configfs: Allow ->make_item() and ->make_group() to return detailed errors.
The configfs operations ->make_item() and ->make_group() currently return a new item/group. A return of NULL signifies an error. Because of this, -ENOMEM is the only return code bubbled up the stack. Multiple folks have requested the ability to return specific error codes when these operations fail. This patch adds that ability by changing the ->make_item/group() ops to return ERR_PTR() values. These errors are bubbled up appropriately. NULL returns are changed to -ENOMEM for compatibility. Also updated are the in-kernel users of configfs. This is a rework of reverted commit 11c3b792 . Signed-off-by: Joel Becker <email@example.com>