[libside.git] / src / tgif.c

// SPDX-License-Identifier: MIT
/*
 * Copyright 2022 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 */

#include <tgif/trace.h>
#include <string.h>

#include "rcu.h"
#include "list.h"

/* Top 8 bits reserved for kernel tracer use. */
#if TGIF_BITS_PER_LONG == 64
# define TGIF_EVENT_ENABLED_KERNEL_MASK			0xFF00000000000000ULL
# define TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK 	0x8000000000000000ULL

/* Allow 2^56 tracer references on an event. */
# define TGIF_EVENT_ENABLED_USER_MASK			0x00FFFFFFFFFFFFFFULL
#else
# define TGIF_EVENT_ENABLED_KERNEL_MASK			0xFF000000UL
# define TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK	0x80000000UL

/* Allow 2^24 tracer references on an event. */
# define TGIF_EVENT_ENABLED_USER_MASK			0x00FFFFFFUL
#endif

struct tgif_events_register_handle {
	struct tgif_list_node node;
	struct tgif_event_description **events;
	uint32_t nr_events;
};

struct tgif_tracer_handle {
	struct tgif_list_node node;
	void (*cb)(enum tgif_tracer_notification notif,
		struct tgif_event_description **events, uint32_t nr_events, void *priv);
	void *priv;
};

static struct tgif_rcu_gp_state rcu_gp;

/*
 * Lazy initialization for early use within library constructors.
 */
static bool initialized;
/*
 * Do not register/unregister any more events after destructor.
 */
static bool finalized;

/*
 * Recursive mutex to allow tracer callbacks to use the tgif API.
 */
static pthread_mutex_t tgif_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;

static DEFINE_TGIF_LIST_HEAD(tgif_events_list);
static DEFINE_TGIF_LIST_HEAD(tgif_tracer_list);

/*
 * The empty callback has a NULL function callback pointer, which stops
 * iteration on the array of callbacks immediately.
 */
const struct tgif_callback tgif_empty_callback = { };

void tgif_call(const struct tgif_event_description *desc, const struct tgif_arg_vec *tgif_arg_vec)
{
	struct tgif_rcu_read_state rcu_read_state;
	const struct tgif_callback *tgif_cb;
	uintptr_t enabled;

	if (tgif_unlikely(finalized))
		return;
	if (tgif_unlikely(!initialized))
		tgif_init();
	if (tgif_unlikely(desc->flags & TGIF_EVENT_FLAG_VARIADIC)) {
		printf("ERROR: unexpected variadic event description\n");
		abort();
	}
	enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
	if (tgif_unlikely(enabled & TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
		// TODO: call kernel write.
	}
	tgif_rcu_read_begin(&rcu_gp, &rcu_read_state);
	for (tgif_cb = tgif_rcu_dereference(desc->callbacks); tgif_cb->u.call != NULL; tgif_cb++)
		tgif_cb->u.call(desc, tgif_arg_vec, tgif_cb->priv);
	tgif_rcu_read_end(&rcu_gp, &rcu_read_state);
}

void tgif_call_variadic(const struct tgif_event_description *desc,
	const struct tgif_arg_vec *tgif_arg_vec,
	const struct tgif_arg_dynamic_struct *var_struct)
{
	struct tgif_rcu_read_state rcu_read_state;
	const struct tgif_callback *tgif_cb;
	uintptr_t enabled;

	if (tgif_unlikely(finalized))
		return;
	if (tgif_unlikely(!initialized))
		tgif_init();
	if (tgif_unlikely(!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))) {
		printf("ERROR: unexpected non-variadic event description\n");
		abort();
	}
	enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
	if (tgif_unlikely(enabled & TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
		// TODO: call kernel write.
	}
	tgif_rcu_read_begin(&rcu_gp, &rcu_read_state);
	for (tgif_cb = tgif_rcu_dereference(desc->callbacks); tgif_cb->u.call_variadic != NULL; tgif_cb++)
		tgif_cb->u.call_variadic(desc, tgif_arg_vec, var_struct, tgif_cb->priv);
	tgif_rcu_read_end(&rcu_gp, &rcu_read_state);
}

