FltAllocateCallbackDataEx function (fltkernel.h)

The FltAllocateCallbackDataEx routine allocates a callback data structure and can preallocate memory for additional structures that a minifilter driver can use to initiate an I/O request.


NTSTATUS FLTAPI FltAllocateCallbackDataEx(
  [in]          PFLT_INSTANCE                    Instance,
  [in/optional] PFILE_OBJECT                     FileObject,
  [out]         PFLT_CALLBACK_DATA               *RetNewCallbackData


[in] Instance

Opaque instance pointer to the minifilter driver instance that is initiating the I/O operation. This parameter is required and cannot be NULL.

[in/optional] FileObject

Pointer to a file object to be used in the I/O operation. This parameter is optional and can be NULL. Set FileObject to NULL if this is a CREATE operation.

[in] Flags

A value of zero or the following flag: FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY

If this flag is set, the routine preallocates all the memory needed by the filter manager for additional structures to be used in an I/O request.

[out] RetNewCallbackData

Pointer to a caller-allocated variable that receives the address of the newly allocated callback data FLT_CALLBACK_DATA structure.

Return value

The FltAllocateCallbackDataEx routine returns STATUS_SUCCESS on success or STATUS_INSUFFICIENT_RESOURCES if the routine encountered a pool allocation failure when attempting to allocate the callback data structure or if the FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY flag is set and additional memory could not be allocated.


If the FLT_ALLOCATE_CALLBACK_DATA_PREALLOCATE_ALL_MEMORY flag is set, the routine allocates all the memory needed for additional filter manager structures to be used in a subsequent I/O request. Using this flag enables a minifilter to preallocate one or more callback data structures to be used for issuing I/O requests under low memory conditions or in situations where recovering from a memory allocation failure might be complicated.


The additional allocated memory is for use by the filter manager. The file system or other filters can still fail the I/O request due to an out-of-memory condition.


The comments for FltAllocateCallbackData apply to FltAllocateCallbackDataEx as well. Review that information in order to select the correct routine for your design.


Minimum supported client Available in Windows 7 and later versions of the Windows operating system.
Target Platform Universal
Header fltkernel.h (include FltKernel.h)
Library FltMgr.lib

See also