Module libvirt-event from libvirt

Provides APIs for the management of events

Table of Contents

Types

typedef enum virEventHandleType

Functions

int	virEventAddHandle		(int fd, 
int events,
virEventHandleCallback cb,
void * opaque,
virFreeCallback ff) typedef virEventAddHandleFunc int virEventAddHandleFunc (int fd,
int event,
virEventHandleCallback cb,
void * opaque,
virFreeCallback ff) int virEventAddTimeout (int timeout,
virEventTimeoutCallback cb,
void * opaque,
virFreeCallback ff) typedef virEventAddTimeoutFunc int virEventAddTimeoutFunc (int timeout,
virEventTimeoutCallback cb,
void * opaque,
virFreeCallback ff) typedef virEventHandleCallback void virEventHandleCallback (int watch,
int fd,
int events,
void * opaque) int virEventRegisterDefaultImpl (void) void virEventRegisterImpl (virEventAddHandleFunc addHandle,
virEventUpdateHandleFunc updateHandle,
virEventRemoveHandleFunc removeHandle,
virEventAddTimeoutFunc addTimeout,
virEventUpdateTimeoutFunc updateTimeout,
virEventRemoveTimeoutFunc removeTimeout) int virEventRemoveHandle (int watch) typedef virEventRemoveHandleFunc int virEventRemoveHandleFunc (int watch) int virEventRemoveTimeout (int timer) typedef virEventRemoveTimeoutFunc int virEventRemoveTimeoutFunc (int timer) int virEventRunDefaultImpl (void) typedef virEventTimeoutCallback void virEventTimeoutCallback (int timer,
void * opaque) void virEventUpdateHandle (int watch,
int events) typedef virEventUpdateHandleFunc void virEventUpdateHandleFunc (int watch,
int event) void virEventUpdateTimeout (int timer,
int timeout) typedef virEventUpdateTimeoutFunc void virEventUpdateTimeoutFunc (int timer,
int timeout)

Description

Types

virEventHandleType

Functions

virEventAddHandle

int	virEventAddHandle		(int fd,
					 int events,
					 virEventHandleCallback cb,
					 void * opaque,
					 virFreeCallback ff)

Register a callback for monitoring file handle events. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

fd
file handle to monitor for events
events
bitset of events to watch from virEventHandleType constants
cb
callback to invoke when an event occurs
opaque
user data to pass to callback
ff
callback to free opaque when handle is removed
Returns
-1 if the file handle cannot be registered, otherwise a handle watch number to be used for updating and unregistering for events.

virEventAddHandleFunc

typedef int	(*virEventAddHandleFunc	)	(int fd,
					 int event,
					 virEventHandleCallback cb,
					 void * opaque,
					 virFreeCallback ff)

Part of the EventImpl, this callback adds a file handle callback to listen for specific events. The same file handle can be registered multiple times provided the requested event sets are non-overlapping

If the opaque user data requires free'ing when the handle is unregistered, then a 2nd callback can be supplied for this purpose. This callback needs to be invoked from a clean stack. If 'ff' callbacks are invoked directly from the virEventRemoveHandleFunc they will likely deadlock in libvirt.

fd
file descriptor to listen on
event
bitset of events on which to fire the callback
cb
the callback to be called when an event occurrs
opaque
user data to pass to the callback
ff
the callback invoked to free opaque data blob
Returns
-1 if the file handle cannot be registered, otherwise a handle watch number to be used for updating and unregistering for events

virEventAddTimeout

int	virEventAddTimeout		(int timeout,
					 virEventTimeoutCallback cb,
					 void * opaque,
					 virFreeCallback ff)

Register a callback for a timer event. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

Setting @timeout to -1 will disable the timer. Setting @timeout to zero will cause it to fire on every event loop iteration.

timeout
time between events in milliseconds
cb
callback to invoke when an event occurs
opaque
user data to pass to callback
ff
callback to free opaque when timeout is removed
Returns
-1 if the timer cannot be registered, a positive integer timer id upon success.

virEventAddTimeoutFunc

typedef int	(*virEventAddTimeoutFunc	)	(int timeout,
					 virEventTimeoutCallback cb,
					 void * opaque,
					 virFreeCallback ff)

Part of the EventImpl, this user-defined callback handles adding an event timeout.

If the opaque user data requires free'ing when the handle is unregistered, then a 2nd callback can be supplied for this purpose.

timeout
The timeout to monitor
cb
the callback to call when timeout has expired
opaque
user data to pass to the callback
ff
the callback invoked to free opaque data blob
Returns
a timer value

virEventHandleCallback

typedef void	(*virEventHandleCallback	)	(int watch,
					 int fd,
					 int events,
					 void * opaque)

Callback for receiving file handle events. The callback will be invoked once for each event which is pending.

watch
watch on which the event occurred
fd
file handle on which the event occurred
events
bitset of events from virEventHandleType constants
opaque
user data registered with handle

virEventRegisterDefaultImpl

int	virEventRegisterDefaultImpl	(void)

Registers a default event implementation based on the poll() system call. This is a generic implementation that can be used by any client application which does not have a need to integrate with an external event loop impl.

