FltIsOperationSynchronous function (fltkernel.h)

Article
11/30/2021

The FltIsOperationSynchronous routine determines whether a given callback data structure (FLT_CALLBACK_DATA) represents a synchronous or asynchronous I/O operation.

Syntax

BOOLEAN FLTAPI FltIsOperationSynchronous(
  [in] PFLT_CALLBACK_DATA CallbackData
);

Parameters

[in] CallbackData

Pointer to the callback data structure for the operation (FLT_CALLBACK_DATA).

Return value

FltIsOperationSynchronous returns TRUE if the operation is synchronous, and FALSE if the operation is asynchronous.

Remarks

FltIsOperationSynchronous determines whether a given callback data structure (FLT_CALLBACK_DATA) represents a synchronous or asynchronous I/O operation, according to the following conditions:

If the operation is not an IRP-based I/O operation, the operation is synchronous. To determine whether an operation is IRP-based, use the FLT_IS_IRP_OPERATION macro.
If the operation is an asynchronous paging I/O operation, the operation is asynchronous, even if one of the other conditions in this list is true.
If the operation is a synchronous paging I/O operation, the operation is synchronous.
If the file object for the operation was opened for synchronous I/O, the operation is synchronous.
If the IRP_SYNCHRONOUS_API flag is set in the IRP for the operation, the operation is synchronous. This flag is set for operations, such as IRP_MJ_QUERY_INFORMATION and IRP_MJ_SET_INFORMATION, that are always synchronous, even when performed on a file object that was opened for asynchronous I/O.
If none of the above conditions is true, the operation is asynchronous.

Note

FltIsOperationSynchronous also returns TRUE if the callback data structure represents an IRP_MJ_DEVICE_CONTROL, IRP_MJ_INTERNAL_DEVICE_CONTROL, or IRP_MJ_FILE_SYSTEM_CONTROL operation with an I/O control code (IOCTL) or file system control code (FSCTL) that was defined with METHOD_BUFFERED, even if the file object was opened for asynchronous I/O. Such a request is likely to be made synchronous by the file system, but this is not necessarily true in all cases.

When FltIsOperationSynchronous returns TRUE, this does not indicate that the I/O operation is synchronized. That is, the TRUE value does not indicate that a minifilter driver returned FLT_PREOP_SYNCHRONIZE in the preoperation callback (PFLT_POST_OPERATION_CALLBACK) routine for this operation. Instead, FltIsOperationSynchronous returns TRUE to indicate that the I/O operation is synchronous from the I/O manager's perspective.

FltIsOperationSynchronous can be called for all classes of operations: fast I/O, file system filter (FSFilter) callbacks, and IRP-based operations.

Requirements

Requirement	Value
Target Platform	Universal
Header	fltkernel.h (include Fltkernel.h)
Library	FltMgr.lib
DLL	Fltmgr.sys
IRQL	Any level