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.
Syntax
NTSTATUS FLTAPI FltAllocateCallbackDataEx(
[in] PFLT_INSTANCE Instance,
[in/optional] PFILE_OBJECT FileObject,
[in] FLT_ALLOCATE_CALLBACK_DATA_FLAGS Flags,
[out] PFLT_CALLBACK_DATA *RetNewCallbackData
);
Parameters
[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.
Remarks
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.
Important
The comments for FltAllocateCallbackData apply to FltAllocateCallbackDataEx as well. Review that information in order to select the correct routine for your design.
Requirements
| Requirement | Value |
|---|---|
| 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 |
| IRQL | <= APC_LEVEL |