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

In a computer system having a memory area, a secondary storage area, and a direct memory access controller for transferring data between the secondary storage area and a transfer buffer contained in the memory area, an apparatus for processing a memory transfer request from an application program that specifies an amount of data and a user buffer, the user buffer being mapped to a physical memory region of the memory area and being used to hold transferred data for the application program, the apparatus comprising:

• an evaluator to determine whether the user buffer is mapped to a physical memory region of said memory area which conforms to the physical addressing limitations of the direct memory access controller;
• a single buffer programming device for programming the direct memory access controller to transfer the specified amount of data using the physical memory region as the transfer buffer when the physical memory region conforms to the physical addressing limitations of the direct memory access controller;
• and
• an allocator for allocating a conforming buffer in the memory area to be used as the transfer buffer when the physical memory region does not conform to the physical addressing limitations of the direct memory access controller, the conforming buffer being a buffer which conforms to the physical addressing limitations of the direct memory access controller.

In a computer system having a memory area, a secondary storage, a direct memory access (DMA) controller for controlling DMA transfers between the secondary storage and the memory area, a method comprising the computer-implemented steps of:

• providing an application buffer in the memory area for storing data for an application program;
• determining whether the DMA controller can correctly access the application buffer to buffer data on behalf of the DMA controller;
• where the DMA controller cannot correctly access the application buffer, dynamically allocating a DMA transfer buffer that the DMA controller can correctly access;
• performing a DMA data transfer on behalf of the application program such that the DMA transfer buffer is used to buffer data;
• and
• deallocating the DMA transfer buffer after the DMA data transfer is complete.

A computer readable storage medium holding a computer code for use in a computer system that includes a memory area, a secondary storage area, and a direct memory access controller for transferring data between the secondary storage area and the memory area, said computer code, when executed, performing the steps of:

• determining physical addressing limitations of the direct memory access controller;
• determining when a user buffer is mapped to a physical memory region that conforms to the physical addressing limitations of the direct memory access controller;
• when the user buffer is mapped to a physical memory region that conforms to the physical addressing limitations of the direct memory access controller, transferring the specified amount of data between the physical memory region and the secondary storage area via the direct memory access controller;
• and
• when the user buffer is mapped to a physical memory region of said memory area that does not conform to the physical addressing limitations of the direct memory access controller, dynamically allocating a conforming buffer in the memory area for use in transferring the specified amount of data, the conforming buffer being a buffer which conforms to the physical addressing limitations of the direct memory access controller.

A computer readable storage medium holding computer code for use in a computer system having a memory, a secondary storage, a direct memory access (DMA) controller for controlling DMA transfers between the secondary storage and the memory area, the computer code, when executed, performing the steps of:

• providing an application buffer in the memory area for storing data for an application program;
• determining whether the DMA controller can correctly access the application buffer to buffer data on behalf of the DMA controller;
• where the DMA controller cannot correctly access the application buffer, dynamically allocating a DMA transfer buffer that the DMA controller can correctly access;
• performing a DMA data transfer on behalf of the application program such that the DMA transfer buffer is used to buffer data;
• and
• deallocating the DMA transfer buffer after the DMA data transfer is complete.