FN_VMB_PACKET_SEND_WITH_EXTERNAL_MDL callback function (vmbuskernelmodeclientlibapi.h)

Article
04/01/2021

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The VmbPacketSendWithExternalMdl function sends the data in a packet buffer or external data Memory Descriptor List (MDL). The function associates that data with the VMBus packet object, which represents the packet throughout the lifetime of the transaction.

Syntax

FN_VMB_PACKET_SEND_WITH_EXTERNAL_MDL FnVmbPacketSendWithExternalMdl;

NTSTATUS FnVmbPacketSendWithExternalMdl(
  __drv_aliasesMem VMBPACKET PacketObject,
  PVOID Buffer,
  UINT32 BufferLength,
  PMDL ExternalDataMdl,
  UINT32 MdlOffset,
  UINT32 MdlLength,
  UINT32 Flags
)
{...}

Parameters

PacketObject

A handle to the VMBus packet object.

Buffer

A buffer that contains the command packet that is sent through the VMBus ring buffer.

BufferLength

The length, in bytes, of the buffer in the Buffer parameter.

ExternalDataMdl

An MDL that describes a data buffer associated with the packet.

MdlOffset

The offset from the buffer described by the MDL where the data starts.

MdlLength

The length of the sub-buffer to send. Use 0 for the entire MDL.

Flags

Flags. The following are pertinent flags:

Value	Meaning
VMBUS_CHANNEL_FORMAT_FLAG_WAIT_FOR_COMPLETION	This packet cannot be considered complete and its resources cannot be released until a completion packet comes back from the opposite endpoint. This flag must be set.
VMBUS_CHANNEL_FORMAT_FLAG_FORCE_MDL_LENGTH	Always use MdlLength for the length of the external data MDL, even if this length is longer than the ByteCount field of the MDL. This only allows exceeding the length of the MDL by rounding up to a page boundary. If this flag is set, only the first MDL in the MDL chain is used.
VMBUS_CHANNEL_FORMAT_FLAG_PAGED_BUFFER	The inline buffer is paged and must be treated accordingly, which means it must be copied before entering DPC level. Probing user-mode buffers or handling access violations is the responsibility of the caller.

Return value

Returns STATUS_SUCCESS if the operation succeeds, or an appropriate NTSTATUS error code otherwise.

Remarks

This function differs from the VmbPacketSend function in that it allows passing an MDL offset and MDL length.

Important

This function is called through the VMBus Kernel Mode Client Library (KMCL) interface, provided by the Vmbkmcl.sys bus driver. This is a client function accessed from the KMCL_CLIENT_INTERFACE_V1 structure.

For more information, see the Remarks section of the KMCL_CLIENT_INTERFACE_V1.

Requirements

Requirement	Value
Minimum supported client	Windows 10, version 1803
Header	vmbuskernelmodeclientlibapi.h