[deliverable/linux.git] / drivers / mtd / ubi / fastmap-wl.c

/*
 * Copyright (c) 2012 Linutronix GmbH
 * Copyright (c) 2014 sigma star gmbh
 * Author: Richard Weinberger <richard@nod.at>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
 * the GNU General Public License for more details.
 *
 */

/**
 * update_fastmap_work_fn - calls ubi_update_fastmap from a work queue
 * @wrk: the work description object
 */
static void update_fastmap_work_fn(struct work_struct *wrk)
{
	struct ubi_device *ubi = container_of(wrk, struct ubi_device, fm_work);
	ubi_update_fastmap(ubi);
	spin_lock(&ubi->wl_lock);
	ubi->fm_work_scheduled = 0;
	spin_unlock(&ubi->wl_lock);
}

/**
 *  is_fm_block - returns 1 if a PEB is currently used in a fastmap.
 *  @ubi: UBI device description object
 *  @pnum: the to be checked PEB
 */
static int is_fm_block(struct ubi_device *ubi, int pnum)
{
	int i;

	if (!ubi->fm)
		return 0;

	for (i = 0; i < ubi->fm->used_blocks; i++)
		if (ubi->fm->e[i]->pnum == pnum)
			return 1;

	return 0;
}

/**
 * find_anchor_wl_entry - find wear-leveling entry to used as anchor PEB.
 * @root: the RB-tree where to look for
 */
static struct ubi_wl_entry *find_anchor_wl_entry(struct rb_root *root)
{
	struct rb_node *p;
	struct ubi_wl_entry *e, *victim = NULL;
	int max_ec = UBI_MAX_ERASECOUNTER;

	ubi_rb_for_each_entry(p, e, root, u.rb) {
		if (e->pnum < UBI_FM_MAX_START && e->ec < max_ec) {
			victim = e;
			max_ec = e->ec;
		}
	}

	return victim;
}

/**
 * return_unused_pool_pebs - returns unused PEB to the free tree.
 * @ubi: UBI device description object
 * @pool: fastmap pool description object
 */
static void return_unused_pool_pebs(struct ubi_device *ubi,
				    struct ubi_fm_pool *pool)
{
	int i;
	struct ubi_wl_entry *e;

	for (i = pool->used; i < pool->size; i++) {
		e = ubi->lookuptbl[pool->pebs[i]];
		wl_tree_add(e, &ubi->free);
		ubi->free_count++;
	}
}

static int anchor_pebs_avalible(struct rb_root *root)
{
	struct rb_node *p;
	struct ubi_wl_entry *e;

	ubi_rb_for_each_entry(p, e, root, u.rb)
		if (e->pnum < UBI_FM_MAX_START)
			return 1;

	return 0;
}

/**
 * ubi_wl_get_fm_peb - find a physical erase block with a given maximal number.
 * @ubi: UBI device description object
 * @anchor: This PEB will be used as anchor PEB by fastmap
 *
 * The function returns a physical erase block with a given maximal number
 * and removes it from the wl subsystem.
 * Must be called with wl_lock held!
 */
struct ubi_wl_entry *ubi_wl_get_fm_peb(struct ubi_device *ubi, int anchor)
{
	struct ubi_wl_entry *e = NULL;

	if (!ubi->free.rb_node || (ubi->free_count - ubi->beb_rsvd_pebs < 1))
		goto out;

	if (anchor)
		e = find_anchor_wl_entry(&ubi->free);
	else
		e = find_mean_wl_entry(ubi, &ubi->free);

	if (!e)
		goto out;

	self_check_in_wl_tree(ubi, e, &ubi->free);

	/* remove it from the free list,
	 * the wl subsystem does no longer know this erase block */
	rb_erase(&e->u.rb, &ubi->free);
	ubi->free_count--;
out:
	return e;
}