static
const struct tgif_callback *tgif_tracer_callback_lookup(
		const struct tgif_event_description *desc,
		void *call, void *priv)
{
	const struct tgif_callback *cb;

	for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
		if ((void *) cb->u.call == call && cb->priv == priv)
			return cb;
	}
	return NULL;
}

static
int _tgif_tracer_callback_register(struct tgif_event_description *desc,
		void *call, void *priv)
{
	struct tgif_callback *old_cb, *new_cb;
	int ret = TGIF_ERROR_OK;
	uint32_t old_nr_cb;

	if (!call)
		return TGIF_ERROR_INVAL;
	if (finalized)
		return TGIF_ERROR_EXITING;
	if (!initialized)
		tgif_init();
	pthread_mutex_lock(&tgif_lock);
	old_nr_cb = desc->nr_callbacks;
	if (old_nr_cb == UINT32_MAX) {
		ret = TGIF_ERROR_INVAL;
		goto unlock;
	}
	/* Reject duplicate (call, priv) tuples. */
	if (tgif_tracer_callback_lookup(desc, call, priv)) {
		ret = TGIF_ERROR_EXIST;
		goto unlock;
	}
	old_cb = (struct tgif_callback *) desc->callbacks;
	/* old_nr_cb + 1 (new cb) + 1 (NULL) */
	new_cb = (struct tgif_callback *) calloc(old_nr_cb + 2, sizeof(struct tgif_callback));
	if (!new_cb) {
		ret = TGIF_ERROR_NOMEM;
		goto unlock;
	}
	memcpy(new_cb, old_cb, old_nr_cb);
	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
		new_cb[old_nr_cb].u.call_variadic =
			(tgif_tracer_callback_variadic_func) call;
	else
		new_cb[old_nr_cb].u.call =
			(tgif_tracer_callback_func) call;
	new_cb[old_nr_cb].priv = priv;
	tgif_rcu_assign_pointer(desc->callbacks, new_cb);
	tgif_rcu_wait_grace_period(&rcu_gp);
	if (old_nr_cb)
		free(old_cb);
	desc->nr_callbacks++;
	/* Increment concurrently with kernel setting the top bits. */
	if (!old_nr_cb)
		(void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
unlock:
	pthread_mutex_unlock(&tgif_lock);
	return ret;
}

int tgif_tracer_callback_register(struct tgif_event_description *desc,
		tgif_tracer_callback_func call,
		void *priv)
{
	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
		return TGIF_ERROR_INVAL;
	return _tgif_tracer_callback_register(desc, (void *) call, priv);
}

int tgif_tracer_callback_variadic_register(struct tgif_event_description *desc,
		tgif_tracer_callback_variadic_func call_variadic,
		void *priv)
{
	if (!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))
		return TGIF_ERROR_INVAL;
	return _tgif_tracer_callback_register(desc, (void *) call_variadic, priv);
}

static int _tgif_tracer_callback_unregister(struct tgif_event_description *desc,
		void *call, void *priv)
{
	struct tgif_callback *old_cb, *new_cb;
	const struct tgif_callback *cb_pos;
	uint32_t pos_idx;
	int ret = TGIF_ERROR_OK;
	uint32_t old_nr_cb;

