SYSTEM AND METHOD FOR EFFICIENTLY TRANSFERRING DATASTREAMS IN A MULTIMEDIA SYSTEM

摘要

A general purpose interface is provided to a file system of a multimedia ser ver for improving datastream throughput by avoiding data copying and context switchi ng. The file system includes an export registration service providing function pointers t o the file system's implementation of a predefined set of zero copy interfaces. These i nterfaces include an initialization service to set up necessary data structures and to place use counts on objects to prevent them from being removed while zero copy operations are in progress. A termination service in the zero copy interfaces cleans up data structures and removes use counts. Additional services validate that a specified file is suitable f or zero copy operations, find and record file attributes needed to later acquire buffers at interrupt level. A data structure is defined to hold these attributes for subsequent calls. A nother service locks a buffer at an interrupt level and returns the amount of data present, and provides addressability to the buffer in another address space context. A data struct ure holds these buffer attributes for subsequent calls. A service is additionally provided t o unlock the buffer at interrupt level. Finally, a service provides information on changes to th e access pattern of the file such as would be needed to support VCR functions. Ahash chain em ploying a singly linked list updated atomically allows for safe buffer lookups at inte rrupt level. Compare-and-swap locking facilitates this. A mailbox interface useful at int errupt level provides prefetch and release information to the daemon. In case of a lock c ollision or where the buffer is not available, the buffer is acquired in a process conte xt.