This works on obviating the need for a separate data type to describe a sysfs
directory (which was renamed from struct driver_dir_entry to struct sysfs_dir).

All sysfs creation and removal functions now take a struct kobject, instead
of a struct sysfs_dir. This kobject is embedded in ->d_fsdata of the directory.

sysfs_create_dir() takes only 1 parameter now: the object that we're creating
the directory for. The parent dentry is derived by looking at the object's 
parent. 

sysfs_create_file() takes the object as the first parameter, and the attribute
as the second, which makes more sense from an API perspective. 

sysfs_remove_file() now takes an attribute as a second parameter, to be 
consistent with the creation function.

sysfs_remove_link() is created, which is basically the old sysfs_remove_file().
(symlinks don't have an attribute associated with them; only a name, which was
prohibiting the previous change). 

open() and close() look for a kobject now, and do refcounting directly on the
object. Because of that, we don't need the ->open() and ->close() callbacks
in struct sysfs_ops, so they've been removed. 

read() and write() also now look for a kobject now. 

The comments have been updated, too.