	if (!call)
		return TGIF_ERROR_INVAL;
	if (finalized)
		return TGIF_ERROR_EXITING;
	if (!initialized)
		tgif_init();
	pthread_mutex_lock(&tgif_lock);
	cb_pos = tgif_tracer_callback_lookup(desc, call, priv);
	if (!cb_pos) {
		ret = TGIF_ERROR_NOENT;
		goto unlock;
	}
	old_nr_cb = desc->nr_callbacks;
	old_cb = (struct tgif_callback *) desc->callbacks;
	if (old_nr_cb == 1) {
		new_cb = (struct tgif_callback *) &tgif_empty_callback;
	} else {
		pos_idx = cb_pos - desc->callbacks;
		/* Remove entry at pos_idx. */
		/* old_nr_cb - 1 (removed cb) + 1 (NULL) */
		new_cb = (struct tgif_callback *) calloc(old_nr_cb, sizeof(struct tgif_callback));
		if (!new_cb) {
			ret = TGIF_ERROR_NOMEM;
			goto unlock;
		}
		memcpy(new_cb, old_cb, pos_idx);
		memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
	}
	tgif_rcu_assign_pointer(desc->callbacks, new_cb);
	tgif_rcu_wait_grace_period(&rcu_gp);
	free(old_cb);
	desc->nr_callbacks--;
	/* Decrement concurrently with kernel setting the top bits. */
	if (old_nr_cb == 1)
		(void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
unlock:
	pthread_mutex_unlock(&tgif_lock);
	return ret;
}

int tgif_tracer_callback_unregister(struct tgif_event_description *desc,
		tgif_tracer_callback_func call,
		void *priv)
{
	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
		return TGIF_ERROR_INVAL;
	return _tgif_tracer_callback_unregister(desc, (void *) call, priv);
}

int tgif_tracer_callback_variadic_unregister(struct tgif_event_description *desc,
		tgif_tracer_callback_variadic_func call_variadic,
		void *priv)
{
	if (!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))
		return TGIF_ERROR_INVAL;
	return _tgif_tracer_callback_unregister(desc, (void *) call_variadic, priv);
}

struct tgif_events_register_handle *tgif_events_register(struct tgif_event_description **events, uint32_t nr_events)
{
	struct tgif_events_register_handle *events_handle = NULL;
	struct tgif_tracer_handle *tracer_handle;

	if (finalized)
		return NULL;
	if (!initialized)
		tgif_init();
	events_handle = (struct tgif_events_register_handle *)
			calloc(1, sizeof(struct tgif_events_register_handle));
	if (!events_handle)
		return NULL;
	events_handle->events = events;
	events_handle->nr_events = nr_events;

	pthread_mutex_lock(&tgif_lock);
	tgif_list_insert_node_tail(&tgif_events_list, &events_handle->node);
	tgif_list_for_each_entry(tracer_handle, &tgif_tracer_list, node) {
		tracer_handle->cb(TGIF_TRACER_NOTIFICATION_INSERT_EVENTS,
			events, nr_events, tracer_handle->priv);
	}
	pthread_mutex_unlock(&tgif_lock);
	//TODO: call event batch register ioctl
	return events_handle;
}

static
void tgif_event_remove_callbacks(struct tgif_event_description *desc)
{
	uint32_t nr_cb = desc->nr_callbacks;
	struct tgif_callback *old_cb;

	if (!nr_cb)
		return;
	old_cb = (struct tgif_callback *) desc->callbacks;
	(void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
	/*
	 * Setting the state back to 0 cb and empty callbacks out of
	 * caution. This should not matter because instrumentation is
	 * unreachable.
	 */
	desc->nr_callbacks = 0;
	tgif_rcu_assign_pointer(desc->callbacks, &tgif_empty_callback);
	/*
	 * No need to wait for grace period because instrumentation is
	 * unreachable.
	 */
	free(old_cb);
}

/*
 * Unregister event handle. At this point, all tgif events in that
 * handle should be unreachable.
 */
void tgif_events_unregister(struct tgif_events_register_handle *events_handle)
{
	struct tgif_tracer_handle *tracer_handle;
	uint32_t i;

	if (!events_handle)
		return;
	if (finalized)
		return;
	if (!initialized)
		tgif_init();
	pthread_mutex_lock(&tgif_lock);
	tgif_list_remove_node(&events_handle->node);
	tgif_list_for_each_entry(tracer_handle, &tgif_tracer_list, node) {
		tracer_handle->cb(TGIF_TRACER_NOTIFICATION_REMOVE_EVENTS,
			events_handle->events, events_handle->nr_events,
			tracer_handle->priv);
	}
	for (i = 0; i < events_handle->nr_events; i++) {
		struct tgif_event_description *event = events_handle->events[i];

