1. A dynamic cache system for use with a data storage system having a data access interface and a storage device with a data path therebetween, the dynamic cache system comprising: a cache controller coupled to the data path between the storage device and the data access interface, the cache controller registering to be called by a filter framework in response to an I/O operation on the data path between the data access interface and the data storage device to control caching of data accessed through the I/O operation; a storage memory accessible by the cache controller and configurable by the cache controller to be an intermediate storage for the data accessed through the I/O operation on the data path under control of the cache controller; and a caching definition accessible by the cache controller having a predetermined criteria for prompting caching activity by the cache controller, the cache controller being responsive to the predetermined criteria to provide selective caching of the data in the storage memory such that the data associated with the I/O operation is cached or prevented from being cached based on the predetermined criteria.