FltCreateSectionForDataScan function (fltkernel.h)

Article
12/07/2021

The FltCreateSectionForDataScan routine creates a section object for a file. The filter manager can optionally synchronize I/O with the section created.

Syntax

NTSTATUS FLTAPI FltCreateSectionForDataScan(
  [in]            PFLT_INSTANCE      Instance,
  [in]            PFILE_OBJECT       FileObject,
  [in]            PFLT_CONTEXT       SectionContext,
  [in]            ACCESS_MASK        DesiredAccess,
  [in, optional]  POBJECT_ATTRIBUTES ObjectAttributes,
  [in, optional]  PLARGE_INTEGER     MaximumSize,
  [in]            ULONG              SectionPageProtection,
  [in]            ULONG              AllocationAttributes,
  [in]            ULONG              Flags,
  [out]           PHANDLE            SectionHandle,
  [out]           PVOID              *SectionObject,
  [out, optional] PLARGE_INTEGER     SectionFileSize
);

Parameters

[in] Instance

The opaque instance pointer for the minifilter driver instance whose context is to be retrieved.

[in] FileObject

The file object for an open file. The section object will be backed by the specified file. This parameter is required and cannot be NULL.

[in] SectionContext

A pointer to a previously allocated section context.

[in] DesiredAccess

The type of access for the section object as one or more of the following ACCESS_MASK flags.

Flag	Allows caller to
SECTION_MAP_READ	Read views of the section.
SECTION_MAP_WRITE	Write views of the section.
SECTION_QUERY	Query the section object for information about the section. Drivers should set this flag.
SECTION_ALL_ACCESS	All actions defined by the previous flags as well as that defined by STANDARD_RIGHTS_REQUIRED. For more information about STANDARD_RIGHTS_REQUIRED, see ACCESS_MASK.

[in, optional] ObjectAttributes

A pointer to an optional OBJECT_ATTRIBUTES structure that specifies the object name and other attributes. Use the InitializeObjectAttributes macro to initialize this structure.

[in, optional] MaximumSize

This parameter is reserved for future use.

[in] SectionPageProtection

The protection to place on each page in the section. Specify one of the following values. This parameter is required and cannot be zero.

Flag	Meaning
PAGE_READONLY	Enables read-only access to the committed region of pages. An attempt to write to the committed region results in an access violation. If the system differentiates between read-only access and execute access, an attempt to execute code in the committed region results in an access violation.
PAGE_READWRITE	Enables both read and write access to the committed region of pages.

[in] AllocationAttributes

Bitmasks of the SEC_XXX flags determine the allocation attributes of the section. Specify one or more of the following values. This parameter is required and cannot be zero.

Flag	Meaning
SEC_COMMIT	Allocates physical storage in memory or in the paging file on disk for all pages of a section. This is the default setting. Note that this flag is required and cannot be omitted.
SEC_FILE	The file specified by the FileObject parameter is a mapped file.

[in] Flags

This parameter is reserved for future use.

[out] SectionHandle

A pointer to a caller-allocated variable that receives an opaque handle to the section. By default, the section handle is a user handle. If the caller needs a kernel handle, they must pass in a pointer to an initialized OBJECT_ATTRIBUTES structure in the ObjectAttributes parameter with the OBJ_KERNEL_HANDLE flag set.

[out] SectionObject

A pointer to a caller-allocated variable that receives an opaque pointer to the section object.

[out, optional] SectionFileSize

A pointer to a caller-allocated variable that receives the size, in bytes, of the file at the time the section object was created. This parameter is optional and can be NULL.

Return value

FltCreateSectionForDataScan returns STATUS_SUCCESS or an appropriate NTSTATUS value, such as one of the following.

Return code	Description
STATUS_END_OF_FILE	The size of the file specified by the FileObject parameter is zero.
STATUS_FILE_LOCK_CONFLICT	The file specified by the FileObject parameter is locked.
STATUS_INSUFFICIENT_RESOURCES	FltCreateSectionForDataScan encountered a pool allocation failure.
STATUS_INVALID_FILE_FOR_SECTION	The file specified by the FileObject parameter does not support sections.
STATUS_INVALID_PARAMETER	The minifilter is not registered.
STATUS_INVALID_PARAMETER_8	The value specified for the SectionPageProtection parameter is invalid.
STATUS_INVALID_PARAMETER_9	The caller specified an invalid value for the AllocationAttributes parameter.
STATUS_NOT_SUPPORTED	The volume attached to this instance does not support section contexts.
STATUS_PRIVILEGE_NOT_HELD	The caller did not have the required privileges to create a section object with the access specified in the DesiredAccess parameter.
STATUS_FILE_IS_A_DIRECTORY	The file specified by the FileObject parameter is a directory.
STATUS_FLT_CONTEXT_ALREADY_DEFINED	The filter instance specified by Instance already has an open section for the stream. Only one section per stream, and therefore, per instance is supported.

Remarks

Prior to calling FltCreateSectionForDataScan, a minifilter must first register its volume for data scanning by calling FltRegisterForDataScan. As with other filter context elements, SectionContext is first allocated with FltAllocateContext.

FltCreateSectionForDataScan inserts the handle to the object (SectionHandle) into the process handle table for the thread that FltCreateSectionForDataScan is called on.

Handles can be either user handles or kernel handles. A handle created with OBJ_KERNEL_HANDLE set in the OBJECT_ATTRIBUTES structure that ObjectAttributes points to is a kernel handle, and can only be accessed from kernel mode. A handle created without the OBJ_KERNEL_HANDLE flag is a user handle, which can be accessed from user or kernel mode. A filter can create a user handle and then pass it to a user-mode application for processing. For example, a virus scanning engine can live in a user-mode application and be fed user handles from a file system filter.

Certain situations can occur where holding a section open is incompatible with current file I/O. In particular, file I/O that triggers a cache purge can cause cache incoherency if the cache purge is prevented because of an open section. A minifilter can provide an optional callback routine for notifications of these events. The minifilter driver implements a PFLT_SECTION_CONFLICT_NOTIFICATION_CALLBACK to receive these notifications. Conflict notifications are enabled if the SectionNotificationCallback member of FLT_REGISTRATION is set to this callback routine when the minifilter is registered. When a notification is received, the section can be closed to allow the conflicting I/O operation to continue.

Note

A section notification callback might occur before FltCreateSectionForDataScan returns. A minifilter must be able to receive the callback and handle the case where SectionHandle and SectionObject are not yet valid.

When the section object created by this routine is no longer necessary, be sure to close the section object's handle (SectionHandle) by calling the ZwClose routine and dereference the section object itself (SectionObject) by calling the ObDereferenceObject routine.

For overview information on creating mapped sections and views of memory, see Section Objects and Views. Also, see the documentation for the CreateFileMapping routine in the Microsoft Windows SDK.

Important

Minifilters must not explicitly delete a section context passed to FltCreateSectionForDataScan. Do not call FltDeleteContext after a section context is passed to FltCreateSectionForDataScan. A section context is deallocated and removed from a stream by calling FltCloseSectionForDataScan in this case.

In general, sections should be created as read-only. In particular, if a read-only file is in a transaction and a minifilter does not create a read-only section, a write to the section is discarded and is not included as part of the transaction.

Requirements

Requirement	Value
Minimum supported client	Windows 8
Target Platform	Universal
Header	fltkernel.h (include Fltkernel.h)
Library	FltMgr.lib
IRQL	<= APC_LEVEL