IoCreateStreamFileObject routine

The IoCreateStreamFileObject routine creates a new stream file object.

Syntax


PFILE_OBJECT IoCreateStreamFileObject(
  _In_opt_ PFILE_OBJECT   FileObject,
  _In_opt_ PDEVICE_OBJECT DeviceObject
);

Parameters

FileObject [in, optional]

Pointer to the file object to which the new stream file is related. This parameter is optional and can be NULL.

DeviceObject [in, optional]

Pointer to a device object for the device on which the stream file is to be opened. If the caller specifies a non-NULL value for FileObject, the value of DeviceObject is ignored. Otherwise, the caller must specify a non-NULL value for DeviceObject.

Return value

IoCreateStreamFileObject returns a pointer to the newly created stream file object.

Remarks

File systems call IoCreateStreamFileObject to create a new stream file object. A stream file object is identical to an ordinary file object, except that the FO_STREAM_FILE file object flag is set.

A stream file object is commonly used to represent an internal stream for a volume mounted by the file system. This virtual volume file permits the file system to view, change, and cache the volume's on-disk structure as if it were an ordinary file. In this case, the DeviceObject parameter in the call to IoCreateStreamFileObject specifies the volume device object (VDO) for the volume.

A stream file object can also be used to represent an alternate data stream for accessing a file's metadata, such as extended attributes or security descriptors. In this case, the FileObject parameter in the call to IoCreateStreamFileObject specifies an existing file object for the file. The newly created stream file object permits the file system to view, change, and cache the file's metadata as if it were an ordinary file.

When the stream file object is no longer needed, the caller must decrement its reference count by calling ObDereferenceObject. When the stream file object's reference count reaches zero, an IRP_MJ_CLOSE request is sent to the file system driver stack for the volume.

File system filter driver writers should note that IoCreateStreamFileObject causes an IRP_MJ_CLEANUP request to be sent to the file system driver stack for the volume. Because file systems often create stream file objects as a side effect of operations other than IRP_MJ_CREATE, it is difficult for filter drivers to reliably detect stream file object creation. Thus a filter driver should expect to receive IRP_MJ_CLEANUP and IRP_MJ_CLOSE requests for previously unseen file objects.

If a pool allocation failure occurs, IoCreateStreamFileObject raises a STATUS_INSUFFICIENT_RESOURCES exception.

Requirements

Target platform

Universal

Header

Ntifs.h (include Ntifs.h)

Library

NtosKrnl.lib

DLL

NtosKrnl.exe

IRQL

<= DISPATCH_LEVEL

See also

IoCreateStreamFileObjectEx
IoCreateStreamFileObjectLite
IRP_MJ_CLEANUP
IRP_MJ_CLOSE
IRP_MJ_CREATE
ObDereferenceObject

 

 

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