/*
   * Copyright (C) 2016 Facebook
   * Copyright (C) 2013-2014 Jens Axboe
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License v2 as published by the Free Software Foundation.
   *
   * 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.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program.  If not, see <https://www.gnu.org/licenses/>.
   */

  #include <linux/sched.h>

  #include <linux/random.h>

  #include <linux/sbitmap.h>

  #include <linux/seq_file.h>

  
  int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
  		      gfp_t flags, int node)
  {
  	unsigned int bits_per_word;
  	unsigned int i;
  
  	if (shift < 0) {
  		shift = ilog2(BITS_PER_LONG);
  		/*
  		 * If the bitmap is small, shrink the number of bits per word so
  		 * we spread over a few cachelines, at least. If less than 4
  		 * bits, just forget about it, it's not going to work optimally
  		 * anyway.
  		 */
  		if (depth >= 4) {
  			while ((4U << shift) > depth)
  				shift--;
  		}
  	}
  	bits_per_word = 1U << shift;
  	if (bits_per_word > BITS_PER_LONG)
  		return -EINVAL;
  
  	sb->shift = shift;
  	sb->depth = depth;
  	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  
  	if (depth == 0) {
  		sb->map = NULL;
  		return 0;
  	}

  	sb->map = kcalloc_node(sb->map_nr, sizeof(*sb->map), flags, node);

  	if (!sb->map)
  		return -ENOMEM;
  
  	for (i = 0; i < sb->map_nr; i++) {
  		sb->map[i].depth = min(depth, bits_per_word);
  		depth -= sb->map[i].depth;
  	}
  	return 0;
  }
  EXPORT_SYMBOL_GPL(sbitmap_init_node);
  
  void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
  {
  	unsigned int bits_per_word = 1U << sb->shift;
  	unsigned int i;
  
  	sb->depth = depth;
  	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  
  	for (i = 0; i < sb->map_nr; i++) {
  		sb->map[i].depth = min(depth, bits_per_word);
  		depth -= sb->map[i].depth;
  	}
  }
  EXPORT_SYMBOL_GPL(sbitmap_resize);

  static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
  			      unsigned int hint, bool wrap)

  {
  	unsigned int orig_hint = hint;
  	int nr;
  
  	while (1) {

  		nr = find_next_zero_bit(word, depth, hint);
  		if (unlikely(nr >= depth)) {

  			/*
  			 * We started with an offset, and we didn't reset the
  			 * offset to 0 in a failure case, so start from 0 to
  			 * exhaust the map.
  			 */
  			if (orig_hint && hint && wrap) {
  				hint = orig_hint = 0;
  				continue;
  			}
  			return -1;
  		}

  		if (!test_and_set_bit_lock(nr, word))

  			break;
  
  		hint = nr + 1;

  		if (hint >= depth - 1)

  			hint = 0;
  	}
  
  	return nr;
  }
  
  int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
  {
  	unsigned int i, index;
  	int nr = -1;
  
  	index = SB_NR_TO_INDEX(sb, alloc_hint);
  
  	for (i = 0; i < sb->map_nr; i++) {

  		nr = __sbitmap_get_word(&sb->map[index].word,
  					sb->map[index].depth,

  					SB_NR_TO_BIT(sb, alloc_hint),
  					!round_robin);
  		if (nr != -1) {
  			nr += index << sb->shift;
  			break;
  		}
  
  		/* Jump to next index. */
  		index++;
  		alloc_hint = index << sb->shift;
  
  		if (index >= sb->map_nr) {
  			index = 0;
  			alloc_hint = 0;
  		}
  	}
  
  	return nr;
  }
  EXPORT_SYMBOL_GPL(sbitmap_get);

  int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
  			unsigned long shallow_depth)
  {
  	unsigned int i, index;
  	int nr = -1;
  
  	index = SB_NR_TO_INDEX(sb, alloc_hint);
  
  	for (i = 0; i < sb->map_nr; i++) {
  		nr = __sbitmap_get_word(&sb->map[index].word,
  					min(sb->map[index].depth, shallow_depth),
  					SB_NR_TO_BIT(sb, alloc_hint), true);
  		if (nr != -1) {
  			nr += index << sb->shift;
  			break;
  		}
  
