_create,
+        .destroy        = cgrp_destroy,
+        .populate       = cgrp_populate,
+#ifdef CONFIG_NET_CLS_CGROUP
+        .subsys_id      = net_cls_subsys_id,
+#else
+#define net_cls_subsys_id net_cls_subsys.subsys_id
+#endif
+        .module         = THIS_MODULE,
+};
+
+
 static inline struct cgroup_cls_state *cgrp_cls_state(struct cgroup *cgrp)
 {
         return container_of(cgroup_subsys_state(cgrp, net_cls_subsys_id),
@@ -79,14 +98,6 @@ static int cgrp_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
         return cgroup_add_files(cgrp, ss, ss_files, ARRAY_SIZE(ss_files));
 }
 
-struct cgroup_subsys net_cls_subsys = {
-        .name           = "net_cls",
-        .create         = cgrp_create,
-        .destroy        = cgrp_destroy,
-        .populate       = cgrp_populate,
-        .subsys_id      = net_cls_subsys_id,
-};
-
 struct cls_cgroup_head
 {
         u32                     handle;
@@ -277,12 +288,19 @@ static struct tcf_proto_ops cls_cgroup_ops __read_mostly = {
 
 static int __init init_cgroup_cls(void)
 {
-        return register_tcf_proto_ops(&cls_cgroup_ops);
+        int ret = register_tcf_proto_ops(&cls_cgroup_ops);
+        if (ret)
+                return ret;
+        ret = cgroup_load_subsys(&net_cls_subsys);
+        if (ret)
+                unregister_tcf_proto_ops(&cls_cgroup_ops);
+        return ret;
 }
 
 static void __exit exit_cgroup_cls(void)
 {
         unregister_tcf_proto_ops(&cls_cgroup_ops);
+        cgroup_unload_subsys(&net_cls_subsys);
 }
 
 module_init(init_cgroup_cls);