Tribblix: manual page: ldi_ev_register

LDI_EV_REGISTER_CALLBACKS(9F) Kernel Functions for Drivers

NAME

ldi_ev_register_callbacks - add a notify and/or finalize callback

SYNOPSIS

#include <sys/sunldi.h>

int ldi_ev_register_callbacks(ldi_handle_t lh,
ldi_ev_cookie_t *cookie, ldi_ev_callback_t *callb,
void *arg, ldi_callback_id_t *id);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

ldi_handle_t lh

A layered handle representing the device for which the event
notification was requested.

ldi_ev_cookie_t *cookie

An opaque event cookie for the event type returned by a previous
call to ldi_ev_get_cookie(9F).

ldi_ev_callback_t *callb

A data structure which currently has the following members:

struct ldi_ev_callback {
uint_t cb_vers;
int (*cb_notify)(ldi_handle_t,
ldi_ev_cookie_t cookie,
void *arg, void *ev_data);
void (*cb_finalize)(ldi_handle_t,
ldi_ev_cookie_t cookie,
int ldi_result,
void *arg,
void *ev_data);
} ldi_ev_callback_t;

where

cb_vers
Version of callback vector. Must be set to
LDI_EV_CB_VERS by the caller.

The arguments passed into the callbacks when they are
invoked, include:

int ldi_result

The actual result of the state change
operation/event passed to finalize callback:
LDI_EV_SUCCESS: The state change succeeded
LDI_EV_FAILURE: The state change failed.

void *ev_data

Event specific data.

void *arg

A pointer to opaque caller private data.

ldi_callback_id_t *id

Unique system wide registration id returned by
ldi_ev_register_callbacks(9F) upon successful registration.

DESCRIPTION

The ldi_ev_register_callbacks() interface allows layered drivers to
register notify and finalize callbacks for certain events. These
events are listed in the ldi_ev_get_cookie(9F) man page. The notify
callback is invoked only for events that can be blocked, just before
the event occurs. The notify event is not called for events serviced
by the NDI event service framework since such events are by
definition asynchronous. Only the finalize callback is invoked for
such events. Layered drivers that have registered notify callbacks
for that event have the opportunity of blocking such events. The
finalize callback is invoked once the final disposition of the state
of a device (specifically a device minor node) is known. The callback
is invoked with this result, either LDI_EV_SUCCESS (state change
succeeded) or LDI_EV_FAILURE (state change failed). This allows
layered driver consumers to finalize any changes they made in
response to a previous "notify" callback.

For example, a layered driver's notify callback may be invoked in
response to a LDI_EV_OFFLINE event. The layered driver may
reconfigure itself to stop using the device and permit the change to
go forward. Once that happens, the I/O framework attempts to actually
take the device offline. This offline attempt can have two possible
outcomes: success or failure. In the former case, the finalize
callback is invoked with the ldi_result argument set to
LDI_EV_SUCCESS and the layered driver knows that the device has been
taken offline. In the latter case, finalize is invoked with the
ldi_result set to LDI_EV_FAILURE and the layered driver knows that
the state change failed. In this case, it may choose to reconfigure
itself to start using the device again.

Finalize callbacks can be registered for all events including events
that cannot be blocked.

A layered driver can also propagate these events up the software
stack by using interfaces offered by the LDI event framework. The
layered driver may use ldi_ev_notify() to propagate notify events
occurring on minors it imports onto minors it exports. Similarly, it
may use ldi_ev_finalize() to propagate finalize events. Both
ldi_ev_notify() and ldi_ev_finalize() propagate events to device
contracts as well as LDI callbacks registered against the exported
minor nodes.

The LDI event framework has the following guarantees and requirements
with respect to these callbacks:

1. The notify() callback is invoked before an event
(represented by the event cookie) occurs on a device
(represented by the layered driver handle) and is invoked
only for events that can be blocked. If the callback
returns LDI_EV_FAILURE, the event is blocked. If the
callback returns LDI_EV_SUCCESS, the event is allowed to
proceed. If any other value is returned, it is an error.
An error message is logged and the event is blocked. An
example of an event that can be blocked and for which
notify callbacks may be invoked is the offline event
LDI_EV_OFFLINE.

2. The finalize callback is invoked for all events (including
events that cannot be blocked) after the event has
occurred. It is invoked with either LDI_EV_SUCCESS
indicating that the event successfully happened or
LDI_EV_FAILURE indicating that the event did not occur.
The finalize callback returns no values. Good examples of
events that cannot be blocked are the degrade event
(LDI_EV_DEGRADE) and events serviced by the NDI event
service framework.

3. Layered drivers may register one or both of these
callbacks (that is, only for a notify event or only for a
finalize event or for both) against any LDI handle that
they may possess. If a finalize or notify event is not
being registered, the corresponding pointer in the
ldi_ev_callback_t structure must be set to NULL. It is an
error to attempt a registration with both callbacks set to
NULL.