		/* Skip NULL pointers */
		if (!event)
			continue;
		tgif_event_remove_callbacks(event);
	}
	pthread_mutex_unlock(&tgif_lock);
	//TODO: call event batch unregister ioctl
	free(events_handle);
}

struct tgif_tracer_handle *tgif_tracer_event_notification_register(
		void (*cb)(enum tgif_tracer_notification notif,
			struct tgif_event_description **events, uint32_t nr_events, void *priv),
		void *priv)
{
	struct tgif_tracer_handle *tracer_handle;
	struct tgif_events_register_handle *events_handle;

	if (finalized)
		return NULL;
	if (!initialized)
		tgif_init();
	tracer_handle = (struct tgif_tracer_handle *)
				calloc(1, sizeof(struct tgif_tracer_handle));
	if (!tracer_handle)
		return NULL;
	pthread_mutex_lock(&tgif_lock);
	tracer_handle->cb = cb;
	tracer_handle->priv = priv;
	tgif_list_insert_node_tail(&tgif_tracer_list, &tracer_handle->node);
	tgif_list_for_each_entry(events_handle, &tgif_events_list, node) {
		cb(TGIF_TRACER_NOTIFICATION_INSERT_EVENTS,
			events_handle->events, events_handle->nr_events, priv);
	}
	pthread_mutex_unlock(&tgif_lock);
	return tracer_handle;
}

void tgif_tracer_event_notification_unregister(struct tgif_tracer_handle *tracer_handle)
{
	struct tgif_events_register_handle *events_handle;

	if (finalized)
		return;
	if (!initialized)
		tgif_init();
	pthread_mutex_lock(&tgif_lock);
	tgif_list_for_each_entry(events_handle, &tgif_events_list, node) {
		tracer_handle->cb(TGIF_TRACER_NOTIFICATION_REMOVE_EVENTS,
			events_handle->events, events_handle->nr_events,
			tracer_handle->priv);
	}
	tgif_list_remove_node(&tracer_handle->node);
	pthread_mutex_unlock(&tgif_lock);
}

void tgif_init(void)
{
	if (initialized)
		return;
	tgif_rcu_gp_init(&rcu_gp);
	initialized = true;
}

/*
 * tgif_exit() is executed from a library destructor. It can be called
 * explicitly at application exit as well. Concurrent tgif API use is
 * not expected at that point.
 */
void tgif_exit(void)
{
	struct tgif_events_register_handle *handle, *tmp;

