Re: [libvirt] [PATCH] event: improve public API docs

Since libvirt 0.9.3, the entire virevent.c file has been a public API, so improve the documentation in this file. Also, fix a potential core dump - it could only be triggered by bogus use of the API and would only affect the caller (not libvirtd), but we might as well be nice. * src/libvirt.c (virConnectDomainEventRegister) (virConnectDomainEventRegisterAny) (virConnectNetworkEventRegisterAny): Document event loop requirement. * src/util/virevent.c (virEventAddHandle, virEventRemoveHandle) (virEventAddTimeout, virEventRemoveTimeout): Likewise. (virEventUpdateHandle, virEventUpdateTimeout): Likewise, and avoid core dump if caller didn't register handler. (virEventRunDefaultImpl): Expand example, and set up code block in html docs. (virEventRegisterImpl, virEventRegisterDefaultImpl): Document more on the use of the event loop. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- src/libvirt.c | 24 ++++++++++------ src/util/virevent.c | 82 +++++++++++++++++++++++++++++++++++------------------ 2 files changed, 70 insertions(+), 36 deletions(-) diff --git a/src/libvirt.c b/src/libvirt.c index 66841c8..f43718d 100644 --- a/src/libvirt.c +++ b/src/libvirt.c @@ -16121,11 +16121,13 @@ error: * @freecb: optional function to deallocate opaque when not used anymore * * Adds a callback to receive notifications of domain lifecycle events - * occurring on a connection + * occurring on a connection. This function requires that an event loop + * has been previously registered with virEventRegisterImpl() or + * virEventRegisterDefaultImpl(). * * Use of this method is no longer recommended. Instead applications * should try virConnectDomainEventRegisterAny() which has a more flexible - * API contract + * API contract. * * The virDomainPtr object handle passed into the callback upon delivery * of an event is only valid for the duration of execution of the callback. @@ -16134,7 +16136,7 @@ error: * The reference can be released once the object is no longer required * by calling virDomainFree. * - * Returns 0 on success, -1 on failure + * Returns 0 on success, -1 on failure. */ int virConnectDomainEventRegister(virConnectPtr conn, @@ -19064,10 +19066,12 @@ error: * @freecb: optional function to deallocate opaque when not used anymore * * Adds a callback to receive notifications of arbitrary domain events - * occurring on a domain. + * occurring on a domain. This function requires that an event loop + * has been previously registered with virEventRegisterImpl() or + * virEventRegisterDefaultImpl(). * * If @dom is NULL, then events will be monitored for any domain. If @dom - * is non-NULL, then only the specific domain will be monitored + * is non-NULL, then only the specific domain will be monitored. * * Most types of event have a callback providing a custom set of parameters * for the event. When registering an event, it is thus necessary to use @@ -19085,7 +19089,7 @@ error: * for the callback. To unregister a callback, this callback ID should * be passed to the virConnectDomainEventDeregisterAny() method. * - * Returns a callback identifier on success, -1 on failure + * Returns a callback identifier on success, -1 on failure. */ int virConnectDomainEventRegisterAny(virConnectPtr conn, @@ -19183,10 +19187,12 @@ error: * @freecb: optional function to deallocate opaque when not used anymore * * Adds a callback to receive notifications of arbitrary network events - * occurring on a network. + * occurring on a network. This function requires that an event loop + * has been previously registered with virEventRegisterImpl() or + * virEventRegisterDefaultImpl(). * * If @net is NULL, then events will be monitored for any network. If @net - * is non-NULL, then only the specific network will be monitored + * is non-NULL, then only the specific network will be monitored. * * Most types of event have a callback providing a custom set of parameters * for the event. When registering an event, it is thus necessary to use @@ -19204,7 +19210,7 @@ error: * for the callback. To unregister a callback, this callback ID should * be passed to the virConnectNetworkEventDeregisterAny() method. * - * Returns a callback identifier on success, -1 on failure + * Returns a callback identifier on success, -1 on failure. */ int virConnectNetworkEventRegisterAny(virConnectPtr conn, diff --git a/src/util/virevent.c b/src/util/virevent.c index fde29a2..0c94946 100644 --- a/src/util/virevent.c +++ b/src/util/virevent.c @@ -37,6 +37,16 @@ static virEventAddTimeoutFunc addTimeoutImpl = NULL; static virEventUpdateTimeoutFunc updateTimeoutImpl = NULL; static virEventRemoveTimeoutFunc removeTimeoutImpl = NULL; + +/***************************************************** + * + * Below this point are *PUBLIC* APIs for event + * loop integration with applications using libvirt. + * These API contracts