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man pages section 9: DDI and DKI Kernel Functions

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Updated: Thursday, June 13, 2019
 
 

ldi_ev_register_callbacks(9F)

Name

ldi_ev_register_callbacks - add a notify and/or finalize callback

Synopsis

#include <sys/sunldi.h>

int ldi_ev_get_cookie(ldi_handle_t lh, ldi_ev_cookie_t *cookie, 
      ldi_ev_callback_t *callb, void *arg, ldi_ev_callback_id_t *id);

Interface Level

Solaris DDI specific (Solaris 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_ev_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_ev_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_ev_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_ev_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);
}


See Also

ldi_ev_finalize(9F), ldi_ev_get_cookie(9F), ldi_ev_notify(9F), ldi_ev_remove_callbacks(9F)