	if (finalized)
		return;
	tgif_list_for_each_entry_safe(handle, tmp, &tgif_events_list, node)
		tgif_events_unregister(handle);
	tgif_rcu_gp_exit(&rcu_gp);
	finalized = true;
}
Commit	Line	Data
d04d4903 MD	1	// SPDX-License-Identifier: MIT
	2	/*
	3	* Copyright 2022 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	4	*/
	5
	6	#include <tgif/trace.h>
	7	#include <string.h>
	8
	9	#include "rcu.h"
	10	#include "list.h"
	11
	12	/* Top 8 bits reserved for kernel tracer use. */
	13	#if TGIF_BITS_PER_LONG == 64
	14	# define TGIF_EVENT_ENABLED_KERNEL_MASK 0xFF00000000000000ULL
	15	# define TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK 0x8000000000000000ULL
	16
	17	/* Allow 2^56 tracer references on an event. */
	18	# define TGIF_EVENT_ENABLED_USER_MASK 0x00FFFFFFFFFFFFFFULL
	19	#else
	20	# define TGIF_EVENT_ENABLED_KERNEL_MASK 0xFF000000UL
	21	# define TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK 0x80000000UL
	22
	23	/* Allow 2^24 tracer references on an event. */
	24	# define TGIF_EVENT_ENABLED_USER_MASK 0x00FFFFFFUL
	25	#endif
	26
	27	struct tgif_events_register_handle {
	28	struct tgif_list_node node;
	29	struct tgif_event_description **events;
	30	uint32_t nr_events;
	31	};
	32
	33	struct tgif_tracer_handle {
	34	struct tgif_list_node node;
	35	void (*cb)(enum tgif_tracer_notification notif,
	36	struct tgif_event_description *events, uint32_t nr_events, void priv);
	37	void *priv;
	38	};
	39
	40	static struct tgif_rcu_gp_state rcu_gp;
	41
	42	/*
	43	* Lazy initialization for early use within library constructors.
	44	*/
	45	static bool initialized;
	46	/*
	47	* Do not register/unregister any more events after destructor.
	48	*/
	49	static bool finalized;
	50
	51	/*
	52	* Recursive mutex to allow tracer callbacks to use the tgif API.
	53	*/
	54	static pthread_mutex_t tgif_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
	55
	56	static DEFINE_TGIF_LIST_HEAD(tgif_events_list);
	57	static DEFINE_TGIF_LIST_HEAD(tgif_tracer_list);
	58
	59	/*
	60	* The empty callback has a NULL function callback pointer, which stops
	61	* iteration on the array of callbacks immediately.
	62	*/
	63	const struct tgif_callback tgif_empty_callback = { };
	64
65	void tgif_call(const struct tgif_event_description desc, const struct tgif_arg_vec tgif_arg_vec)
66	{
67	struct tgif_rcu_read_state rcu_read_state;
68	const struct tgif_callback *tgif_cb;
69	uintptr_t enabled;
70
71	if (tgif_unlikely(finalized))
72	return;
73	if (tgif_unlikely(!initialized))
74	tgif_init();
75	if (tgif_unlikely(desc->flags & TGIF_EVENT_FLAG_VARIADIC)) {
76	printf("ERROR: unexpected variadic event description\n");
77	abort();
78	}
79	enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
80	if (tgif_unlikely(enabled & TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
81	// TODO: call kernel write.
82	}
83	tgif_rcu_read_begin(&rcu_gp, &rcu_read_state);
84	for (tgif_cb = tgif_rcu_dereference(desc->callbacks); tgif_cb->u.call != NULL; tgif_cb++)
85	tgif_cb->u.call(desc, tgif_arg_vec, tgif_cb->priv);
86	tgif_rcu_read_end(&rcu_gp, &rcu_read_state);
87	}
88
89	void tgif_call_variadic(const struct tgif_event_description *desc,
90	const struct tgif_arg_vec *tgif_arg_vec,
91	const struct tgif_arg_dynamic_struct *var_struct)
92	{
93	struct tgif_rcu_read_state rcu_read_state;
94	const struct tgif_callback *tgif_cb;
95	uintptr_t enabled;
96
97	if (tgif_unlikely(finalized))
98	return;
