Get upper or lower inode we should be using
struct inode * d_backing_inode(const struct dentry * upper);
upper
The upper layer
This is the helper that should be used to get at the inode that will be used if this dentry were to be opened as a file. The inode may be on the upper dentry or it may be on a lower dentry pinned by the upper.
Normal filesystems should not use this to access their own inodes.