Creates a new file or directory, or opens an existing file, device, directory, or volume.

This function is equivalent to the ZwCreateFile function documented in the Microsoft Windows Driver Kit (WDK).

Syntax

NTSTATUS NtCreateFile(
  __out     PHANDLE FileHandle,
  __in      ACCESS_MASK DesiredAccess,
  __in      POBJECT_ATTRIBUTES ObjectAttributes,
  __out     PIO_STATUS_BLOCK IoStatusBlock,
  __in_opt  PLARGE_INTEGER AllocationSize,
  __in      ULONG FileAttributes,
  __in      ULONG ShareAccess,
  __in      ULONG CreateDisposition,
  __in      ULONG CreateOptions,
  __in      PVOID EaBuffer,
  __in      ULONG EaLength
);

Parameters

FileHandle [out]

A pointer to a variable that receives the file handle if the call is successful.

DesiredAccess [in]

The ACCESS_MASK value that expresses the type of access that the caller requires to the file or directory. The set of system-defined DesiredAccess flags determines the following specific access rights for file objects.

Value	Meaning
DELETE	The file can be deleted.
FILE_READ_DATA	Data can be read from the file.
FILE_READ_ATTRIBUTES	FileAttributes flags, described later, can be read.
FILE_READ_EA	Extended attributes associated with the file can be read. This flag is irrelevant to device and intermediate drivers.
READ_CONTROL	The access control list (ACL) and ownership information associated with the file can be read.
FILE_WRITE_DATA	Data can be written to the file.
FILE_WRITE_ATTRIBUTES	FileAttributes flags can be written.
FILE_WRITE_EA	Extended attributes (EAs) associated with the file can be written. This flag is irrelevant to device and intermediate drivers.
FILE_APPEND_DATA	Data can be appended to the file.
WRITE_DAC	The discretionary access control list (DACL) associated with the file can be written.
WRITE_OWNER	Ownership information associated with the file can be written.
SYNCHRONIZE	The returned FileHandle can be waited on to synchronize with the completion of an I/O operation.
FILE_EXECUTE	Data can be read into memory from the file using system paging I/O. This flag is irrelevant to device and intermediate drivers.

 

Callers of NtCreateFile can specify one or a combination of the following, possibly ORed with additional compatible flags from the preceding DesiredAccess flags list, for any file object that does not represent a directory file.

Value	Meaning
GENERIC_READ	STANDARD_RIGHTS_READ, FILE_READ_DATA, FILE_READ_ATTRIBUTES, and FILE_READ_EA
GENERIC_WRITE	STANDARD_RIGHTS_WRITE, FILE_WRITE_DATA, FILE_WRITE_ATTRIBUTES, FILE_WRITE_EA, and FILE_APPEND_DATA
GENERIC_EXECUTE	STANDARD_RIGHTS_EXECUTE, SYNCHRONIZE, and FILE_EXECUTE. This value is irrelevant to device and intermediate drivers.

 

The STANDARD_RIGHTS_XXX are predefined system values used to enforce security on system objects.

To open or create a directory file, as also indicated with the CreateOptions parameter, callers of NtCreateFile can specify one or a combination of the following, possibly ORed with one or more compatible flags from the preceding DesiredAccess flags list.

Value	Meaning
FILE_LIST_DIRECTORY	Files in the directory can be listed.
FILE_TRAVERSE	The directory can be traversed: that is, it can be part of the pathname of a file.

 

The FILE_READ_DATA, FILE_WRITE_DATA, FILE_EXECUTE, and FILE_APPEND_DATA DesiredAccess flags are incompatible with creating or opening a directory file.

ObjectAttributes [in]

A pointer to a structure already initialized with InitializeObjectAttributes. Members of this structure for a file object include the following.