99	if (tgif_unlikely(!initialized))
100	tgif_init();
101	if (tgif_unlikely(!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))) {
102	printf("ERROR: unexpected non-variadic event description\n");
103	abort();
104	}
105	enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
106	if (tgif_unlikely(enabled & TGIF_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
107	// TODO: call kernel write.
108	}
109	tgif_rcu_read_begin(&rcu_gp, &rcu_read_state);
110	for (tgif_cb = tgif_rcu_dereference(desc->callbacks); tgif_cb->u.call_variadic != NULL; tgif_cb++)
111	tgif_cb->u.call_variadic(desc, tgif_arg_vec, var_struct, tgif_cb->priv);
112	tgif_rcu_read_end(&rcu_gp, &rcu_read_state);
113	}
114
115	static
116	const struct tgif_callback *tgif_tracer_callback_lookup(
117	const struct tgif_event_description *desc,
118	void call, void priv)
119	{
120	const struct tgif_callback *cb;
121
122	for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
123	if ((void *) cb->u.call == call && cb->priv == priv)
124	return cb;
125	}
126	return NULL;
127	}
128
129	static
130	int _tgif_tracer_callback_register(struct tgif_event_description *desc,
131	void call, void priv)
132	{
133	struct tgif_callback old_cb, new_cb;
134	int ret = TGIF_ERROR_OK;
135	uint32_t old_nr_cb;
136
137	if (!call)
138	return TGIF_ERROR_INVAL;
139	if (finalized)
140	return TGIF_ERROR_EXITING;
141	if (!initialized)
142	tgif_init();
143	pthread_mutex_lock(&tgif_lock);
144	old_nr_cb = desc->nr_callbacks;
145	if (old_nr_cb == UINT32_MAX) {
146	ret = TGIF_ERROR_INVAL;
147	goto unlock;
148	}
149	/* Reject duplicate (call, priv) tuples. */
150	if (tgif_tracer_callback_lookup(desc, call, priv)) {
151	ret = TGIF_ERROR_EXIST;
152	goto unlock;
153	}
154	old_cb = (struct tgif_callback *) desc->callbacks;
155	/* old_nr_cb + 1 (new cb) + 1 (NULL) */
156	new_cb = (struct tgif_callback *) calloc(old_nr_cb + 2, sizeof(struct tgif_callback));
157	if (!new_cb) {
158	ret = TGIF_ERROR_NOMEM;
159	goto unlock;
160	}
161	memcpy(new_cb, old_cb, old_nr_cb);
162	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
163	new_cb[old_nr_cb].u.call_variadic =
164	(tgif_tracer_callback_variadic_func) call;
165	else
166	new_cb[old_nr_cb].u.call =
167	(tgif_tracer_callback_func) call;
168	new_cb[old_nr_cb].priv = priv;
169	tgif_rcu_assign_pointer(desc->callbacks, new_cb);
170	tgif_rcu_wait_grace_period(&rcu_gp);
171	if (old_nr_cb)
172	free(old_cb);
173	desc->nr_callbacks++;
174	/* Increment concurrently with kernel setting the top bits. */
175	if (!old_nr_cb)
176	(void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
177	unlock:
178	pthread_mutex_unlock(&tgif_lock);
179	return ret;
180	}
181
182	int tgif_tracer_callback_register(struct tgif_event_description *desc,
183	tgif_tracer_callback_func call,
184	void *priv)
185	{
186	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
187	return TGIF_ERROR_INVAL;
188	return _tgif_tracer_callback_register(desc, (void *) call, priv);
189	}
190
191	int tgif_tracer_callback_variadic_register(struct tgif_event_description *desc,
192	tgif_tracer_callback_variadic_func call_variadic,
193	void *priv)
194	{
195	if (!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))
196	return TGIF_ERROR_INVAL;
197	return _tgif_tracer_callback_register(desc, (void *) call_variadic, priv);
198	}
199
200	static int _tgif_tracer_callback_unregister(struct tgif_event_description *desc,
201	void call, void priv)
202	{
203	struct tgif_callback old_cb, new_cb;
