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Windows Driver Kit DDI reference (nc-vmbuskernelmodeclientlibapi-fn_vmb_channel_create_gpadl_from_mdl)

FN_VMB_CHANNEL_CREATE_GPADL_FROM_MDL callback function

Description

[Some information relates to pre-released product which may be substantially modified before it's commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here.]

The VmbChannelCreateGpadlFromMdl function creates a Guest Physical Address Descriptor List (GPADL) that describes a client-side buffer. The GPADL can be used in the server to access the buffer.

Parameters

`Channel`

A handle for a channel.

`Flags`

Flags. The possible values are the following:

Value	Meaning
VMBUS_CHANNEL_GPADL_READ_ONLY	If you specify this value, the buffer is read-only. Otherwise, the server can write to the buffer. This is not a security measure, but can improve snapshot and live migration performance.

`Mdl`

A pointer to a Memory Descriptor List (MDL) chain that describes the buffer. The buffer may have multiple pieces, which are chained by using the MDL next pointer.

`StartOffsetWithinMdl`

An offset, in bytes, in the MDL at which to start the mapping.

`DataLengthWithinMdl`

The length, in bytes, of the buffer chain. If this value is zero (0), use until the end of the MDL.

`GpadlHandle`

The GPADL handle of the created MDL. Send this to the server to use with the VmbChannelMapGpadl function.

Return value

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

Prototype

//Declaration

FN_VMB_CHANNEL_CREATE_GPADL_FROM_MDL FnVmbChannelCreateGpadlFromMdl;

// Definition

NTSTATUS FnVmbChannelCreateGpadlFromMdl
(
    VMBCHANNEL Channel
    UINT32 Flags
    PMDL Mdl
    UINT32 StartOffsetWithinMdl
    UINT32 DataLengthWithinMdl
    PUINT32 GpadlHandle
)
{...}

Remarks

When this function returns, the server endpoint can call VmbChannelMapGpadl, because VMBus will already have send the GPADL description to the opposite endpoint and received confirmation.

The GPADL must be deleted by using the VmbChannelDeleteGpadl function.

[!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.

FN_VMB_CHANNEL_CREATE_GPADL_FROM_MDL - NtDoc