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Allocating a NetDMA Channel

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Note  The NetDMA interface is not supported in Windows 8 and later.

Before using a dynamic memory access (DMA) channel, the NetDMA interface calls the ProviderAllocateDmaChannel function of the NetDMA provider driver to allocate and initialize the DMA channel.

The NetDMA interface supplies aNET_DMA_CHANNEL_PARAMETERS structure in the ChannelParameters parameter of ProviderAllocateDmaChannel. This parameters structure contains:

  • Information about the structure, including the revision number and size.

  • The virtual and physical address of the memory location that the NetDMA provider must use to write the completion status of a DMA operation on the DMA channel. These addresses are used if the NET_DMA_STATUS_UPDATE_ON_COMPLETION flag in the NET_DMA_DESCRIPTOR structure is set.

  • A bitmap that specifies the desired CPU affinities for the interrupt deferred procedure calls (DPCs) that are associated with DMA operations on the DMA channel.

  • The priority of the DMA channel.

If the NetDMA provider supports MSI-X and the CPU affinities of the interrupts that are associated with the DMA channels are set, the NetDMA provider driver attempts to allocate a DMA channel with an interrupt CPU affinity that matches a bit that is specified in the ProcessorAffinityMask member of the NET_DMA_CHANNEL_PARAMETERS structure. If MSI-X is not supported or MSI-X is supported but a DMA channel with a matching interrupt CPU affinity is not available, the NetDMA provider driver allocates any available DMA channel and calls the KeSetTargetProcessorDpc routine to set the target CPU of the interrupt DPC of the DMA channel to match one of the specified affinity mask bits.

In any situation, the NetDMA provider driver returns the CPU number that it associated with the interrupt DPC for the DMA channel to the NetDMA interface in the CpuNumber member of the NET_DMA_CHANNEL_PARAMETERS structure.

The NetDMA provider driver provides a pointer to a block of driver-allocated context information at the pProviderChannelContext parameter of ProviderAllocateDmaChannel. This context area stores information about the DMA channel. The NetDMA interface passes the context information in subsequent calls to ProviderXxx functions that require a DMA channel context.

When the NetDMA interface calls ProviderAllocateDmaChannel, the NetDMA interface provides a handle at the NetDmaChannelHandle parameter. The NetDMA provider driver uses this handle in subsequent calls to NetDmaXxx functions that are associated with the DMA channel.

If the NetDMA provider driver successfully allocates the DMA channel, the driver returns STATUS_SUCCESS from ProviderAllocateDmaChannel. After a DMA channel allocation succeeds, the driver must be ready for the NetDMA interface to use the channel in DMA transfers.

If the allocation fails for any reason, the driver should release any resources that it allocated in ProviderAllocateDmaChannel and return an appropriate return value from ProviderAllocateDmaChannel.

The NetDMA interface calls the ProviderFreeDmaChannel function to free a previously allocated DMA channel. For more information about freeing DMA channels, see Freeing a NetDMA Channel.