text: /*
   * tracing_map - lock-free map for tracing
   *
   * 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; either version 2 of the License, or
   * (at your option) any later version.
   *
   * 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.
   *
   * Copyright (C) 2015 Tom Zanussi <tom.zanussi@linux.intel.com>
   *
   * tracing_map implementation inspired by lock-free map algorithms
   * originated by Dr. Cliff Click:
   *
   * http://www.azulsystems.com/blog/cliff/2007-03-26-non-blocking-hashtable
   * http://www.azulsystems.com/events/javaone_2007/2007_LockFreeHash.pdf
   */
  
  #include <linux/vmalloc.h>
  #include <linux/jhash.h>
  #include <linux/slab.h>
  #include <linux/sort.h>
  
  #include "tracing_map.h"
  #include "trace.h"
  
  /*
   * NOTE: For a detailed description of the data structures used by
   * these functions (such as tracing_map_elt) please see the overview
   * of tracing_map data structures at the beginning of tracing_map.h.
   */
  
  /**
   * tracing_map_update_sum - Add a value to a tracing_map_elt's sum field
   * @elt: The tracing_map_elt
   * @i: The index of the given sum associated with the tracing_map_elt
   * @n: The value to add to the sum
   *
   * Add n to sum i associated with the specified tracing_map_elt
   * instance.  The index i is the index returned by the call to
   * tracing_map_add_sum_field() when the tracing map was set up.
   */
  void tracing_map_update_sum(struct tracing_map_elt *elt, unsigned int i, u64 n)
  {
  	atomic64_add(n, &elt->fields[i].sum);
  }
  
  /**
   * tracing_map_read_sum - Return the value of a tracing_map_elt's sum field
   * @elt: The tracing_map_elt
   * @i: The index of the given sum associated with the tracing_map_elt
   *
   * Retrieve the value of the sum i associated with the specified
   * tracing_map_elt instance.  The index i is the index returned by the
   * call to tracing_map_add_sum_field() when the tracing map was set
   * up.
   *
   * Return: The sum associated with field i for elt.
   */
  u64 tracing_map_read_sum(struct tracing_map_elt *elt, unsigned int i)
  {
  	return (u64)atomic64_read(&elt->fields[i].sum);
  }
  
  int tracing_map_cmp_string(void *val_a, void *val_b)
  {
  	char *a = val_a;
  	char *b = val_b;
  
  	return strcmp(a, b);
  }
  
  int tracing_map_cmp_none(void *val_a, void *val_b)
  {
  	return 0;
  }
  
  static int tracing_map_cmp_atomic64(void *val_a, void *val_b)
  {
  	u64 a = atomic64_read((atomic64_t *)val_a);
  	u64 b = atomic64_read((atomic64_t *)val_b);
  
  	return (a > b) ? 1 : ((a < b) ? -1 : 0);
  }
  
  #define DEFINE_TRACING_MAP_CMP_FN(type)					\
  static int tracing_map_cmp_##type(void *val_a, void *val_b)		\
  {									\
  	type a = (type)(*(u64 *)val_a);					\
  	type b = (type)(*(u64 *)val_b);					\
  									\
  	return (a > b) ? 1 : ((a < b) ? -1 : 0);			\
  }
  
  DEFINE_TRACING_MAP_CMP_FN(s64);
  DEFINE_TRACING_MAP_CMP_FN(u64);
  DEFINE_TRACING_MAP_CMP_FN(s32);
  DEFINE_TRACING_MAP_CMP_FN(u32);
  DEFINE_TRACING_MAP_CMP_FN(s16);
  DEFINE_TRACING_MAP_CMP_FN(u16);
  DEFINE_TRACING_MAP_CMP_FN(s8);
  DEFINE_TRACING_MAP_CMP_FN(u8);
  
  tracing_map_cmp_fn_t tracing_map_cmp_num(int field_size,
  					 int field_is_signed)
  {
  	tracing_map_cmp_fn_t fn = tracing_map_cmp_none;
  
  	switch (field_size) {
  	case 8:
  		if (field_is_signed)
  			fn = tracing_map_cmp_s64;
  		else
  			fn = tracing_map_cmp_u64;
  		break;
  	case 4:
  		if (field_is_signed)
  			fn = tracing_map_cmp_s32;
  		else
  			fn = tracing_map_cmp_u32;
  		break;
  	case 2:
  		if (field_is_signed)
  			fn = tracing_map_cmp_s16;
  		else
  			fn = tracing_map_cmp_u16;
  		break;
  	case 1:
  		if (field_is_signed)
  			fn = tracing_map_cmp_s8;
  		else
  			fn = tracing_map_cmp_u8;
  		break;
  	}
  
