Implementing extent granularity authorization processing in CAPI adapters

A method, system and computer program product are provided for implementing block extent granularity authorization processing for a Coherent Accelerator Processor Interface (CAPI) adapter. An Application Client requests authorization to a File from a system processor file system. The file system validates the request, determines the location of each Extent that comprises the File, and requests authorization to each Extent from a System CAPI Authorization manager. The System CAPI Authorization manager requests the CAPI Client manager to assign a Child Client ID and CAPI Server Register range to the requesting Application Client and requests a previously authorized CAPI Parent Client to authorize the Child ID to the list of Extents. The CAPI Parent Client sends a Create Authorizations command to the CAPI Adapter via the Parent's CAPI Server Registers. The CAPI Adapter validates the Parent Authorization Handle and CPI Server Register range for the specific Extent/Command/Resource, and creates an Authorization List by assigning a new Child Authorization Handle for each requested, validated Extent/Command/Resource. The Authorization List and the Child Client ID are returned to the File System.