Value	Meaning
ULONG Length	Specifies the number of bytes of ObjectAttributes data supplied. This value must be at least sizeof(OBJECT_ATTRIBUTES).
HANDLE RootDirectory	Optionally specifies a handle to a directory obtained by a preceding call to NtCreateFile. If this value is NULL, the ObjectName member must be a fully qualified file specification that includes the full path to the target file. If this value is non-NULL, the ObjectName member specifies a file name relative to this directory.
PUNICODE_STRING ObjectName	Points to a buffered Unicode string that names the file to be created or opened. This value must be a fully qualified file specification or the name of a device object, unless it is the name of a file relative to the directory specified by RootDirectory. For example, \Device\Floppy1\myfile.dat or \??\B:\myfile.dat could be the fully qualified file specification, provided that the floppy driver and overlying file system are already loaded. (Note: \?? replaces \DosDevices as the name of the object namespace. \DosDevices still works, but \?? is translated faster by the object manager.)
ULONG Attributes	Is a set of flags that controls the file object attributes. This value can be zero or OBJ_CASE_INSENSITIVE, which indicates that name-lookup code should ignore the case of the ObjectName member rather than performing an exact-match search. The value OBJ_INHERIT is irrelevant to device and intermediate drivers.
PSECURITY_DESCRIPTOR SecurityDescriptor	Optionally specifies a security descriptor to be applied to a file. ACLs specified by such a security descriptor are applied to the file only when it is created. If the value is NULL when a file is created, the ACL placed on the file is file-system-dependent; most file systems propagate some part of such an ACL from the parent directory file combined with the caller's default ACL. Device and intermediate drivers can set this member to NULL.
PSECURITY_QUALITY_OF_SERVICE SecurityQualityOfService	Specifies the access rights a server should be given to the client's security context. This value is non-NULL only when a connection to a protected server is established, allowing the caller to control which parts of the caller's security context are made available to the server and whether the server is allowed to impersonate the caller.

 

If the caller is not running in the system process context, it must set the OBJ_KERNEL_HANDLE attribute for ObjectAttributes.

IoStatusBlock [out]

A pointer to a variable that receives the final completion status and information about the requested operation. On return from NtCreateFile, the Information member contains one of the following values:

• FILE_CREATED
• FILE_OPENED
• FILE_OVERWRITTEN
• FILE_SUPERSEDED
• FILE_EXISTS
• FILE_DOES_NOT_EXIST

AllocationSize [in, optional]

The initial allocation size in bytes for the file. A nonzero value has no effect unless the file is being created, overwritten, or superseded.

FileAttributes [in]

The file attributes. Explicitly specified attributes are applied only when the file is created, superseded, or, in some cases, overwritten. By default, this value is a FILE_ATTRIBUTE_NORMAL, which can be overridden by an ORed combination of one or more FILE_ATTRIBUTE_xxxx flags, which are defined in Wdm.h and NtDdk.h. For a list of flags that can be used with NtCreateFile, see CreateFile.

ShareAccess [in]

The type of share access that the caller would like to use in the file, as zero, or as one or a combination of the following values.

Value	Meaning
FILE_SHARE_READ	The file can be opened for read access by other threads' calls to NtCreateFile.
FILE_SHARE_WRITE	The file can be opened for write access by other threads' calls to NtCreateFile.
FILE_SHARE_DELETE	The file can be opened for delete access by other threads' calls to NtCreateFile.

 

For more information, see the Windows SDK.

CreateDisposition [in]

Specifies what to do, depending on whether the file already exists, as one of the following values.

Value	Meaning
FILE_SUPERSEDE	If the file already exists, replace it with the given file. If it does not, create the given file.
FILE_CREATE	If the file already exists, fail the request and do not create or open the given file. If it does not, create the given file.
FILE_OPEN	If the file already exists, open it instead of creating a new file. If it does not, fail the request and do not create a new file.
FILE_OPEN_IF	If the file already exists, open it. If it does not, create the given file.
FILE_OVERWRITE	If the file already exists, open it and overwrite it. If it does not, fail the request.
FILE_OVERWRITE_IF	If the file already exists, open it and overwrite it. If it does not, create the given file.

 

CreateOptions [in]

The options to be applied when creating or opening the file, as a compatible combination of the following flags.