/**
 * ubi_refill_pools - refills all fastmap PEB pools.
 * @ubi: UBI device description object
 */
void ubi_refill_pools(struct ubi_device *ubi)
{
	struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;
	struct ubi_fm_pool *pool = &ubi->fm_pool;
	struct ubi_wl_entry *e;
	int enough;

	spin_lock(&ubi->wl_lock);

	return_unused_pool_pebs(ubi, wl_pool);
	return_unused_pool_pebs(ubi, pool);

	wl_pool->size = 0;
	pool->size = 0;

	for (;;) {
		enough = 0;
		if (pool->size < pool->max_size) {
			if (!ubi->free.rb_node)
				break;

			e = wl_get_wle(ubi);
			if (!e)
				break;

			pool->pebs[pool->size] = e->pnum;
			pool->size++;
		} else
			enough++;

		if (wl_pool->size < wl_pool->max_size) {
			if (!ubi->free.rb_node ||
			   (ubi->free_count - ubi->beb_rsvd_pebs < 5))
				break;

			e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
			self_check_in_wl_tree(ubi, e, &ubi->free);
			rb_erase(&e->u.rb, &ubi->free);
			ubi->free_count--;

			wl_pool->pebs[wl_pool->size] = e->pnum;
			wl_pool->size++;
		} else
			enough++;

		if (enough == 2)
			break;
	}

	wl_pool->used = 0;
	pool->used = 0;

	spin_unlock(&ubi->wl_lock);
}

/**
 * ubi_wl_get_peb - get a physical eraseblock.
 * @ubi: UBI device description object
 *
 * This function returns a physical eraseblock in case of success and a
 * negative error code in case of failure.
 * Returns with ubi->fm_eba_sem held in read mode!
 */
int ubi_wl_get_peb(struct ubi_device *ubi)
{
	int ret, retried = 0;
	struct ubi_fm_pool *pool = &ubi->fm_pool;
	struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;

again:
	down_read(&ubi->fm_eba_sem);
	spin_lock(&ubi->wl_lock);

	/* We check here also for the WL pool because at this point we can
	 * refill the WL pool synchronous. */
	if (pool->used == pool->size || wl_pool->used == wl_pool->size) {
		spin_unlock(&ubi->wl_lock);
		up_read(&ubi->fm_eba_sem);
		ret = ubi_update_fastmap(ubi);
		if (ret) {
			ubi_msg(ubi, "Unable to write a new fastmap: %i", ret);
			down_read(&ubi->fm_eba_sem);
			return -ENOSPC;
		}
		down_read(&ubi->fm_eba_sem);
		spin_lock(&ubi->wl_lock);
	}

	if (pool->used == pool->size) {
		spin_unlock(&ubi->wl_lock);
		if (retried) {
			ubi_err(ubi, "Unable to get a free PEB from user WL pool");
			ret = -ENOSPC;
			goto out;
		}
		retried = 1;
		up_read(&ubi->fm_eba_sem);
		goto again;
	}

	ubi_assert(pool->used < pool->size);
	ret = pool->pebs[pool->used++];
	prot_queue_add(ubi, ubi->lookuptbl[ret]);
	spin_unlock(&ubi->wl_lock);
out:
	return ret;
}

/* get_peb_for_wl - returns a PEB to be used internally by the WL sub-system.
 *
 * @ubi: UBI device description object
 */
static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
{
	struct ubi_fm_pool *pool = &ubi->fm_wl_pool;
	int pnum;

	if (pool->used == pool->size) {
		/* We cannot update the fastmap here because this
		 * function is called in atomic context.
		 * Let's fail here and refill/update it as soon as possible. */
		if (!ubi->fm_work_scheduled) {
			ubi->fm_work_scheduled = 1;
			schedule_work(&ubi->fm_work);
		}
		return NULL;
	}

	pnum = pool->pebs[pool->used++];
	return ubi->lookuptbl[pnum];
}

/**
 * ubi_ensure_anchor_pebs - schedule wear-leveling to produce an anchor PEB.
 * @ubi: UBI device description object
 */
int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
{
	struct ubi_work *wrk;

	spin_lock(&ubi->wl_lock);
	if (ubi->wl_scheduled) {
		spin_unlock(&ubi->wl_lock);
		return 0;
	}
	ubi->wl_scheduled = 1;
	spin_unlock(&ubi->wl_lock);

	wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
	if (!wrk) {
		spin_lock(&ubi->wl_lock);
		ubi->wl_scheduled = 0;
		spin_unlock(&ubi->wl_lock);
		return -ENOMEM;
	}

	wrk->anchor = 1;
	wrk->func = &wear_leveling_worker;
	schedule_ubi_work(ubi, wrk);
	return 0;
}