4. A notify and/or finalize callback is invoked only if the
corresponding LDI handle is open. If an LDI handle against
which the callbacks are registered is closed, the
corresponding finalize and notify callbacks is not invoked
as it is assumed that the layered driver is no longer
interested in the device. See number 5 below for the
exception to this rule.

5. A layered driver that closes its LDI handle in its notify
routine receives the corresponding finalize callback after
the event has occurred. Because the LDI handle has been
closed, the finalize callback is invoked with a NULL LDI
handle. It is the responsibility of the layered driver to
maintain state in its private "arg" parameter so that it
can reopen the device (if desired) in its finalize
callback.

One example where this may happen is with the
LDI_EV_OFFLINE event. A layered driver's notify callback
may be invoked for an offline event. The layered driver
may choose to allow this event to proceed. In that case,
since it has a layered open of the device, it must close
the LDI handle so that the offline event can succeed (an
offline of a device does not succeed if there is any open
of the device, layered or otherwise). Since the layered
driver has closed the LDI handle in the notify routine,
its finalize callback (if any) is invoked with a NULL LDI
handle. It is the responsibility of the layered driver to
maintain state (such as the device path or devid) in its
private "arg" parameter, so that in the finalize routine,
it can do a layered open of the device if the device
offline failed.

This is the only exception where the finalize callback is
invoked if the LDI handle has been closed. In all other
cases if the LDI handle has been closed, no corresponding
callbacks is invoked.

6. In order for the offline event to succeed
(LDI_EV_OFFLINE), it is imperative that there be no opens
(including LDI handles) to the device. If a layered
driver's notify callback is invoked for an offline event
and the driver intends to allow the offline to proceed,
the driver must close the corresponding LDI handle.

7. The notify and finalize callbacks are not automatically
unregistered even if the corresponding LDI handle has been
closed. It is the responsibility of the layered driver to
unregister these callbacks when they are not required. It
may do so using the ldi_ev_remove_callbacks(9F) interface.
The LDI framework may panic if the entity registering the
callback (such as a dip, dev_t or module) no longer exists
on the system and the corresponding callbacks have not
been unregistered.

8. The LDI event framework guarantees that if a layered
driver receives a notify event, it also receives a
finalize event except if the layered consumer itself
blocked the event (that is, it returned LDI_EV_FAILURE
from its notify callback. In this case, the layered driver
knows that the event has been blocked and therefore does
not need the finalize callback.

9. If a layered driver propagates notify events on minors it
imports to minors it exports, it must first propagate
these events up the software stack via ldi_eve_notify() in
its notify callback. It must do so before attempting to
check if it blocks the event. This is required, because a
layered driver cannot release the device if consumers up
the stack are still using the device. If ldi_ev_notify()
returns LDI_EV_FAILURE, the callback must immediately
return LDI_EV_FAILURE from its notify callback. If
ldi_ev_notify() returns LDI_EV_SUCCESS, then the state
change is permissible as far as consumers higher up in the
software stack are concerned. The layered driver must
then determine if it can permit the state change. If the
state change is to be allowed, the layered driver must
return LDI_EV_SUCCESS. If the layered driver determines
that the state change should not be permitted, it must
invoke ldi_ev_finalize() on minors it exports with a
result of LDI_EV_FAILURE (to inform consumers up the
stack) and then return LDI_EV_FAILURE from its notify
callback.

10. The LDI event framework generates finalize events at the
earliest point where a failure is detected. If the failure
is detected in the framework (such as in ldi_ev_notify())
the framework generates the finalize events. In the event
that a failure is first detected in a layered driver (that
is, in the notify callback of a layered driver) the
layered driver must use ldi_ev_finalize() to send
finalize events up the software stack. See the examples
for code snippets describing this scenario.

11. The finalize callback must first reconfigure itself before
attempting to propagate the event up the software stack
via ldi_ev_finalize(9F). This is so that the minors it
exports are available and ready for use before the
finalize event is propagated up the software stack.

12. It may so happen that the event propagated up the software
stack is not the same as the event for which a layered
driver's notify/finalize callback is invoked. For example,
a layered driver's callback(s) may be invoked for an
offline event, but the driver may choose to only propagate
the degraded event to its consumers (since it may have a
mirror/copy of the data on the device.) In that case, the
layered driver must generate a different event cookie
(that is, one corresponding to the degraded event via
ldi_ev_get_cookie(9F)) and use that cookie in its
propagation calls (that is, ldi_ev_notify(9F) and
ldi_ev_finalize(9F)).

Once the registration of the callback(s) is successful, an opaque
ldi_callback_id_t structure is returned which may be used to
unregister the callback(s) later.

