ZwOpenEvent function

The ZwOpenEvent routine opens a handle to an existing named event object with the specified desired access.

Syntax

NTSYSCALLAPI NTSTATUS ZwOpenEvent(
  PHANDLE            EventHandle,
  ACCESS_MASK        DesiredAccess,
  POBJECT_ATTRIBUTES ObjectAttributes
);

Parameters

EventHandle

A pointer to a variable that will receive the event object handle. The handle includes bookkeeping information, such as a reference count and security context.

DesiredAccess

The ACCESS_MASK value that represents the desired types of access for the event object. The following table contains the event-specific ACCESS_MASK values.

Value Desired access
EVENT_QUERY_STATE Query the state of the event object.
EVENT_MODIFY_STATE Modify the state of the event object.
EVENT_ALL_ACCESS All possible access rights to the event object.

ObjectAttributes

A pointer to the object attributes structure that the caller supplied to be used for the specified object. These attributes would include the ObjectName and the handle attributes, for example. This parameter is initialized by calling the InitializeObjectAttributes macro.

Return Value

ZwOpenEvent returns STATUS_SUCCESS or an appropriate error status. This routine might return one of the following error status codes:

Return code Description
STATUS_INSUFFICIENT_RESOURCES
Resources that this function requires could not be allocated.
STATUS_INVALID_PARAMETER
The ObjectAttributes structure was not supplied or contained an invalid parameter value.
STATUS_OBJECT_NAME_INVALID
The ObjectAttributes parameter contained an ObjectName in the OBJECT_ATTRIBUTES structure that was invalid.
STATUS_OBJECT_PATH_SYNTAX_BAD
The object path contained incorrect syntax. For example, the ObjectAttributes parameter does not contain a RootDirectory member, but the ObjectName member in the OBJECT_ATTRIBUTES structure is an empty string or does not start with an OBJECT_NAME_PATH_SEPARATOR character.
STATUS_OBJECT_PATH_NOT_FOUND
The path to the object was not found, indicating that it does not exist.
STATUS_OBJECT_NAME_NOT_FOUND
The object name was not found, indicating that the object does not exist.
STATUS_PRIVILEGE_NOT_HELD
The caller did not have the required privilege to create a handle with the access specified in the DesiredAccess parameter.

Remarks

ZwOpenEvent opens an existing named event object and creates a handle to the object with the specified desired access.

ZwOpenEvent can open either notification or synchronization events.

Events are used to coordinate execution. File system drivers can use events to enable a caller to wait for completion of the requested operation until the given event is set to the Signaled state.

Notification events can be used to notify one or more threads of execution that an event has occurred. Synchonization events can be used in the serialization of access to hardware between two otherwise unrelated drivers.

Note  If the call to the ZwOpenEvent function occurs in user mode, you should use the name "NtOpenEvent" instead of "ZwOpenEvent".
 
For calls from kernel-mode drivers, the NtXxx and ZwXxx versions of a Windows Native System Services routine can behave differently in the way that they handle and interpret input parameters. For more information about the relationship between the NtXxx and ZwXxx versions of a routine, see Using Nt and Zw Versions of the Native System Services Routines.

Requirements

   
Minimum supported client Available starting with Windows Server 2003.
Target Platform Universal
Header wdm.h (include Wdm.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe
IRQL PASSIVE_LEVEL
DDI compliance rules PowerIrpDDis, HwStorPortProhibitedDDIs

See Also

ACCESS_MASK

InitializeObjectAttributes

IoCreateNotificationEvent

IoCreateSynchronizationEvent

KeClearEvent

KeResetEvent

KeSetEvent

KeWaitForSingleObject

Using Nt and Zw Versions of the Native System Services Routines

ZwClose

ZwCreateEvent

ZwSetEvent

ZwWaitForSingleObject