  		/* Jump to next index. */
  		index++;
  		alloc_hint = index << sb->shift;
  
  		if (index >= sb->map_nr) {
  			index = 0;
  			alloc_hint = 0;
  		}
  	}
  
  	return nr;
  }
  EXPORT_SYMBOL_GPL(sbitmap_get_shallow);

  bool sbitmap_any_bit_set(const struct sbitmap *sb)
  {
  	unsigned int i;
  
  	for (i = 0; i < sb->map_nr; i++) {
  		if (sb->map[i].word)
  			return true;
  	}
  	return false;
  }
  EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
  
  bool sbitmap_any_bit_clear(const struct sbitmap *sb)
  {
  	unsigned int i;
  
  	for (i = 0; i < sb->map_nr; i++) {
  		const struct sbitmap_word *word = &sb->map[i];
  		unsigned long ret;
  
  		ret = find_first_zero_bit(&word->word, word->depth);
  		if (ret < word->depth)
  			return true;
  	}
  	return false;
  }
  EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
  
  unsigned int sbitmap_weight(const struct sbitmap *sb)
  {

  	unsigned int i, weight = 0;

  
  	for (i = 0; i < sb->map_nr; i++) {
  		const struct sbitmap_word *word = &sb->map[i];
  
  		weight += bitmap_weight(&word->word, word->depth);
  	}
  	return weight;
  }
  EXPORT_SYMBOL_GPL(sbitmap_weight);

  void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
  {
  	seq_printf(m, "depth=%u
  ", sb->depth);
  	seq_printf(m, "busy=%u
  ", sbitmap_weight(sb));
  	seq_printf(m, "bits_per_word=%u
  ", 1U << sb->shift);
  	seq_printf(m, "map_nr=%u
  ", sb->map_nr);
  }
  EXPORT_SYMBOL_GPL(sbitmap_show);
  
  static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
  {
  	if ((offset & 0xf) == 0) {
  		if (offset != 0)
  			seq_putc(m, '
  ');
  		seq_printf(m, "%08x:", offset);
  	}
  	if ((offset & 0x1) == 0)
  		seq_putc(m, ' ');
  	seq_printf(m, "%02x", byte);
  }
  
  void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
  {
  	u8 byte = 0;
  	unsigned int byte_bits = 0;
  	unsigned int offset = 0;
  	int i;
  
  	for (i = 0; i < sb->map_nr; i++) {
  		unsigned long word = READ_ONCE(sb->map[i].word);
  		unsigned int word_bits = READ_ONCE(sb->map[i].depth);
  
  		while (word_bits > 0) {
  			unsigned int bits = min(8 - byte_bits, word_bits);
  
  			byte |= (word & (BIT(bits) - 1)) << byte_bits;
  			byte_bits += bits;
  			if (byte_bits == 8) {
  				emit_byte(m, offset, byte);
  				byte = 0;
  				byte_bits = 0;
  				offset++;
  			}
  			word >>= bits;
  			word_bits -= bits;
  		}
  	}
  	if (byte_bits) {
  		emit_byte(m, offset, byte);
  		offset++;
  	}
  	if (offset)
  		seq_putc(m, '
  ');
  }
  EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);

  static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
  					unsigned int depth)

  {
  	unsigned int wake_batch;

  	unsigned int shallow_depth;

  
  	/*
  	 * For each batch, we wake up one queue. We need to make sure that our

  	 * batch size is small enough that the full depth of the bitmap,
  	 * potentially limited by a shallow depth, is enough to wake up all of
  	 * the queues.
  	 *
  	 * Each full word of the bitmap has bits_per_word bits, and there might
  	 * be a partial word. There are depth / bits_per_word full words and
  	 * depth % bits_per_word bits left over. In bitwise arithmetic:
  	 *
  	 * bits_per_word = 1 << shift
  	 * depth / bits_per_word = depth >> shift
  	 * depth % bits_per_word = depth & ((1 << shift) - 1)
  	 *
  	 * Each word can be limited to sbq->min_shallow_depth bits.