204	const struct tgif_callback *cb_pos;
205	uint32_t pos_idx;
206	int ret = TGIF_ERROR_OK;
207	uint32_t old_nr_cb;
208
209	if (!call)
210	return TGIF_ERROR_INVAL;
211	if (finalized)
212	return TGIF_ERROR_EXITING;
213	if (!initialized)
214	tgif_init();
215	pthread_mutex_lock(&tgif_lock);
216	cb_pos = tgif_tracer_callback_lookup(desc, call, priv);
217	if (!cb_pos) {
218	ret = TGIF_ERROR_NOENT;
219	goto unlock;
220	}
221	old_nr_cb = desc->nr_callbacks;
222	old_cb = (struct tgif_callback *) desc->callbacks;
223	if (old_nr_cb == 1) {
224	new_cb = (struct tgif_callback *) &tgif_empty_callback;
225	} else {
226	pos_idx = cb_pos - desc->callbacks;
227	/* Remove entry at pos_idx. */
228	/* old_nr_cb - 1 (removed cb) + 1 (NULL) */
229	new_cb = (struct tgif_callback *) calloc(old_nr_cb, sizeof(struct tgif_callback));
230	if (!new_cb) {
231	ret = TGIF_ERROR_NOMEM;
232	goto unlock;
233	}
234	memcpy(new_cb, old_cb, pos_idx);
235	memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
236	}
237	tgif_rcu_assign_pointer(desc->callbacks, new_cb);
238	tgif_rcu_wait_grace_period(&rcu_gp);
239	free(old_cb);
240	desc->nr_callbacks--;
241	/* Decrement concurrently with kernel setting the top bits. */
242	if (old_nr_cb == 1)
243	(void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
244	unlock:
245	pthread_mutex_unlock(&tgif_lock);
246	return ret;
247	}
248
249	int tgif_tracer_callback_unregister(struct tgif_event_description *desc,
250	tgif_tracer_callback_func call,
251	void *priv)
252	{
253	if (desc->flags & TGIF_EVENT_FLAG_VARIADIC)
254	return TGIF_ERROR_INVAL;
255	return _tgif_tracer_callback_unregister(desc, (void *) call, priv);
256	}
257
258	int tgif_tracer_callback_variadic_unregister(struct tgif_event_description *desc,
259	tgif_tracer_callback_variadic_func call_variadic,
260	void *priv)
261	{
262	if (!(desc->flags & TGIF_EVENT_FLAG_VARIADIC))
263	return TGIF_ERROR_INVAL;
264	return _tgif_tracer_callback_unregister(desc, (void *) call_variadic, priv);
265	}
266
267	struct tgif_events_register_handle tgif_events_register(struct tgif_event_description *events, uint32_t nr_events)
268	{
269	struct tgif_events_register_handle *events_handle = NULL;
270	struct tgif_tracer_handle *tracer_handle;
271
272	if (finalized)
273	return NULL;
274	if (!initialized)
275	tgif_init();
276	events_handle = (struct tgif_events_register_handle *)
277	calloc(1, sizeof(struct tgif_events_register_handle));
278	if (!events_handle)
279	return NULL;
280	events_handle->events = events;
281	events_handle->nr_events = nr_events;
282
283	pthread_mutex_lock(&tgif_lock);
284	tgif_list_insert_node_tail(&tgif_events_list, &events_handle->node);
285	tgif_list_for_each_entry(tracer_handle, &tgif_tracer_list, node) {
286	tracer_handle->cb(TGIF_TRACER_NOTIFICATION_INSERT_EVENTS,
287	events, nr_events, tracer_handle->priv);
288	}
289	pthread_mutex_unlock(&tgif_lock);
290	//TODO: call event batch register ioctl
291	return events_handle;
292	}
293
294	static
295	void tgif_event_remove_callbacks(struct tgif_event_description *desc)
296	{
297	uint32_t nr_cb = desc->nr_callbacks;
298	struct tgif_callback *old_cb;
299
300	if (!nr_cb)
301	return;
302	old_cb = (struct tgif_callback *) desc->callbacks;
303	(void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
304	/*
305	* Setting the state back to 0 cb and empty callbacks out of
306	* caution. This should not matter because instrumentation is
307	* unreachable.
