illumos: 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 it's LDI handle in it's 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
it's private "arg" parameter so that it can reopen the device
(if desired) in it's 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, it's 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
it's 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 it's 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 it's
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 it's 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 it's 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);
}