cannot be changed. + * + *****************************************************/ + + /** * virEventAddHandle: * @@ -46,10 +56,12 @@ static virEventRemoveTimeoutFunc removeTimeoutImpl = NULL; * @opaque: user data to pass to callback * @ff: callback to free opaque when handle is removed * - * Register a callback for monitoring file handle events. + * Register a callback for monitoring file handle events. This function + * requires that an event loop has previously been registered with + * virEventRegisterImpl() or virEventRegisterDefaultImpl(). * * Returns -1 if the file handle cannot be registered, otherwise a handle - * watch number to be used for updating and unregistering for events + * watch number to be used for updating and unregistering for events. */ int virEventAddHandle(int fd, @@ -70,14 +82,17 @@ virEventAddHandle(int fd, * @watch: watch whose file handle to update * @events: bitset of events to watch from virEventHandleType constants * - * Change event set for a monitored file handle. + * 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 + * Will not fail if fd exists. */ void virEventUpdateHandle(int watch, int events) { - updateHandleImpl(watch, events); + if (updateHandleImpl) + updateHandleImpl(watch, events); } /** @@ -85,7 +100,9 @@ virEventUpdateHandle(int watch, int events) * * @watch: watch whose file handle to remove * - * Unregister a callback from a file handle. + * Unregister a callback from a file handle. This function + * requires that an event loop has previously been registered with + * virEventRegisterImpl() or virEventRegisterDefaultImpl(). * * Returns -1 if the file handle was not registered, 0 upon success. */ @@ -106,7 +123,9 @@ virEventRemoveHandle(int watch) * @opaque: user data to pass to callback * @ff: callback to free opaque when timeout is removed * - * Register a callback for a timer event. + * 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 the timeout * to zero will cause it to fire on every event loop iteration. @@ -132,17 +151,20 @@ virEventAddTimeout(int timeout, * @timer: timer id to change * @timeout: time between events in milliseconds * - * Change frequency for a timer. + * 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 + * Will not fail if timer exists. */ void virEventUpdateTimeout(int timer, int timeout) { - updateTimeoutImpl(timer, timeout); + if (updateTimeoutImpl) + updateTimeoutImpl(timer, timeout); } /** @@ -150,7 +172,9 @@ virEventUpdateTimeout(int timer, int timeout) * * @timer: the timer id to remove * - * Unregister a callback for a timer. + * Unregister a callback for a timer. This function + * requires that an event loop has previously been registered with + * virEventRegisterImpl() or virEventRegisterDefaultImpl(). * * Returns -1 if the timer was not registered, 0 upon success. */ @@ -164,14 +188,6 @@ virEventRemoveTimeout(int timer) } -/***************************************************** - * - * Below this point are 3 *PUBLIC* APIs for event - * loop integration with applications using libvirt. - * These API contracts cannot be changed. - * - *****************************************************/ - /** * virEventRegisterImpl: * @addHandle: the callback to add fd handles @@ -186,9 +202,14 @@ virEventRemoveTimeout(int timer) * to integrate with the libglib2 event loop, or libevent * or the QT event loop. * + * Use of the virEventAddHandle() and similar APIs require that the + * corresponding handler be registered. Use of the + * virConnectDomainEventRegisterAny() and similar APIs requires that + * the three timeout handlers be registered.

+ * * If an application does not need to integrate with an * existing event loop implementation, then the - * virEventRegisterDefaultImpl method can be used to setup + * virEventRegisterDefaultImpl() method can be used to setup * the generic libvirt implementation. */ void virEventRegisterImpl(virEventAddHandleFunc addHandle, @@ -220,9 +241,12 @@ void virEventRegisterImpl(virEventAddHandleFunc addHandle, * not have a need to integrate with an external event * loop impl. * - * Once registered, the application has to invoke virEventRunDefaultImpl in + * 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. + * closed unexpectedly as a result of keepalive timeout. The default + * event loop fully supports handle and 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. */ @@ -255,14 +279,18 @@ int virEventRegisterDefaultImpl(void) * * Run one iteration of the event loop. Applications * will generally want to have a thread which invokes - * this method in an infinite loop + * 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 = false; + * static bool quit = false; * - * while (!quit) { - * if (virEventRunDefaultImpl() < 0) + * while (!quit) { + * if (virEventRunDefaultImpl() < 0) * ...print error... - * } + * } * * Returns 0 on success, -1 on failure. */ -- 1.8.4.2