/**
 * ubi_wl_put_fm_peb - returns a PEB used in a fastmap to the wear-leveling
 * sub-system.
 * see: ubi_wl_put_peb()
 *
 * @ubi: UBI device description object
 * @fm_e: physical eraseblock to return
 * @lnum: the last used logical eraseblock number for the PEB
 * @torture: if this physical eraseblock has to be tortured
 */
int ubi_wl_put_fm_peb(struct ubi_device *ubi, struct ubi_wl_entry *fm_e,
		      int lnum, int torture)
{
	struct ubi_wl_entry *e;
	int vol_id, pnum = fm_e->pnum;

	dbg_wl("PEB %d", pnum);

	ubi_assert(pnum >= 0);
	ubi_assert(pnum < ubi->peb_count);

	spin_lock(&ubi->wl_lock);
	e = ubi->lookuptbl[pnum];

	/* This can happen if we recovered from a fastmap the very
	 * first time and writing now a new one. In this case the wl system
	 * has never seen any PEB used by the original fastmap.
	 */
	if (!e) {
		e = fm_e;
		ubi_assert(e->ec >= 0);
		ubi->lookuptbl[pnum] = e;
	}

	spin_unlock(&ubi->wl_lock);

	vol_id = lnum ? UBI_FM_DATA_VOLUME_ID : UBI_FM_SB_VOLUME_ID;
	return schedule_erase(ubi, e, vol_id, lnum, torture);
}

/**
 * ubi_is_erase_work - checks whether a work is erase work.
 * @wrk: The work object to be checked
 */
int ubi_is_erase_work(struct ubi_work *wrk)
{
	return wrk->func == erase_worker;
}

static void ubi_fastmap_close(struct ubi_device *ubi)
{
	int i;

	flush_work(&ubi->fm_work);
	return_unused_pool_pebs(ubi, &ubi->fm_pool);
	return_unused_pool_pebs(ubi, &ubi->fm_wl_pool);

	if (ubi->fm) {
		for (i = 0; i < ubi->fm->used_blocks; i++)
			kfree(ubi->fm->e[i]);
	}
	kfree(ubi->fm);
}

/**
 * may_reserve_for_fm - tests whether a PEB shall be reserved for fastmap.
 * See find_mean_wl_entry()
 *
 * @ubi: UBI device description object
 * @e: physical eraseblock to return
 * @root: RB tree to test against.
 */
static struct ubi_wl_entry *may_reserve_for_fm(struct ubi_device *ubi,
					   struct ubi_wl_entry *e,
					   struct rb_root *root) {
	if (e && !ubi->fm_disabled && !ubi->fm &&
	    e->pnum < UBI_FM_MAX_START)
		e = rb_entry(rb_next(root->rb_node),
			     struct ubi_wl_entry, u.rb);