  	 */

  	shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
  	depth = ((depth >> sbq->sb.shift) * shallow_depth +
  		 min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
  	wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
  			     SBQ_WAKE_BATCH);

  
  	return wake_batch;
  }
  
  int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,

  			    int shift, bool round_robin, gfp_t flags, int node)

  {
  	int ret;
  	int i;
  
  	ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
  	if (ret)
  		return ret;

  	sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
  	if (!sbq->alloc_hint) {
  		sbitmap_free(&sbq->sb);
  		return -ENOMEM;
  	}

  	if (depth && !round_robin) {
  		for_each_possible_cpu(i)
  			*per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
  	}

  	sbq->min_shallow_depth = UINT_MAX;
  	sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);

  	atomic_set(&sbq->wake_index, 0);

  	sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);

  	if (!sbq->ws) {

  		free_percpu(sbq->alloc_hint);

  		sbitmap_free(&sbq->sb);
  		return -ENOMEM;
  	}
  
  	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
  		init_waitqueue_head(&sbq->ws[i].wait);
  		atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
  	}

  
  	sbq->round_robin = round_robin;

  	return 0;
  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);

  static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
  					    unsigned int depth)

  {

  	unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);

  	int i;
  
  	if (sbq->wake_batch != wake_batch) {
  		WRITE_ONCE(sbq->wake_batch, wake_batch);
  		/*

  		 * Pairs with the memory barrier in sbitmap_queue_wake_up()
  		 * to ensure that the batch size is updated before the wait
  		 * counts.

  		 */
  		smp_mb__before_atomic();
  		for (i = 0; i < SBQ_WAIT_QUEUES; i++)
  			atomic_set(&sbq->ws[i].wait_cnt, 1);
  	}

  }
  
  void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
  {
  	sbitmap_queue_update_wake_batch(sbq, depth);

  	sbitmap_resize(&sbq->sb, depth);
  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_resize);

  int __sbitmap_queue_get(struct sbitmap_queue *sbq)

  {

  	unsigned int hint, depth;

  	int nr;
  
  	hint = this_cpu_read(*sbq->alloc_hint);

  	depth = READ_ONCE(sbq->sb.depth);
  	if (unlikely(hint >= depth)) {
  		hint = depth ? prandom_u32() % depth : 0;
  		this_cpu_write(*sbq->alloc_hint, hint);
  	}

  	nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);

  
  	if (nr == -1) {
  		/* If the map is full, a hint won't do us much good. */
  		this_cpu_write(*sbq->alloc_hint, 0);

  	} else if (nr == hint || unlikely(sbq->round_robin)) {

  		/* Only update the hint if we used it. */
  		hint = nr + 1;

  		if (hint >= depth - 1)

  			hint = 0;
  		this_cpu_write(*sbq->alloc_hint, hint);
  	}
  
  	return nr;
  }
  EXPORT_SYMBOL_GPL(__sbitmap_queue_get);

  int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
  				unsigned int shallow_depth)
  {
  	unsigned int hint, depth;
  	int nr;

  	WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);

  	hint = this_cpu_read(*sbq->alloc_hint);
  	depth = READ_ONCE(sbq->sb.depth);
  	if (unlikely(hint >= depth)) {
  		hint = depth ? prandom_u32() % depth : 0;
  		this_cpu_write(*sbq->alloc_hint, hint);
  	}
  	nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
  
  	if (nr == -1) {
  		/* If the map is full, a hint won't do us much good. */
  		this_cpu_write(*sbq->alloc_hint, 0);
  	} else if (nr == hint || unlikely(sbq->round_robin)) {
  		/* Only update the hint if we used it. */
  		hint = nr + 1;
  		if (hint >= depth - 1)
  			hint = 0;
  		this_cpu_write(*sbq->alloc_hint, hint);
  	}
  
  	return nr;
  }
  EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);

  void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
  				     unsigned int min_shallow_depth)
  {
  	sbq->min_shallow_depth = min_shallow_depth;
  	sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);