  	return fn;
  }
  
  static int tracing_map_add_field(struct tracing_map *map,
  				 tracing_map_cmp_fn_t cmp_fn)
  {
  	int ret = -EINVAL;
  
  	if (map->n_fields < TRACING_MAP_FIELDS_MAX) {
  		ret = map->n_fields;
  		map->fields[map->n_fields++].cmp_fn = cmp_fn;
  	}
  
  	return ret;
  }
  
  /**
   * tracing_map_add_sum_field - Add a field describing a tracing_map sum
   * @map: The tracing_map
   *
   * Add a sum field to the key and return the index identifying it in
   * the map and associated tracing_map_elts.  This is the index used
   * for instance to update a sum for a particular tracing_map_elt using
   * tracing_map_update_sum() or reading it via tracing_map_read_sum().
   *
   * Return: The index identifying the field in the map and associated
   * tracing_map_elts, or -EINVAL on error.
   */
  int tracing_map_add_sum_field(struct tracing_map *map)
  {
  	return tracing_map_add_field(map, tracing_map_cmp_atomic64);
  }
  
  /**
   * tracing_map_add_key_field - Add a field describing a tracing_map key
   * @map: The tracing_map
   * @offset: The offset within the key
   * @cmp_fn: The comparison function that will be used to sort on the key
   *
   * Let the map know there is a key and that if it's used as a sort key
   * to use cmp_fn.
   *
   * A key can be a subset of a compound key; for that purpose, the
   * offset param is used to describe where within the the compound key
   * the key referenced by this key field resides.
   *
   * Return: The index identifying the field in the map and associated
   * tracing_map_elts, or -EINVAL on error.
   */
  int tracing_map_add_key_field(struct tracing_map *map,
  			      unsigned int offset,
  			      tracing_map_cmp_fn_t cmp_fn)
  
  {
  	int idx = tracing_map_add_field(map, cmp_fn);
  
  	if (idx < 0)
  		return idx;
  
  	map->fields[idx].offset = offset;
  
  	map->key_idx[map->n_keys++] = idx;
  
  	return idx;
  }
  
  void tracing_map_array_clear(struct tracing_map_array *a)
  {
  	unsigned int i;
  
  	if (!a->pages)
  		return;
  
  	for (i = 0; i < a->n_pages; i++)
  		memset(a->pages[i], 0, PAGE_SIZE);
  }
  
  void tracing_map_array_free(struct tracing_map_array *a)
  {
  	unsigned int i;
  
  	if (!a)
  		return;
  
  	if (!a->pages)
  		goto free;
  
  	for (i = 0; i < a->n_pages; i++) {
  		if (!a->pages[i])
  			break;
  		free_page((unsigned long)a->pages[i]);
  	}
  
  	kfree(a->pages);
  
   free:
  	kfree(a);
  }
  
  struct tracing_map_array *tracing_map_array_alloc(unsigned int n_elts,
  						  unsigned int entry_size)
  {
  	struct tracing_map_array *a;
  	unsigned int i;
  
  	a = kzalloc(sizeof(*a), GFP_KERNEL);
  	if (!a)
  		return NULL;
  
  	a->entry_size_shift = fls(roundup_pow_of_two(entry_size) - 1);
  	a->entries_per_page = PAGE_SIZE / (1 << a->entry_size_shift);
  	a->n_pages = n_elts / a->entries_per_page;
  	if (!a->n_pages)
  		a->n_pages = 1;
  	a->entry_shift = fls(a->entries_per_page) - 1;
  	a->entry_mask = (1 << a->entry_shift) - 1;
  
  	a->pages = kcalloc(a->n_pages, sizeof(void *), GFP_KERNEL);
  	if (!a->pages)
  		goto free;
  
  	for (i = 0; i < a->n_pages; i++) {
  		a->pages[i] = (void *)get_zeroed_page(GFP_KERNEL);
  		if (!a->pages[i])
  			goto free;
  	}
   out:
  	return a;
   free:
  	tracing_map_array_free(a);
  	a = NULL;
  
  	goto out;
  }
  
  static void tracing_map_elt_clear(struct tracing_map_elt *elt)
  {
  	unsigned i;
  
  	for (i = 0; i < elt->map->n_fields; i++)
  		if (elt->fields[i].cmp_fn == tracing_map_cmp_atomic64)
  			atomic64_set(&elt->fields[i].sum, 0);
  
  	if (elt->map->ops && elt->map->ops->elt_clear)
  		elt->map->ops->elt_clear(elt);
  }
  
  static void tracing_map_elt_init_fields(struct tracing_map_elt *elt)
  {
  	unsigned int i;
  