	return e;
}
Commit	Line	Data
78d6d497 RW	1	/*
	2	* Copyright (c) 2012 Linutronix GmbH
	3	* Copyright (c) 2014 sigma star gmbh
	4	* Author: Richard Weinberger <richard@nod.at>
	5	*
	6	* This program is free software; you can redistribute it and/or modify
	7	* it under the terms of the GNU General Public License as published by
	8	* the Free Software Foundation; version 2.
	9	*
	10	* This program is distributed in the hope that it will be useful,
	11	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
	13	* the GNU General Public License for more details.
	14	*
	15	*/
	16
	17	/**
	18	* update_fastmap_work_fn - calls ubi_update_fastmap from a work queue
	19	* @wrk: the work description object
	20	*/
	21	static void update_fastmap_work_fn(struct work_struct *wrk)
	22	{
	23	struct ubi_device *ubi = container_of(wrk, struct ubi_device, fm_work);
	24	ubi_update_fastmap(ubi);
	25	spin_lock(&ubi->wl_lock);
	26	ubi->fm_work_scheduled = 0;
	27	spin_unlock(&ubi->wl_lock);
	28	}
	29
	30	/**
	31	* is_fm_block - returns 1 if a PEB is currently used in a fastmap.
	32	* @ubi: UBI device description object
	33	* @pnum: the to be checked PEB
	34	*/
	35	static int is_fm_block(struct ubi_device *ubi, int pnum)
	36	{
	37	int i;
	38
	39	if (!ubi->fm)
	40	return 0;
	41
	42	for (i = 0; i < ubi->fm->used_blocks; i++)
	43	if (ubi->fm->e[i]->pnum == pnum)
	44	return 1;
	45
	46	return 0;
	47	}
	48
	49	/**
	50	* find_anchor_wl_entry - find wear-leveling entry to used as anchor PEB.
	51	* @root: the RB-tree where to look for
	52	*/
	53	static struct ubi_wl_entry find_anchor_wl_entry(struct rb_root root)
	54	{
	55	struct rb_node *p;
	56	struct ubi_wl_entry e, victim = NULL;
	57	int max_ec = UBI_MAX_ERASECOUNTER;
	58
	59	ubi_rb_for_each_entry(p, e, root, u.rb) {
	60	if (e->pnum < UBI_FM_MAX_START && e->ec < max_ec) {
	61	victim = e;
	62	max_ec = e->ec;
	63	}
	64	}
65
66	return victim;
67	}
68
69	/**
70	* return_unused_pool_pebs - returns unused PEB to the free tree.
71	* @ubi: UBI device description object
72	* @pool: fastmap pool description object
73	*/
74	static void return_unused_pool_pebs(struct ubi_device *ubi,
75	struct ubi_fm_pool *pool)
76	{
77	int i;
78	struct ubi_wl_entry *e;
79
80	for (i = pool->used; i < pool->size; i++) {
81	e = ubi->lookuptbl[pool->pebs[i]];
82	wl_tree_add(e, &ubi->free);
83	ubi->free_count++;
84	}
85	}
86
87	static int anchor_pebs_avalible(struct rb_root *root)
88	{
89	struct rb_node *p;
90	struct ubi_wl_entry *e;
91
92	ubi_rb_for_each_entry(p, e, root, u.rb)
93	if (e->pnum < UBI_FM_MAX_START)
94	return 1;
95
96	return 0;
97	}
98
99	/**
100	* ubi_wl_get_fm_peb - find a physical erase block with a given maximal number.
101	* @ubi: UBI device description object
102	* @anchor: This PEB will be used as anchor PEB by fastmap
103	*
104	* The function returns a physical erase block with a given maximal number
105	* and removes it from the wl subsystem.
106	* Must be called with wl_lock held!
107	*/
108	struct ubi_wl_entry ubi_wl_get_fm_peb(struct ubi_device ubi, int anchor)
109	{
110	struct ubi_wl_entry *e = NULL;
111
112	if (!ubi->free.rb_node \|\| (ubi->free_count - ubi->beb_rsvd_pebs < 1))
113	goto out;
114
115	if (anchor)
116	e = find_anchor_wl_entry(&ubi->free);
117	else
118	e = find_mean_wl_entry(ubi, &ubi->free);
119
120	if (!e)
121	goto out;
122
123	self_check_in_wl_tree(ubi, e, &ubi->free);
124
125	/* remove it from the free list,
