FLT_IO_PARAMETER_BLOCK structure (fltkernel.h)

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05/31/2024

The FLT_IO_PARAMETER_BLOCK structure contains the parameters for the I/O operation represented by a FLT_CALLBACK_DATA callback data structure.

Syntax

typedef struct _FLT_IO_PARAMETER_BLOCK {
  ULONG          IrpFlags;
  UCHAR          MajorFunction;
  UCHAR          MinorFunction;
  UCHAR          OperationFlags;
  UCHAR          Reserved;
  PFILE_OBJECT   TargetFileObject;
  PFLT_INSTANCE  TargetInstance;
  FLT_PARAMETERS Parameters;
} FLT_IO_PARAMETER_BLOCK, *PFLT_IO_PARAMETER_BLOCK;

Members

IrpFlags

A bitmask of flags that specify various aspects of the I/O operation. These flags are used only for IRP-based operations. The following table shows flag values.

Value	Meaning
IRP_BUFFERED_IO	The operation is a buffered I/O operation.
IRP_CLOSE_OPERATION	The operation is a cleanup or close operation.
IRP_DEALLOCATE_BUFFER	The I/O Manager will free the buffer during the completion phase for the IRP.
IRP_INPUT_OPERATION	The operation is an input operation.
IRP_NOCACHE	The operation is a noncached I/O operation.
IRP_PAGING_IO	The operation is a paging I/O operation.
IRP_SYNCHRONOUS_API	The I/O operation is synchronous.
IRP_SYNCHRONOUS_PAGING_IO	The operation is a synchronous paging I/O operation.
IRP_MOUNT_COMPLETION	A volume mount is completed for the operation.
IRP_CREATE_OPERATION	The operation is a create or open operation.
IRP_READ_OPERATION	The I/O operation is for reading.
IRP_WRITE_OPERATION	The I/O operation is for writing.
IRP_DEFER_IO_COMPLETION	I/O completion of the operation is deferred.
IRP_ASSOCIATED_IRP	The operation is associated with a master IRP.
IRP_OB_QUERY_NAME	The operation is an asynchronous name query.
IRP_HOLD_DEVICE_QUEUE	Reserved.
IRP_UM_DRIVER_INITIATED_IO	The operation originated from a user-mode driver.

MajorFunction

The major function code for the I/O operation. Major function codes are used for IRP-based operations, fast I/O operations, and file system (FSFilter) callback operations. For more information about additional operations, see FLT_PARAMETERS.

MinorFunction

The minor function code for the I/O operation. This member is optional and can be NULL. The value of the MajorFunction member determines the possible values. For more information about minor function codes, see FLT_PARAMETERS.

OperationFlags

A bitmask of flags that specify various aspects of the I/O operation. These flags are used only for IRP-based operations. The Filter Manager copies these flags from the Flags member of the IO_STACK_LOCATION structure that is associated with the IRP. The following table shows the most commonly used flag values.

Value	Meaning
SL_CASE_SENSITIVE	Used for IRP_MJ_CREATE. If this flag is set, file name comparisons should be case-sensitive.
SL_EXCLUSIVE_LOCK	Used for IRP_MJ_LOCK_CONTROL. If this flag is set, an exclusive byte-range lock is requested. Otherwise, a shared lock is requested.
SL_FAIL_IMMEDIATELY	Used for IRP_MJ_LOCK_CONTROL. If this flag is set, the lock request should fail if it cannot be granted immediately.
SL_FORCE_ACCESS_CHECK	Used for IRP_MJ_CREATE. If this flag is set, access checks must be performed even if the value of the IRP's RequestorMode member is KernelMode.
SL_FORCE_DIRECT_WRITE	Used for IRP_MJ_WRITE and IOCTL_DISK_COPY_DATA. If this flag is set, kernel-mode drivers can write to volume areas that they are normally blocked from writing to due to security reasons. This flag is checked both at the file system layer and storage stack layer. The SL_FORCE_DIRECT_WRITE flag is available in Windows Vista and later versions of Windows.
SL_INDEX_SPECIFIED	Used for IRP_MJ_DIRECTORY_CONTROL, IRP_MJ_QUERY_EA, and IRP_MJ_SET_QUOTA. If this flag is set, the scan for directory, quota, or extended-attribute information should begin at the entry in the list whose index is specified.
SL_OPEN_PAGING_FILE	Used for IRP_MJ_CREATE. If this flag is set, the file is a paging file.
SL_OPEN_TARGET_DIRECTORY	Used for IRP_MJ_CREATE. If this flag is set, the file's parent directory should be opened.
SL_OVERRIDE_VERIFY_VOLUME	Used for IRP_MJ_DIRECTORY_CONTROL, IRP_MJ_READ, and IRP_MJ_WRITE. If this flag is set, the I/O operation should be performed even if the DO_VERIFY_VOLUME flag is set on the volume's device object.
SL_RESTART_SCAN	Used for IRP_MJ_DIRECTORY_CONTROL, IRP_MJ_QUERY_EA, and IRP_MJ_SET_QUOTA. If this flag is set, the scan for directory, quota, or extended-attribute information should begin at the first entry in the directory or list. Otherwise, the scan should be resumed from the previous scan.
SL_RETURN_SINGLE_ENTRY	Used for IRP_MJ_DIRECTORY_CONTROL, IRP_MJ_QUERY_EA, and IRP_MJ_SET_QUOTA. If this flag is set, the scan for directory, quota, or extended-attribute information should return only the first entry that is found.
SL_WATCH_TREE	Used for IRP_MJ_DIRECTORY_CONTROL. If this flag is set, all subdirectories of this directory should also be watched. Otherwise, only the directory itself is to be watched.
SL_WRITE_THROUGH	Used for IRP_MJ_WRITE. If this flag is set, the file data must be written through to persistent storage, not just written to the cache.