  	tracing_map_elt_clear(elt);
  
  	for (i = 0; i < elt->map->n_fields; i++) {
  		elt->fields[i].cmp_fn = elt->map->fields[i].cmp_fn;
  
  		if (elt->fields[i].cmp_fn != tracing_map_cmp_atomic64)
  			elt->fields[i].offset = elt->map->fields[i].offset;
  	}
  }
  
  static void tracing_map_elt_free(struct tracing_map_elt *elt)
  {
  	if (!elt)
  		return;
  
  	if (elt->map->ops && elt->map->ops->elt_free)
  		elt->map->ops->elt_free(elt);
  	kfree(elt->fields);
  	kfree(elt->key);
  	kfree(elt);
  }
  
  static struct tracing_map_elt *tracing_map_elt_alloc(struct tracing_map *map)
  {
  	struct tracing_map_elt *elt;
  	int err = 0;
  
  	elt = kzalloc(sizeof(*elt), GFP_KERNEL);
  	if (!elt)
  		return ERR_PTR(-ENOMEM);
  
  	elt->map = map;
  
  	elt->key = kzalloc(map->key_size, GFP_KERNEL);
  	if (!elt->key) {
  		err = -ENOMEM;
  		goto free;
  	}
  
  	elt->fields = kcalloc(map->n_fields, sizeof(*elt->fields), GFP_KERNEL);
  	if (!elt->fields) {
  		err = -ENOMEM;
  		goto free;
  	}
  
  	tracing_map_elt_init_fields(elt);
  
  	if (map->ops && map->ops->elt_alloc) {
  		err = map->ops->elt_alloc(elt);
  		if (err)
  			goto free;
  	}
  	return elt;
   free:
  	tracing_map_elt_free(elt);
  
  	return ERR_PTR(err);
  }
  
  static struct tracing_map_elt *get_free_elt(struct tracing_map *map)
  {
  	struct tracing_map_elt *elt = NULL;
  	int idx;
  
  	idx = atomic_inc_return(&map->next_elt);
  	if (idx < map->max_elts) {
  		elt = *(TRACING_MAP_ELT(map->elts, idx));
  		if (map->ops && map->ops->elt_init)
  			map->ops->elt_init(elt);
  	}
  
  	return elt;
  }
  
  static void tracing_map_free_elts(struct tracing_map *map)
  {
  	unsigned int i;
  
  	if (!map->elts)
  		return;
  
  	for (i = 0; i < map->max_elts; i++) {
  		tracing_map_elt_free(*(TRACING_MAP_ELT(map->elts, i)));
  		*(TRACING_MAP_ELT(map->elts, i)) = NULL;
  	}
  
  	tracing_map_array_free(map->elts);
  	map->elts = NULL;
  }
  
  static int tracing_map_alloc_elts(struct tracing_map *map)
  {
  	unsigned int i;
  
  	map->elts = tracing_map_array_alloc(map->max_elts,
  					    sizeof(struct tracing_map_elt *));
  	if (!map->elts)
  		return -ENOMEM;
  
  	for (i = 0; i < map->max_elts; i++) {
  		*(TRACING_MAP_ELT(map->elts, i)) = tracing_map_elt_alloc(map);
  		if (IS_ERR(*(TRACING_MAP_ELT(map->elts, i)))) {
  			*(TRACING_MAP_ELT(map->elts, i)) = NULL;
  			tracing_map_free_elts(map);
  
  			return -ENOMEM;
  		}
  	}
  
  	return 0;
  }
  
  static inline bool keys_match(void *key, void *test_key, unsigned key_size)
  {
  	bool match = true;
  
  	if (memcmp(key, test_key, key_size))
  		match = false;
  
  	return match;
  }
  
  static inline struct tracing_map_elt *
  __tracing_map_insert(struct tracing_map *map, void *key, bool lookup_only)
  {
  	u32 idx, key_hash, test_key;
  	struct tracing_map_entry *entry;
  
  	key_hash = jhash(key, map->key_size, 0);
  	if (key_hash == 0)
  		key_hash = 1;
  	idx = key_hash >> (32 - (map->map_bits + 1));
  
  	while (1) {
  		idx &= (map->map_size - 1);
  		entry = TRACING_MAP_ENTRY(map->map, idx);
  		test_key = entry->key;
  
  		if (test_key && test_key == key_hash && entry->val &&
  		    keys_match(key, entry->val->key, map->key_size)) {
  			atomic64_inc(&map->hits);
  			return entry->val;
  		}
  
  		if (!test_key) {
  			if (lookup_only)
  				break;
  
  			if (!cmpxchg(&entry->key, 0, key_hash)) {
  				struct tracing_map_elt *elt;
  
