[PATCH 1/5] cgroup, blkcg: Prepare some symbols for module and !CONFIG_CGROUP usages

[Tejun Heo]

btrfs is going to use css_put() and wbc helpers to improve cgroup
writeback support.  Add dummy css_get() definition and export wbc
helpers to prepare for module and !CONFIG_CGROUP builds.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
 block/blk-cgroup.c     | 1 +
 fs/fs-writeback.c      | 3 +++
 include/linux/cgroup.h | 1 +
 3 files changed, 5 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 53b7bd4c7000..3319ab4ff262 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -47,6 +47,7 @@ struct blkcg blkcg_root;
 EXPORT_SYMBOL_GPL(blkcg_root);
 
 struct cgroup_subsys_state * const blkcg_root_css = &blkcg_root.css;
+EXPORT_SYMBOL_GPL(blkcg_root_css);
 
 static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];
 
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 9ebfb1b28430..a8a40bc26c2f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -270,6 +270,7 @@ void __inode_attach_wb(struct inode *inode, struct page *page)
 	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
 		wb_put(wb);
 }
+EXPORT_SYMBOL_GPL(__inode_attach_wb);
 
 /**
  * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
@@ -582,6 +583,7 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
 	if (unlikely(wb_dying(wbc->wb)))
 		inode_switch_wbs(inode, wbc->wb_id);
 }
+EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
 
 /**
  * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
@@ -701,6 +703,7 @@ void wbc_detach_inode(struct writeback_control *wbc)
 	wb_put(wbc->wb);
 	wbc->wb = NULL;
 }
+EXPORT_SYMBOL_GPL(wbc_detach_inode);
 
 /**
  * wbc_account_io - account IO issued during writeback
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c0077adeea83..da9d2afbcf0c 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -687,6 +687,7 @@ void cgroup_path_from_kernfs_id(const union kernfs_node_id *id,
 struct cgroup_subsys_state;
 struct cgroup;
 
+static inline void css_get(struct cgroup_subsys_state *css) {}
 static inline void css_put(struct cgroup_subsys_state *css) {}
 static inline int cgroup_attach_task_all(struct task_struct *from,
 					 struct task_struct *t) { return 0; }
-- 
2.17.1