ADDRESS_AND_SIZE_TO_SPAN_PAGES

ULONG
ADDRESS_AND_SIZE_TO_SPAN_PAGES(
IN PVOID Va,
IN ULONG Size
);

ADDRESS_AND_SIZE_TO_SPAN_PAGES takes a virtual address and size in bytes of a transfer request and returns the number of pages spanned by the virtual range.

Parameters

Va

Points to the virtual address that is the base of the range.

Size

Specifies the size in bytes of the transfer request.

Return Value

ADDRESS_AND_SIZE_TO_SPAN_PAGES returns the number of pages for the virtual range starting at Va.

Comments

ADDRESS_AND_SIZE_TO_SPAN_PAGES is called by drivers that make DMA transfers to determine whether a given transfer request must be split up into a sequence of device DMA operations.

The system-defined constant PAGE_SIZE can be used to determine whether a given length in bytes for a transfer is less than the page size of the current platform.

Callers of ADDRESS_AND_SIZE_TO_SPAN_PAGES can be running at any IRQL, and usually run at IRQL DISPATCH_LEVEL.

See Also

IoMapTransfer