Value	Meaning
FILE_DIRECTORY_FILE	The file being created or opened is a directory file. With this flag, the CreateDisposition parameter must be set to FILE_CREATE, FILE_OPEN, or FILE_OPEN_IF. With this flag, other compatible CreateOptions flags include only the following: FILE_SYNCHRONOUS_IO_ALERT, FILE_SYNCHRONOUS_IO _NONALERT, FILE_WRITE_THROUGH, FILE_OPEN_FOR_BACKUP_INTENT, and FILE_OPEN_BY_FILE_ID.
FILE_NON_DIRECTORY_FILE	The file being opened must not be a directory file or this call fails. The file object being opened can represent a data file, a logical, virtual, or physical device, or a volume.
FILE_WRITE_THROUGH	Applications that write data to the file must actually transfer the data into the file before any requested write operation is considered complete. This flag is automatically set if the CreateOptions flag FILE_NO_INTERMEDIATE _BUFFERING is set.
FILE_SEQUENTIAL_ONLY	All accesses to the file are sequential.
FILE_RANDOM_ACCESS	Accesses to the file can be random, so no sequential read-ahead operations should be performed on the file by FSDs or the system.
FILE_NO_INTERMEDIATE_BUFFERING	The file cannot be cached or buffered in a driver's internal buffers. This flag is incompatible with the DesiredAccess FILE_APPEND_DATA flag.
FILE_SYNCHRONOUS_IO_ALERT	All operations on the file are performed synchronously. Any wait on behalf of the caller is subject to premature termination from alerts. This flag also causes the I/O system to maintain the file position context. If this flag is set, the DesiredAccess SYNCHRONIZE flag also must be set.
FILE_SYNCHRONOUS_IO_NONALERT	All operations on the file are performed synchronously. Waits in the system to synchronize I/O queuing and completion are not subject to alerts. This flag also causes the I/O system to maintain the file position context. If this flag is set, the DesiredAccess SYNCHRONIZE flag also must be set.
FILE_CREATE_TREE_CONNECTION	This flag is irrelevant to device and intermediate drivers.
FILE_COMPLETE_IF_OPLOCKED	This flag is irrelevant to device and intermediate drivers.
FILE_NO_EA_KNOWLEDGE	If the extended attributes on an existing file being opened indicate that the caller must understand EAs to properly interpret the file, fail this request because the caller does not understand how to deal with EAs. Device and intermediate drivers can ignore this flag.
FILE_DELETE_ON_CLOSE	Delete the file when the last handle to it is passed to NtClose.
FILE_OPEN_BY_FILE_ID	This flag is irrelevant to device and intermediate drivers.
FILE_OPEN_FOR_BACKUP_INTENT	This flag is irrelevant to device and intermediate drivers.

 

EaBuffer [in]

Pointer to an EA buffer used to pass extended attributes.

Note  Some file systems may not support EA buffers.

EaLength [in]

Length of the EA buffer.

Return Value

NtCreateFile returns either STATUS_SUCCESS or an appropriate error status. If it returns an error status, the caller can find more information about the cause of the failure by checking the IoStatusBlock.

Remarks

Before using this function, please read Calling Internal APIs.

The handle, given by NtCreateFile, can be used by subsequent calls to manipulate data within the file or the file object's state or attributes. For example, a driver might call this routine during initialization to open a file of microcode for its device.

There are two alternate ways to specify the name of the file to be created or opened with NtCreateFile:

• As a fully qualified pathname, supplied in the ObjectName member of the input ObjectAttributes
• As a pathname relative to the directory file represented by the handle in the RootDirectory member of the input ObjectAttributes

Certain DesiredAccess flags and combinations of flags have the following effects:

• For a caller to synchronize an I/O completion by waiting on the returned FileHandle, the SYNCHRONIZE flag must be set. Otherwise, a caller that is a device or intermediate driver must synchronize an I/O completion by using an event object.
• Passing a zero to DesiredFlags is not valid.
• If only the FILE_APPEND_DATA and SYNCHRONIZE flags are set, the caller can write only to the end of the file, and any offset information on writes to the file is ignored. However, the file is automatically extended as necessary for this type of write operation.
• Setting the FILE_WRITE_DATA flag for a file also allows writes beyond the end of the file to occur. The file is automatically extended for this type of write, as well.
• If only the FILE_EXECUTE and SYNCHRONIZE flags are set, the caller cannot directly read or write any data in the file using the returned FileHandle, that is, all operations on the file occur through the system pager in response to instruction and data accesses. Device and intermediate drivers should not set the FILE_EXECUTE flag in DesiredAccess.

