ceph: document locking for ceph_set_dentry_offset

/*

 * Set dentry's directory position based on the current dir's max, and

 * order it in d_subdirs, so that dcache_readdir behaves.

 *

 * Always called under directory's i_mutex.

 */

static void ceph_set_dentry_offset(struct dentry *dn)

{

	struct dentry *dir = dn->d_parent;

	struct inode *inode = dn->d_parent->d_inode;

	struct inode *inode = dir->d_inode;

	struct ceph_dentry_info *di;

	BUG_ON(!inode);