kernfs: introduce kernfs_node_id

inode number and generation can identify a kernfs node. We are going to
export the identification by exportfs operations, so put ino and
generation into a separate structure. It's convenient when later patches
use the identification.

Acked-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Shaohua Li <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/kernfs/dir.c

···
 	}
 	kfree(kn->iattr);
 	spin_lock(&kernfs_idr_lock);
-	idr_remove(&root->ino_idr, kn->ino);
+	idr_remove(&root->ino_idr, kn->id.ino);
 	spin_unlock(&kernfs_idr_lock);
 	kmem_cache_free(kernfs_node_cache, kn);
 
···
 	idr_preload_end();
 	if (ret < 0)
 		goto err_out2;
-	kn->ino = ret;
-	kn->generation = gen;
+	kn->id.ino = ret;
+	kn->id.generation = gen;
 
 	/*
 	 * set ino first. This barrier is paired with atomic_inc_not_zero in
···
 	 * before 'count'. So if 'count' is uptodate, 'ino' should be uptodate,
 	 * hence we can use 'ino' to filter stale node.
 	 */
-	if (kn->ino != ino)
+	if (kn->id.ino != ino)
 		goto out;
 	rcu_read_unlock();
 
···
 		const char *name = pos->name;
 		unsigned int type = dt_type(pos);
 		int len = strlen(name);
-		ino_t ino = pos->ino;
+		ino_t ino = pos->id.ino;
 
 		ctx->pos = pos->hash;
 		file->private_data = pos;

fs/kernfs/file.c

···
 		 * have the matching @file available.  Look up the inodes
 		 * and generate the events manually.
 		 */
-		inode = ilookup(info->sb, kn->ino);
+		inode = ilookup(info->sb, kn->id.ino);
 		if (!inode)
 			continue;
 
···
 		if (parent) {
 			struct inode *p_inode;
 
-			p_inode = ilookup(info->sb, parent->ino);
+			p_inode = ilookup(info->sb, parent->id.ino);
 			if (p_inode) {
 				fsnotify(p_inode, FS_MODIFY | FS_EVENT_ON_CHILD,
 					 inode, FSNOTIFY_EVENT_INODE, kn->name, 0);

fs/kernfs/inode.c

···
 	inode->i_private = kn;
 	inode->i_mapping->a_ops = &kernfs_aops;
 	inode->i_op = &kernfs_iops;
-	inode->i_generation = kn->generation;
+	inode->i_generation = kn->id.generation;
 
 	set_default_inode_attr(inode, kn->mode);
 	kernfs_refresh_inode(kn, inode);
···
 {
 	struct inode *inode;
 
-	inode = iget_locked(sb, kn->ino);
+	inode = iget_locked(sb, kn->id.ino);
 	if (inode && (inode->i_state & I_NEW))
 		kernfs_init_inode(kn, inode);
 

include/linux/cgroup.h

···
 /* returns ino associated with a cgroup */
 static inline ino_t cgroup_ino(struct cgroup *cgrp)
 {
-	return cgrp->kn->ino;
+	return cgrp->kn->id.ino;
 }
 
 /* cft/css accessors for cftype->write() operation */

include/linux/kernfs.h

···
 	struct kernfs_node	*notify_next;	/* for kernfs_notify() */
 };
 
+/* represent a kernfs node */
+union kernfs_node_id {
+	struct {
+		u32		ino;
+		u32		generation;
+	};
+	u64			id;
+};
+
 /*
  * kernfs_node - the building block of kernfs hierarchy.  Each and every
  * kernfs node is represented by single kernfs_node.  Most fields are
···
 
 	void			*priv;
 
+	union kernfs_node_id	id;
 	unsigned short		flags;
 	umode_t			mode;
-	unsigned int		ino;
 	struct kernfs_iattrs	*iattr;
-	u32			generation;
 };
 
 /*

include/trace/events/writeback.h

···
 
 static inline unsigned int __trace_wb_assign_cgroup(struct bdi_writeback *wb)
 {
-	return wb->memcg_css->cgroup->kn->ino;
+	return wb->memcg_css->cgroup->kn->id.ino;
 }
 
 static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *wbc)