PFLT_CONTEXT_ALLOCATE_CALLBACK callback function (fltkernel.h)

A minifilter driver can register a routine of type PFLT_CONTEXT_ALLOCATE_CALLBACK as the minifilter driver's ContextAllocateCallback routine.

Syntax

PFLT_CONTEXT_ALLOCATE_CALLBACK PfltContextAllocateCallback;

PVOID PfltContextAllocateCallback(
  [in] POOL_TYPE PoolType,
  [in] SIZE_T Size,
  [in] FLT_CONTEXT_TYPE ContextType
)
{...}

Parameters

[in] PoolType

The type of pool to allocate. This parameter is required and must be one of the following:

NonPagedPool

PagedPool

Must be NonPagedPool if the ContextType parameter is FLT_VOLUME_CONTEXT.

[in] Size

The size, in bytes, of the entire context, including both the portion defined by the filter manager and the portion defined by the minifilter driver.

[in] ContextType

The type of context. This parameter is required and must be one of the following values:

FLT_FILE_CONTEXT (starting with Windows Vista)

FLT_INSTANCE_CONTEXT

FLT_STREAM_CONTEXT

FLT_STREAMHANDLE_CONTEXT

FLT_SECTION_CONTEXT (starting with Windows 8)

FLT_TRANSACTION_CONTEXT (starting with Windows Vista)

FLT_VOLUME_CONTEXT

Return value

If not enough free pool is available to satisfy the request, this routine returns a NULL pointer. Otherwise, it returns a pointer to the newly allocated context.

Remarks

For the rare cases that a minifilter driver must perform its own context allocation, it can specify a routine of type PFLT_CONTEXT_ALLOCATE_CALLBACK as the ContextAllocateCallback routine for each context type that it registers when it calls FltRegisterFilter from its DriverEntry routine. To specify this routine, the minifilter driver stores a pointer to the routine in the ContextAllocateCallback member of the FLT_CONTEXT_REGISTRATION structure for the context type.

For more information about context registration, see the reference entry for FLT_CONTEXT_REGISTRATION.

Requirements

See also

FLT_CONTEXT_REGISTRATION

FLT_REGISTRATION

FltRegisterFilter

PFLT_CONTEXT_CLEANUP_CALLBACK

PFLT_CONTEXT_FREE_CALLBACK