WdfDmaTransactionGetTransferInfo - NtDoc
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// wdfdmatransaction.h
VOID WdfDmaTransactionGetTransferInfo(
[in] WDFDMATRANSACTION DmaTransaction,
[out, optional] ULONG *MapRegisterCount,
[out, optional] ULONG *ScatterGatherElementCount
);
View the official Windows Driver Kit DDI referenceNo description available.
[Applies to KMDF only]
The WdfDmaTransactionGetTransferInfo method returns the number of map registers and scatter/gather list entries required for an initialized DMA transaction.
DmaTransaction [in]A handle to an initialized DMA transaction object.
MapRegisterCount [out, optional]A caller-supplied location that, on return, contains the number of map registers required for the specified transaction. This parameter is optional and can be NULL.
ScatterGatherElementCount [out, optional]A caller-supplied location that, on return, contains the number of scatter/gather elements required for the specified transaction. This parameter is optional and can be NULL.
The driver might call WdfDmaTransactionGetTransferInfo before calling WdfDmaTransactionAllocateResources or WdfDmaTransactionExecute.
When using DMA version 3, this method returns an accurate count of the number of map registers needed. When using earlier DMA versions, this method assumes that each page requires a map register.
WdfDmaTransactionAllocateResources