FltAllocateCallbackDataEx routine

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 FltAllocateCallbackDataEx(
  _In_     PFLT_INSTANCE                    Instance,
  _In_opt_ PFILE_OBJECT                     FileObject,
  _Out_    PFLT_CALLBACK_DATA               *RetNewCallbackData


Instance [in]

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

FileObject [in, optional]

A pointer to a file object to be used in the I/O operation. This parameter is optional and can be NULL.

Flags [in]

A value of zero or the following flag:


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.

RetNewCallbackData [out]

A 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.

Note   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.

Set FileObject to NULL if this is a CREATE operation.

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


Target platform



Available in Windows 7 and later versions of the Windows operating system.


Fltkernel.h (include FltKernel.h)





See also




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