N-port virtualization driver-based application programming interface and split driver implementation

An API in an NPIV-compatible SAN is disclosed that includes functions for creating a vlink, replicating driver software for managing the vlink, monitoring resources in an HBA, or removing a target so that resources can be freed up for other vlinks. The API is part of a driver that communicates with a host OS and also communicates with an HBA to establish the vlinks between the host OS and FC devices. To create vlinks, an "add" function in the API is called by the OS. In addition, when a new vlink is created, a single version of an HBA interface function block is maintained in the driver, but a discovery function block, SCSI bus function block, and I/O function block are all duplicated, forming one logical vlink driver for each vlink. To obtain HBA resource information, a resource monitoring functions in the API may be called by the OS.