For proper event handling, it is important that the event implementation is registered before a connection to the Hypervisor is opened.

Once registered, the application has to invoke virEventRunDefaultImpl() in a loop to process events. Failure to do so may result in connections being closed unexpectedly as a result of keepalive timeout. The default event loop fully supports handle and timeout events, but only wakes up on events registered by libvirt API calls such as virEventAddHandle() or virConnectDomainEventRegisterAny().

Returns
0 on success, -1 on failure.

virEventRegisterImpl

void	virEventRegisterImpl		(virEventAddHandleFunc addHandle,
					 virEventUpdateHandleFunc updateHandle,
					 virEventRemoveHandleFunc removeHandle,
					 virEventAddTimeoutFunc addTimeout,
					 virEventUpdateTimeoutFunc updateTimeout,
					 virEventRemoveTimeoutFunc removeTimeout)

Registers an event implementation, to allow integration with an external event loop. Applications would use this to integrate with the libglib2 event loop, or libevent or the QT event loop.

For proper event handling, it is important that the event implementation is registered before a connection to the Hypervisor is opened.

Use of the virEventAddHandle() and similar APIs require that the corresponding handler is registered. Use of the virConnectDomainEventRegisterAny() and similar APIs requires that the three timeout handlers are registered. Likewise, the three timeout handlers must be registered if the remote server has been configured to send keepalive messages, or if the client intends to call virConnectSetKeepAlive(), to avoid either side from unexpectedly closing the connection due to inactivity.

If an application does not need to integrate with an existing event loop implementation, then the virEventRegisterDefaultImpl() method can be used to setup the generic libvirt implementation.

Once registered, the event loop implementation cannot be changed, and must be run continuously. Note that callbacks may remain registered for a short time even after calling virConnectClose on all open connections, so it is not safe to stop running the event loop immediately after closing the connection.

addHandle
the callback to add fd handles
updateHandle
the callback to update fd handles
removeHandle
the callback to remove fd handles
addTimeout
the callback to add a timeout
updateTimeout
the callback to update a timeout
removeTimeout
the callback to remove a timeout

virEventRemoveHandle

int	virEventRemoveHandle		(int watch)

Unregister a callback from a file handle. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

watch
watch whose file handle to remove
Returns
-1 if the file handle was not registered, 0 upon success.

virEventRemoveHandleFunc

typedef int	(*virEventRemoveHandleFunc)	(int watch)

Part of the EventImpl, this user-provided callback is notified when an fd is no longer being listened on.

If a virEventHandleFreeFunc was supplied when the handle was registered, it will be invoked some time during, or after this function call, when it is safe to release the user data.

watch
file descriptor watch to stop listening on
Returns
-1 if the file handle was not registered, 0 upon success

virEventRemoveTimeout

int	virEventRemoveTimeout		(int timer)

Unregister a callback for a timer. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

timer
the timer id to remove
Returns
-1 if the timer was not registered, 0 upon success.

virEventRemoveTimeoutFunc

typedef int	(*virEventRemoveTimeoutFunc)	(int timer)

Part of the EventImpl, this user-defined callback removes a timer

If a virEventTimeoutFreeFunc was supplied when the handle was registered, it will be invoked some time during, or after this function call, when it is safe to release the user data.

timer
the timer to remove
Returns
0 on success, -1 on failure

virEventRunDefaultImpl

int	virEventRunDefaultImpl		(void)

Run one iteration of the event loop. Applications will generally want to have a thread which invokes this method in an infinite loop. Furthermore, it is wise to set up a pipe-to-self handler (via virEventAddHandle()) or a timeout (via virEventAddTimeout()) before calling this function, as it will block forever if there are no registered events.

static bool quit;

while (!quit) {
  if (virEventRunDefaultImpl() < 0)
    ...print error...
}
Returns
0 on success, -1 on failure.

virEventTimeoutCallback

typedef void	(*virEventTimeoutCallback	)	(int timer,
					 void * opaque)

callback for receiving timer events

timer
timer id emitting the event
opaque
user data registered with handle

virEventUpdateHandle

void	virEventUpdateHandle		(int watch,
					 int events)

Change event set for a monitored file handle. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

Will not fail if fd exists.

watch
watch whose file handle to update
events
bitset of events to watch from virEventHandleType constants

virEventUpdateHandleFunc

typedef void	(*virEventUpdateHandleFunc)	(int watch,
					 int event)

Part of the EventImpl, this user-provided callback is notified when events to listen on change

watch
file descriptor watch to modify
event
new events to listen on

virEventUpdateTimeout

void	virEventUpdateTimeout		(int timer,
					 int timeout)

Change frequency for a timer. This function requires that an event loop has previously been registered with virEventRegisterImpl() or virEventRegisterDefaultImpl().

Setting frequency to -1 will disable the timer. Setting the frequency to zero will cause it to fire on every event loop iteration.

Will not fail if timer exists.

timer
timer id to change
timeout
time between events in milliseconds

virEventUpdateTimeoutFunc

typedef void	(*virEventUpdateTimeoutFunc)	(int timer,
					 int timeout)

Part of the EventImpl, this user-defined callback updates an event timeout.

timer
the timer to modify
timeout
the new timeout value