308	*/
309	desc->nr_callbacks = 0;
310	tgif_rcu_assign_pointer(desc->callbacks, &tgif_empty_callback);
311	/*
312	* No need to wait for grace period because instrumentation is
313	* unreachable.
314	*/
315	free(old_cb);
316	}
317
318	/*
319	* Unregister event handle. At this point, all tgif events in that
320	* handle should be unreachable.
321	*/
322	void tgif_events_unregister(struct tgif_events_register_handle *events_handle)
323	{
324	struct tgif_tracer_handle *tracer_handle;
325	uint32_t i;
326
327	if (!events_handle)
328	return;
329	if (finalized)
330	return;
331	if (!initialized)
332	tgif_init();
333	pthread_mutex_lock(&tgif_lock);
334	tgif_list_remove_node(&events_handle->node);
335	tgif_list_for_each_entry(tracer_handle, &tgif_tracer_list, node) {
336	tracer_handle->cb(TGIF_TRACER_NOTIFICATION_REMOVE_EVENTS,
337	events_handle->events, events_handle->nr_events,
338	tracer_handle->priv);
339	}
340	for (i = 0; i < events_handle->nr_events; i++) {
341	struct tgif_event_description *event = events_handle->events[i];
342
343	/* Skip NULL pointers */
344	if (!event)
345	continue;
346	tgif_event_remove_callbacks(event);
347	}
348	pthread_mutex_unlock(&tgif_lock);
349	//TODO: call event batch unregister ioctl
350	free(events_handle);
351	}
352
353	struct tgif_tracer_handle *tgif_tracer_event_notification_register(
354	void (*cb)(enum tgif_tracer_notification notif,
355	struct tgif_event_description *events, uint32_t nr_events, void priv),
356	void *priv)
357	{
358	struct tgif_tracer_handle *tracer_handle;
359	struct tgif_events_register_handle *events_handle;
360
361	if (finalized)
362	return NULL;
363	if (!initialized)
364	tgif_init();
365	tracer_handle = (struct tgif_tracer_handle *)
366	calloc(1, sizeof(struct tgif_tracer_handle));
367	if (!tracer_handle)
368	return NULL;
369	pthread_mutex_lock(&tgif_lock);
370	tracer_handle->cb = cb;
371	tracer_handle->priv = priv;
372	tgif_list_insert_node_tail(&tgif_tracer_list, &tracer_handle->node);
373	tgif_list_for_each_entry(events_handle, &tgif_events_list, node) {
374	cb(TGIF_TRACER_NOTIFICATION_INSERT_EVENTS,
375	events_handle->events, events_handle->nr_events, priv);
376	}
377	pthread_mutex_unlock(&tgif_lock);
378	return tracer_handle;
379	}
380
381	void tgif_tracer_event_notification_unregister(struct tgif_tracer_handle *tracer_handle)
382	{
383	struct tgif_events_register_handle *events_handle;
384
385	if (finalized)
386	return;
387	if (!initialized)
388	tgif_init();
389	pthread_mutex_lock(&tgif_lock);
390	tgif_list_for_each_entry(events_handle, &tgif_events_list, node) {
391	tracer_handle->cb(TGIF_TRACER_NOTIFICATION_REMOVE_EVENTS,
392	events_handle->events, events_handle->nr_events,
393	tracer_handle->priv);
394	}
395	tgif_list_remove_node(&tracer_handle->node);
396	pthread_mutex_unlock(&tgif_lock);
397	}
398
399	void tgif_init(void)
400	{
401	if (initialized)
402	return;
403	tgif_rcu_gp_init(&rcu_gp);
404	initialized = true;
405	}
406
407	/*
408	* tgif_exit() is executed from a library destructor. It can be called
409	* explicitly at application exit as well. Concurrent tgif API use is
410	* not expected at that point.
411	*/
412	void tgif_exit(void)
413	{
414	struct tgif_events_register_handle handle, tmp;
415
416	if (finalized)
417	return;
418	tgif_list_for_each_entry_safe(handle, tmp, &tgif_events_list, node)
419	tgif_events_unregister(handle);
420	tgif_rcu_gp_exit(&rcu_gp);
421	finalized = true;
422	}