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.Dd September 15, 2024
.Dt DDI_ADD_EVENT_HANDLER 9F
.Os
.Sh NAME
.Nm ddi_add_event_handler
.Nd add an NDI event service callback handler
.Sh SYNOPSIS
.In sys/dditypes.h
.In sys/sunddi.h
.Ft int
.Fo ddi_add_event_handler
.Fa "dev_info_t *dip"
.Fa "ddi_eventcookie_t cookie"
.Fa "void (*handler)(dev_info_t *dip, ddi_eventcookie_t cookie, void *arg, void *bus)"
.Fa "void *arg"
.Fa "ddi_callback_id_t *id"
.Fc
.Sh INTERFACE LEVEL
illumos DDI specific
.Pq illumos DDI .
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa dip
Device node registering the callback.
.It Fa cookie
Cookie returned from call to
.Xr ddi_get_eventcookie 9F .
.It Fa handler
Callback handler responsible for handling an NDI event service notification.
Its first
.Vt "void *"
argument corresponds to
.Fa arg .
The second is bus-specific data.
.It Fa arg
Pointer to opaque data supplied by the caller.
Typically, this would be a pointer to the driver's softstate structure.
.It Fa id
Pointer to a callback ID.
The callback ID will be filled in when this function is called and serves as a
unique identifier for this particular event handler.
This ID must be saved so it can be used in a later call to
.Xr ddi_remove_event_handler 9F
to remove the callback.
.El
.Sh DESCRIPTION
The
.Fn ddi_add_event_handler
function adds a callback handler to be invoked in the face of the event
specified by
.Fa cookie .
The process of adding a callback handler is also known as subscribing to an
event.
Upon successful subscription, the handler will be invoked by the system when the
event occurs.
The handler can be unregistered by using
.Xr ddi_remove_event_handler 9F .
.Pp
An instance of a driver can register multiple handlers for an event or a single
handler for multiple events.
Callback order is not defined and should assumed to be random.
.Pp
The callback.
.Fa handler
will be invoked with the following arguments:
.Bl -tag -width Fa
.It Fa "dev_info_t *dip"
Device node requesting the notification.
.It Fa "ddi_eventcookie_t cookie"
Structure describing event that occurred.
.It Fa "void *arg"
Opaque data pointer provided, by the driver, during callback registration.
.It Fa "void *bus"
Pointer to event specific data defined by the framework which invokes the
callback function.
.El
.Sh CONTEXT
The
.Fn ddi_add_event_handler
and
.Fn handler
function can be called from user and kernel contexts only.
.Sh RETURN VALUES
Upon successful completion,
the
.Fn ddi_add_event_handler
function returns
.Dv DDI_SUCCESS
and the callback handler is successfully registered.
Otherwise,
.Dv DDI_FAILURE
is returned and the callback handler failed to register.
Possible reasons include lack of resources or a bad cookie.
.Sh INTERFACE STABILITY
.Sy Committed
.Sh SEE ALSO
.Xr attributes 7 ,
.Xr ddi_get_eventcookie 9F ,
.Xr ddi_remove_event_handler 9F
.Rs
.%T Writing Device Drivers
.Re
.Sh NOTES
Drivers must remove all registered callback handlers for a device instance by
calling
.Xr ddi_remove_event_handler 9F
before
.Xr detach 9E
completes.