RETURN VALUES

The return values for this function are:

LDI_EV_SUCCESS

Callback(s) added successfully.

LDI_EV_FAILURE

Failed to add callback(s).

CONTEXT

This function can be called from user and kernel contexts only.

EXAMPLES

Example 1: Registration and Callbacks for the OFFLINE Event

The following example shows how the ldi_ev_register_callbacks()
function performs a registration and callback for the offline event:

static int
event_register(void)
{
ldi_handle_t lh;
ldi_ev_callback_t callb;
ldi_ev_cookie_t off_cookie;

if (ldi_ev_get_cookie(lh, LDI_EV_OFFLINE, &off_cookie)
== LDI_EV_FAILURE)
goto fail;

callb.cb_vers = LDI_EV_CB_VERS;
callb.cb_notify = off_notify;
callb.cb_finalize = off_finalize;

if (ldi_ev_register_callbacks(lh, off_cookie, &callb, arg, &id)
!= LDI_EV_SUCCESS)
goto fail;
}

static void
event_unregister(ldi_callback_id_t id)
{
ldi_ev_remove_callbacks(id);
}

static int
off_notify(ldi_handle_t lh, ldi_ev_cookie_t off_cookie, void *arg,
void *ev_data)
{

ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_OFFLINE) == 0);

/* Map imported minors to exported minor */
widget_map(lh, &minor, &spec_type);

/*
* Call ldi_ev_notify() to propagate events to our consumers.
* This *must* happen before we check if offline should be blocked
*/
if (ldi_ev_notify(dip, minor, spec_type, off_cookie, ev_data)
!= LDI_EV_SUCCESS)
return (LDI_EV_FAILURE);

/*
* Next, check if we can allow the offline
*/
if (widget_check(lh) == WIDGET_SUCCESS) {
widget_save_path(arg, lh);
widget_reconfigure(lh, RELEASE);
ldi_close(lh);
return (LDI_EV_SUCCESS)
}

/*
* We cannot permit the offline. The first layer that detects
* failure i.e. us, must generate finalize events for our
consumers
*/
ldi_ev_finalize(dip, minor, spec_type, LDI_EV_FAILURE, off_cookie,
ev_data);

return (LDI_EV_FAILURE);
}

/*
/*
* The finalize callback will only be called if we returned LDI_EV_SUCCESS
* in our notify callback. ldi_result passed in may be SUCCESS or FAILURE
*/
static void
off_finalize(ldi_handle_t NULL_lh, ldi_ev_cookie_t off_cookie,
int ldi_result, void *arg, void *ev_data)
{
ldi_handle_t lh;

ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_OFFLINE) == 0);

path = widget_get_path(arg);

widget_map_by_path(path, &minor, &spec_type);

if (ldi_result == LDI_EV_SUCCESS) {
ldi_ev_finalize(dip, minor, spec_type, LDI_EV_SUCCESS,
off_cookie, ev_data);
return;
}

/* The offline failed. Reopen the device */
ldi_open_by_name(path, &lh);
widget_reconfigure(lh, REACQUIRE);

ldi_ev_finalize(dip, minor, spec_type, LDI_EV_FAILURE, off_cookie,
ev_data);
}

Example 2: Registration and Callbacks for the DEGRADE Event

The following example shows how the ldi_ev_register_callbacks()
function performs a registration and callback for the degrade event:

static int
event_register(void)
{
ldi_handle_t lh;
ldi_ev_callback_t callb;
ldi_ev_cookie_t dgrd_cookie;

if (ldi_ev_get_cookie(lh, LDI_EV_DEGRADE, &dgrd_cookie)
== LDI_EV_FAILURE)
goto fail;

/* no notify callbacks allowed for degrade events */
callb.cb_vers = LDI_EV_CB_VERS;
callb.cb_notify = NULL; /* NULL, notify cannot be used for
DEGRADE */
callb.cb_finalize = dgrd_finalize;

if (ldi_ev_register_callbacks(lh, dgrd_cookie, &callb, arg, &id)
!= LDI_EV_SUCCESS)
goto fail;
}

static void
event_unregister(ldi_callback_id_t id)
{
ldi_ev_remove_callbacks(id);
}

/*
* For degrade events. ldi_result will always be LDI_EV_SUCCESS
*/
static void
dgrd_finalize(ldi_handle_t lh, ldi_ev_cookie_t off_cookie,
int ldi_result, void *arg, void *ev_data)
{
ASSERT(ldi_result == LDI_EV_SUCCESS);
ASSERT(strcmp(ldi_ev_get_type(off_cookie), LDI_EV_DEGRADE) == 0);

widget_map(lh, &minor, &spec_type);

widget_reconfigure(lh, RELEASE);

ldi_ev_finalize(dip, minor, spec_type, LDI_EV_SUCCESS, d
grd_cookie, ev_data);
}