126	* the wl subsystem does no longer know this erase block */
127	rb_erase(&e->u.rb, &ubi->free);
128	ubi->free_count--;
129	out:
130	return e;
131	}
132
133	/**
134	* ubi_refill_pools - refills all fastmap PEB pools.
135	* @ubi: UBI device description object
136	*/
137	void ubi_refill_pools(struct ubi_device *ubi)
138	{
139	struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;
140	struct ubi_fm_pool *pool = &ubi->fm_pool;
141	struct ubi_wl_entry *e;
142	int enough;
143
144	spin_lock(&ubi->wl_lock);
145
146	return_unused_pool_pebs(ubi, wl_pool);
147	return_unused_pool_pebs(ubi, pool);
148
149	wl_pool->size = 0;
150	pool->size = 0;
151
152	for (;;) {
153	enough = 0;
154	if (pool->size < pool->max_size) {
155	if (!ubi->free.rb_node)
156	break;
157
158	e = wl_get_wle(ubi);
159	if (!e)
160	break;
161
162	pool->pebs[pool->size] = e->pnum;
163	pool->size++;
164	} else
165	enough++;
166
167	if (wl_pool->size < wl_pool->max_size) {
168	if (!ubi->free.rb_node \|\|
169	(ubi->free_count - ubi->beb_rsvd_pebs < 5))
170	break;
171
172	e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
173	self_check_in_wl_tree(ubi, e, &ubi->free);
174	rb_erase(&e->u.rb, &ubi->free);
175	ubi->free_count--;
176
177	wl_pool->pebs[wl_pool->size] = e->pnum;
178	wl_pool->size++;
179	} else
180	enough++;
181
182	if (enough == 2)
183	break;
184	}
185
186	wl_pool->used = 0;
187	pool->used = 0;
188
189	spin_unlock(&ubi->wl_lock);
190	}
191
192	/**
193	* ubi_wl_get_peb - get a physical eraseblock.
194	* @ubi: UBI device description object
195	*
196	* This function returns a physical eraseblock in case of success and a
197	* negative error code in case of failure.
198	* Returns with ubi->fm_eba_sem held in read mode!
199	*/
200	int ubi_wl_get_peb(struct ubi_device *ubi)
201	{
202	int ret, retried = 0;
203	struct ubi_fm_pool *pool = &ubi->fm_pool;
204	struct ubi_fm_pool *wl_pool = &ubi->fm_wl_pool;
205
206	again:
207	down_read(&ubi->fm_eba_sem);
208	spin_lock(&ubi->wl_lock);
209
210	/* We check here also for the WL pool because at this point we can
211	* refill the WL pool synchronous. */
212	if (pool->used == pool->size \|\| wl_pool->used == wl_pool->size) {
213	spin_unlock(&ubi->wl_lock);
214	up_read(&ubi->fm_eba_sem);
215	ret = ubi_update_fastmap(ubi);
216	if (ret) {
217	ubi_msg(ubi, "Unable to write a new fastmap: %i", ret);
218	down_read(&ubi->fm_eba_sem);
219	return -ENOSPC;
220	}
221	down_read(&ubi->fm_eba_sem);
222	spin_lock(&ubi->wl_lock);
223	}
224
225	if (pool->used == pool->size) {
226	spin_unlock(&ubi->wl_lock);
227	if (retried) {
228	ubi_err(ubi, "Unable to get a free PEB from user WL pool");
229	ret = -ENOSPC;
230	goto out;
231	}
232	retried = 1;
233	up_read(&ubi->fm_eba_sem);
234	goto again;
235	}
236
237	ubi_assert(pool->used < pool->size);
238	ret = pool->pebs[pool->used++];
239	prot_queue_add(ubi, ubi->lookuptbl[ret]);
240	spin_unlock(&ubi->wl_lock);
241	out:
242	return ret;
243	}
244
245	/* get_peb_for_wl - returns a PEB to be used internally by the WL sub-system.
246	*
247	* @ubi: UBI device description object
248	*/
249	static struct ubi_wl_entry get_peb_for_wl(struct ubi_device ubi)
250	{
251	struct ubi_fm_pool *pool = &ubi->fm_wl_pool;
252	int pnum;
253
254	if (pool->used == pool->size) {
255	/* We cannot update the fastmap here because this
256	* function is called in atomic context.