The ShareAccess parameter determines whether separate threads can access the same file, possibly simultaneously. Provided that both file openers have the privilege to access a file in the specified manner, the file can be successfully opened and shared. If the original caller of NtCreateFile does not specify FILE_SHARE_READ, FILE_SHARE_WRITE, or FILE_SHARE_DELETE, no other open operations can be performed on the file; that is, the original caller is given exclusive access to the file.

For a shared file to be successfully opened, the requested DesiredAccess parameter to the file must be compatible with both the DesiredAccess and ShareAccess specifications of all preceding opens that have not yet been released with NtClose. That is, the DesiredAccess parameter specified to NtCreateFile for a given file must not conflict with the accesses that other openers of the file have disallowed.

The CreateDisposition value FILE_SUPERSEDE requires that the caller have DELETE access to an existing file object. If so, a successful call to NtCreateFile with FILE_SUPERSEDE on an existing file effectively deletes that file, and then re-creates it. This implies that, if the file has already been opened by another thread, it opened the file by specifying a ShareAccess parameter with the FILE_SHARE_DELETE flag set. Note that this type of disposition is consistent with the POSIX style of overwriting files. The CreateDisposition values FILE_OVERWRITE_IF and FILE_SUPERSEDE are similar. If ZwCreateFile is called with an existing file and either of these CreateDisposition values, the file is replaced.

Overwriting a file is semantically equivalent to a supersede operation, except for the following:

• The caller must have write access to the file, rather than delete access. This implies that, if the file has already been opened by another thread, it opened the file with the FILE_SHARE_WRITE flag set in the input ShareAccess parameter.
• The specified file attributes are logically ORed with those already on the file. This implies that, if the file has already been opened by another thread, a subsequent caller of NtCreateFile cannot disable existing FileAttributes flags but can enable additional flags for the same file. Note that this style of overwriting files is consistent with MS-DOS, Windows 3.1, and OS/2 operating systems.

The CreateOptions FILE_DIRECTORY_FILE value specifies that the file to be created or opened is a directory file. When a directory file is created, the file system creates an appropriate structure on the disk to represent an empty directory for that particular file system's on-disk structure. If this option was specified and the given file to be opened is not a directory file, or if the caller specified an inconsistent CreateOptions or CreateDisposition value, the call to NtCreateFile fails.

The CreateOptions FILE_NO_INTERMEDIATE_BUFFERING flag prevents the file system from performing any intermediate buffering on behalf of the caller. Specifying this value places certain restrictions on the caller's parameters to other NtXXXFile routines, including the following:

• Any optional ByteOffset passed to the NtReadFile or NtWriteFile function must be an integral of the sector size.
• The Length passed to NtReadFile or NtWriteFile, must be an integral of the sector size. Note that specifying a read operation to a buffer whose length is exactly the sector size might result in a lesser number of significant bytes being transferred to that buffer if the end of the file was reached during the transfer.
• Buffers must be adjusted in accordance with the alignment requirement of the underlying device. This information can be obtained by calling NtCreateFile to get a handle for the file object that represents the physical device, and then calling NtQueryInformationFile with that handle. For a list of the system FILE_XXX_ALIGNMENT values, see the Windows SDK documentation.
• Calls to NtSetInformationFile with the FileInformationClass parameter set to FilePositionInformation must specify an offset that is an integral of the sector size.

The CreateOptions FILE_SYNCHRONOUS_IO_ALERT and FILE_SYNCHRONOUS_IO_NONALERT, which are mutually exclusive as their names suggest, specify that all I/O operations on the file are to be synchronous as long as they occur through the file object referred to by the returned FileHandle. All I/O on such a file is serialized across all threads using the returned handle. With either of these CreateOptions, the DesiredAccess SYNCHRONIZE flag must be set so that the I/O Manager uses the file object as a synchronization object. With either of these CreateOptions set, the I/O Manager maintains the "file position context" for the file object, an internal, current file position offset. This offset can be used in calls to NtReadFile and NtWriteFile. Its position also can be queried or set with NtQueryInformationFile and NtSetInformationFile.

Note that the WDK header file NtDef.h is necessary for many constant definitions as well as the InitializeObjectAttributes macro. The associated import library, NtDll.lib is available in the WDK. You can also use the LoadLibrary and GetProcAddress functions to dynamically link to NtDll.dll.

Requirements

Build date: 7/9/2009