  static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
  {
  	int i, wake_index;
  
  	wake_index = atomic_read(&sbq->wake_index);
  	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
  		struct sbq_wait_state *ws = &sbq->ws[wake_index];
  
  		if (waitqueue_active(&ws->wait)) {
  			int o = atomic_read(&sbq->wake_index);
  
  			if (wake_index != o)
  				atomic_cmpxchg(&sbq->wake_index, o, wake_index);
  			return ws;
  		}
  
  		wake_index = sbq_index_inc(wake_index);
  	}
  
  	return NULL;
  }

  static bool __sbq_wake_up(struct sbitmap_queue *sbq)

  {
  	struct sbq_wait_state *ws;

  	unsigned int wake_batch;

  	int wait_cnt;

  	ws = sbq_wake_ptr(sbq);
  	if (!ws)

  		return false;

  
  	wait_cnt = atomic_dec_return(&ws->wait_cnt);

  	if (wait_cnt <= 0) {

  		int ret;

  		wake_batch = READ_ONCE(sbq->wake_batch);

  		/*
  		 * Pairs with the memory barrier in sbitmap_queue_resize() to
  		 * ensure that we see the batch size update before the wait
  		 * count is reset.
  		 */
  		smp_mb__before_atomic();

  		/*

  		 * For concurrent callers of this, the one that failed the
  		 * atomic_cmpxhcg() race should call this function again
  		 * to wakeup a new batch on a different 'ws'.

  		 */

  		ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
  		if (ret == wait_cnt) {
  			sbq_index_atomic_inc(&sbq->wake_index);
  			wake_up_nr(&ws->wait, wake_batch);
  			return false;
  		}
  
  		return true;

  	}

  
  	return false;
  }

  void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)

  {
  	while (__sbq_wake_up(sbq))
  		;

  }

  EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);

  void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,

  			 unsigned int cpu)

  {

  	sbitmap_clear_bit_unlock(&sbq->sb, nr);

  	/*
  	 * Pairs with the memory barrier in set_current_state() to ensure the
  	 * proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
  	 * and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
  	 * waiter. See the comment on waitqueue_active().
  	 */
  	smp_mb__after_atomic();
  	sbitmap_queue_wake_up(sbq);

  	if (likely(!sbq->round_robin && nr < sbq->sb.depth))

  		*per_cpu_ptr(sbq->alloc_hint, cpu) = nr;

  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
  
  void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
  {
  	int i, wake_index;
  
  	/*

  	 * Pairs with the memory barrier in set_current_state() like in

  	 * sbitmap_queue_wake_up().

  	 */
  	smp_mb();
  	wake_index = atomic_read(&sbq->wake_index);
  	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
  		struct sbq_wait_state *ws = &sbq->ws[wake_index];
  
  		if (waitqueue_active(&ws->wait))
  			wake_up(&ws->wait);
  
  		wake_index = sbq_index_inc(wake_index);
  	}
  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);

  
  void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
  {
  	bool first;
  	int i;
  
  	sbitmap_show(&sbq->sb, m);
  
  	seq_puts(m, "alloc_hint={");
  	first = true;
  	for_each_possible_cpu(i) {
  		if (!first)
  			seq_puts(m, ", ");
  		first = false;
  		seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
  	}
  	seq_puts(m, "}
  ");
  
  	seq_printf(m, "wake_batch=%u
  ", sbq->wake_batch);
  	seq_printf(m, "wake_index=%d
  ", atomic_read(&sbq->wake_index));
  
  	seq_puts(m, "ws={
  ");
  	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
  		struct sbq_wait_state *ws = &sbq->ws[i];
  
  		seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},
  ",
  			   atomic_read(&ws->wait_cnt),
  			   waitqueue_active(&ws->wait) ? "active" : "inactive");
  	}
  	seq_puts(m, "}
  ");
  
  	seq_printf(m, "round_robin=%d
  ", sbq->round_robin);

  	seq_printf(m, "min_shallow_depth=%u
  ", sbq->min_shallow_depth);

  }
  EXPORT_SYMBOL_GPL(sbitmap_queue_show);