257	* Let's fail here and refill/update it as soon as possible. */
258	if (!ubi->fm_work_scheduled) {
259	ubi->fm_work_scheduled = 1;
260	schedule_work(&ubi->fm_work);
261	}
262	return NULL;
78d6d497	263	}
e1bc37ce RW	264
	265	pnum = pool->pebs[pool->used++];
	266	return ubi->lookuptbl[pnum];
78d6d497 RW	267	}
	268
	269	/**
	270	* ubi_ensure_anchor_pebs - schedule wear-leveling to produce an anchor PEB.
	271	* @ubi: UBI device description object
	272	*/
	273	int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
	274	{
	275	struct ubi_work *wrk;
	276
	277	spin_lock(&ubi->wl_lock);
	278	if (ubi->wl_scheduled) {
	279	spin_unlock(&ubi->wl_lock);
	280	return 0;
	281	}
	282	ubi->wl_scheduled = 1;
	283	spin_unlock(&ubi->wl_lock);
	284
	285	wrk = kmalloc(sizeof(struct ubi_work), GFP_NOFS);
	286	if (!wrk) {
	287	spin_lock(&ubi->wl_lock);
	288	ubi->wl_scheduled = 0;
	289	spin_unlock(&ubi->wl_lock);
	290	return -ENOMEM;
	291	}
	292
	293	wrk->anchor = 1;
	294	wrk->func = &wear_leveling_worker;
	295	schedule_ubi_work(ubi, wrk);
	296	return 0;
	297	}
	298
	299	/**
	300	* ubi_wl_put_fm_peb - returns a PEB used in a fastmap to the wear-leveling
	301	* sub-system.
	302	* see: ubi_wl_put_peb()
	303	*
	304	* @ubi: UBI device description object
	305	* @fm_e: physical eraseblock to return
	306	* @lnum: the last used logical eraseblock number for the PEB
	307	* @torture: if this physical eraseblock has to be tortured
	308	*/
	309	int ubi_wl_put_fm_peb(struct ubi_device ubi, struct ubi_wl_entry fm_e,
	310	int lnum, int torture)
	311	{
	312	struct ubi_wl_entry *e;
	313	int vol_id, pnum = fm_e->pnum;
	314
	315	dbg_wl("PEB %d", pnum);
	316
	317	ubi_assert(pnum >= 0);
	318	ubi_assert(pnum < ubi->peb_count);
	319
	320	spin_lock(&ubi->wl_lock);
	321	e = ubi->lookuptbl[pnum];
	322
	323	/* This can happen if we recovered from a fastmap the very
	324	* first time and writing now a new one. In this case the wl system
	325	* has never seen any PEB used by the original fastmap.
	326	*/
	327	if (!e) {
	328	e = fm_e;
	329	ubi_assert(e->ec >= 0);
	330	ubi->lookuptbl[pnum] = e;
331	}
332
333	spin_unlock(&ubi->wl_lock);
334
335	vol_id = lnum ? UBI_FM_DATA_VOLUME_ID : UBI_FM_SB_VOLUME_ID;
336	return schedule_erase(ubi, e, vol_id, lnum, torture);
337	}
338
339	/**
340	* ubi_is_erase_work - checks whether a work is erase work.
341	* @wrk: The work object to be checked
342	*/
343	int ubi_is_erase_work(struct ubi_work *wrk)
344	{
345	return wrk->func == erase_worker;
346	}
347
348	static void ubi_fastmap_close(struct ubi_device *ubi)
349	{
350	int i;
351
352	flush_work(&ubi->fm_work);
353	return_unused_pool_pebs(ubi, &ubi->fm_pool);
354	return_unused_pool_pebs(ubi, &ubi->fm_wl_pool);
355
356	if (ubi->fm) {
357	for (i = 0; i < ubi->fm->used_blocks; i++)
358	kfree(ubi->fm->e[i]);
359	}
360	kfree(ubi->fm);
361	}
2f84c246 RW	362
	363	/**
	364	* may_reserve_for_fm - tests whether a PEB shall be reserved for fastmap.
	365	* See find_mean_wl_entry()
	366	*
	367	* @ubi: UBI device description object
	368	* @e: physical eraseblock to return
	369	* @root: RB tree to test against.
	370	*/
	371	static struct ubi_wl_entry may_reserve_for_fm(struct ubi_device ubi,
	372	struct ubi_wl_entry *e,
	373	struct rb_root *root) {
	374	if (e && !ubi->fm_disabled && !ubi->fm &&
	375	e->pnum < UBI_FM_MAX_START)
	376	e = rb_entry(rb_next(root->rb_node),
	377	struct ubi_wl_entry, u.rb);
	378
	379	return e;
	380	}