Reserved

Reserved for system use. Do not use.

TargetFileObject

A file object pointer for the file or directory that is the target for this I/O operation.

TargetInstance

An opaque instance pointer for the minifilter that is the target for this I/O operation.

Parameters

An FLT_PARAMETERS structure that contains the parameters for the I/O operation that are specified by the MajorFunction and MinorFunction members.

Remarks

The FLT_IO_PARAMETER_BLOCK structure contains the parameters for the I/O operation that is represented by a callback data (FLT_CALLBACK_DATA) structure. The callback data structure contains a pointer to the FLT_IO_PARAMETER_BLOCK structure in its Iopb member.

A minifilter receives a pointer to the callback data structure as the Data or CallbackData input parameter to the following callback routine types:

A minifilter's preoperation and postoperation callback routines can modify the contents of the FLT_IO_PARAMETER_BLOCK structure for the I/O operation, except for the MajorFunction and Reserved members. If it does, it must call FltSetCallbackDataDirty, unless it has also modified the IoStatus member of the callback data structure for the operation. Otherwise, the modified values are ignored.

When Filter Manager issues a preoperation or postoperation callback to a minifilter, FltObjects->FileObject and TargetFileObject (CallbackData->Iopb->TargetFileObject) are initially the same. If a minifilter modifies TargetFileObject or TargetInstance, its subsequent call to FltSetCallbackDataDirty from a preoperation callback will cause Filter Manager to replace FltObjects->FileObject and FltObjects->Instance before sending the operation to lower filters.

If a minifilter's preoperation callback routine modifies the parameters for an I/O operation, all minifilters below it in the minifilter instance stack will receive the modified parameters in their preoperation and postoperation callback routines.

The modified parameters are not received by the minifilter's own postoperation callback routine, or by any minifilters above that minifilter in the minifilter instance stack. In all cases, a minifilter's preoperation and postoperation callback routines receive the same input parameter values.

If a minifilter changes the value of the TargetInstance member, the new value must be a pointer to an instance of the same minifilter at the same altitude on a different volume. In addition, the new volume's device object must have a stack size that is greater than or equal to that of the original volume's device object.

To get the stack size for a volume device object, given an opaque instance pointer for an instance that is attached to the volume, do the following:

Call FltGetVolumeFromInstance to get the volume pointer.
Call FltGetDeviceObject to get a pointer to the volume device object. This pointer is returned in the DeviceObject parameter. The device object's stack size can be found in DeviceObject->StackSize.
When the volume pointer is no longer needed, call FltObjectDereference to decrement its reference count.
When the volume device object pointer is no longer needed, call ObDereferenceObject to decrement its reference count.

A minifilter can change the value of the TargetFileObject member. However, the new value must be a pointer to a file object for a file that resides on the same volume as the instance specified by the TargetInstance member.

A minifilter cannot safely change the value of the MajorFunction member. Instead, it must initiate a new I/O operation.

A minifilter can initiate an I/O operation by calling a support routine such as FltReadFile or by calling FltAllocateCallbackData to allocate a callback data structure; initializing the I/O parameters in the FLT_IO_PARAMETER_BLOCK structure, and passing the callback data structure to FltPerformSynchronousIo or FltPerformAsynchronousIo.

Note

Use support routines wherever possible when initiating I/O operations. A minifilter should allocate its own callback data only if there is no support function for a particular I/O operation.

Requirements

Requirement	Value
Header	fltkernel.h (include Fltkernel.h)

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FLT_IO_PARAMETER_BLOCK structure (fltkernel.h)

Syntax

Members

Remarks

Requirements

See also

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