System for allocating buffer to transfer data when user buffer is mapped to physical region that does not conform to physical addressing limitations of controller

摘要

The present invention is a method and apparatus for efficiently transferring data between an input/output device and a main memory area of a computer system. More specifically, the invention transfers a requested amount of data using direct memory access and either a single transfer buffer or a dynamically allocated transfer buffer. The invention receives input/output requests that specify an amount of data to be transferred between the input/output device and a logical user buffer contained within the main memory area. By evaluating physical memory locations that correspond to the logical user buffer, the invention determines whether the physical memory locations conform to addressing limitations of a direct memory access transfer buffer. When the physical memory locations conform to the addressing limitations of a direct memory transfer buffer, the invention transfers the requested data directly between the input/output device and the physical memory locations of the logical user buffer. On the other hand, when the evaluated physical memory locations do not conform to the physical requirements of a direct memory access transfer buffer, the invention dynamically allocates a conforming direct memory access transfer buffer. Subsequently, the invention transfers the requested data between the input/output device and the conforming buffer. After transferring the data between the conforming buffer and the input/output device, the invention releases the allocated buffer to reduce the amount of memory overhead in the computer system.