Support Directory Creation

When we instantiated the root-inode, we attached an inode-operations object - struct stamfs_dir_iops. It has a "mkdir" entry - to which we now attach stamfs_iop_mkdir():

• Allocate a new inode for the child (see next slide).
• Turn this inode into an empty-directory inode.
• Increase the parent's link-count (the child's ".." points to the parent).
• Increase the child's link-count (the child's "." points back at the child).
• Add the child to the list of children of the parent.
• Instantiate the child's dentry.

Originally written by guy keren