btrfs: constify tracepoint arguments

Tracepoint arguments are all read-only.  If we mark the arguments
as const, we're able to keep or convert those arguments to const
where appropriate.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/async-thread.c

@@ -75,18 +75,18 @@ void btrfs_##name(struct work_struct *arg)				\
 }
 
 struct btrfs_fs_info *
-btrfs_workqueue_owner(struct __btrfs_workqueue *wq)
+btrfs_workqueue_owner(const struct __btrfs_workqueue *wq)
 {
 	return wq->fs_info;
 }
 
 struct btrfs_fs_info *
-btrfs_work_owner(struct btrfs_work *work)
+btrfs_work_owner(const struct btrfs_work *work)
 {
 	return work->wq->fs_info;
 }
 
-bool btrfs_workqueue_normal_congested(struct btrfs_workqueue *wq)
+bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq)
 {
 	/*
 	 * We could compare wq->normal->pending with num_online_cpus()

fs/btrfs/async-thread.h

@@ -82,7 +82,7 @@ void btrfs_queue_work(struct btrfs_workqueue *wq,
 void btrfs_destroy_workqueue(struct btrfs_workqueue *wq);
 void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max);
 void btrfs_set_work_high_priority(struct btrfs_work *work);
-struct btrfs_fs_info *btrfs_work_owner(struct btrfs_work *work);
-struct btrfs_fs_info *btrfs_workqueue_owner(struct __btrfs_workqueue *wq);
-bool btrfs_workqueue_normal_congested(struct btrfs_workqueue *wq);
+struct btrfs_fs_info *btrfs_work_owner(const struct btrfs_work *work);
+struct btrfs_fs_info *btrfs_workqueue_owner(const struct __btrfs_workqueue *wq);
+bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq);
 #endif

fs/btrfs/btrfs_inode.h

@@ -207,7 +207,7 @@ struct btrfs_inode {
 
 extern unsigned char btrfs_filetype_table[];
 
-static inline struct btrfs_inode *BTRFS_I(struct inode *inode)
+static inline struct btrfs_inode *BTRFS_I(const struct inode *inode)
 {
 	return container_of(inode, struct btrfs_inode, vfs_inode);
 }
@@ -231,7 +231,7 @@ static inline void btrfs_insert_inode_hash(struct inode *inode)
 	__insert_inode_hash(inode, h);
 }
 
-static inline u64 btrfs_ino(struct btrfs_inode *inode)
+static inline u64 btrfs_ino(const struct btrfs_inode *inode)
 {
 	u64 ino = inode->location.objectid;