  				elt = get_free_elt(map);
  				if (!elt) {
  					atomic64_inc(&map->drops);
  					entry->key = 0;
  					break;
  				}
  
  				memcpy(elt->key, key, map->key_size);
  				entry->val = elt;
  				atomic64_inc(&map->hits);
  
  				return entry->val;
  			}
  		}
  
  		idx++;
  	}
  
  	return NULL;
  }
  
  /**
   * tracing_map_insert - Insert key and/or retrieve val from a tracing_map
   * @map: The tracing_map to insert into
   * @key: The key to insert
   *
   * Inserts a key into a tracing_map and creates and returns a new
   * tracing_map_elt for it, or if the key has already been inserted by
   * a previous call, returns the tracing_map_elt already associated
   * with it.  When the map was created, the number of elements to be
   * allocated for the map was specified (internally maintained as
   * 'max_elts' in struct tracing_map), and that number of
   * tracing_map_elts was created by tracing_map_init().  This is the
   * pre-allocated pool of tracing_map_elts that tracing_map_insert()
   * will allocate from when adding new keys.  Once that pool is
   * exhausted, tracing_map_insert() is useless and will return NULL to
   * signal that state.  There are two user-visible tracing_map
   * variables, 'hits' and 'drops', which are updated by this function.
   * Every time an element is either successfully inserted or retrieved,
   * the 'hits' value is incrememented.  Every time an element insertion
   * fails, the 'drops' value is incremented.
   *
   * This is a lock-free tracing map insertion function implementing a
   * modified form of Cliff Click's basic insertion algorithm.  It
   * requires the table size be a power of two.  To prevent any
   * possibility of an infinite loop we always make the internal table
   * size double the size of the requested table size (max_elts * 2).
   * Likewise, we never reuse a slot or resize or delete elements - when
   * we've reached max_elts entries, we simply return NULL once we've
   * run out of entries.  Readers can at any point in time traverse the
   * tracing map and safely access the key/val pairs.
   *
   * Return: the tracing_map_elt pointer val associated with the key.
   * If this was a newly inserted key, the val will be a newly allocated
   * and associated tracing_map_elt pointer val.  If the key wasn't
   * found and the pool of tracing_map_elts has been exhausted, NULL is
   * returned and no further insertions will succeed.
   */
  struct tracing_map_elt *tracing_map_insert(struct tracing_map *map, void *key)
  {
  	return __tracing_map_insert(map, key, false);
  }
  
  /**
   * tracing_map_lookup - Retrieve val from a tracing_map
   * @map: The tracing_map to perform the lookup on
   * @key: The key to look up
   *
   * Looks up key in tracing_map and if found returns the matching
   * tracing_map_elt.  This is a lock-free lookup; see
   * tracing_map_insert() for details on tracing_map and how it works.
   * Every time an element is retrieved, the 'hits' value is
   * incrememented.  There is one user-visible tracing_map variable,
   * 'hits', which is updated by this function.  Every time an element
   * is successfully retrieved, the 'hits' value is incrememented.  The
   * 'drops' value is never updated by this function.
   *
   * Return: the tracing_map_elt pointer val associated with the key.
   * If the key wasn't found, NULL is returned.
   */
  struct tracing_map_elt *tracing_map_lookup(struct tracing_map *map, void *key)
  {
  	return __tracing_map_insert(map, key, true);
  }
  
  /**
   * tracing_map_destroy - Destroy a tracing_map
   * @map: The tracing_map to destroy
   *
   * Frees a tracing_map along with its associated array of
   * tracing_map_elts.
   *
   * Callers should make sure there are no readers or writers actively
   * reading or inserting into the map before calling this.
   */
  void tracing_map_destroy(struct tracing_map *map)
  {
  	if (!map)
  		return;
  
  	tracing_map_free_elts(map);
  
  	tracing_map_array_free(map->map);
  	kfree(map);
  }
  
  /**
   * tracing_map_clear - Clear a tracing_map
   * @map: The tracing_map to clear
   *
   * Resets the tracing map to a cleared or initial state.  The
   * tracing_map_elts are all cleared, and the array of struct
   * tracing_map_entry is reset to an initialized state.
   *
   * Callers should make sure there are no writers actively inserting
   * into the map before calling this.
   */
  void tracing_map_clear(struct tracing_map *map)
  {
  	unsigned int i;
  
  	atomic_set(&map->next_elt, -1);
  	atomic64_set(&map->hits, 0);
  	atomic64_set(&map->drops, 0);
  
  	tracing_map_array_clear(map->map);
  
  	for (i = 0; i < map->max_elts; i++)
  		tracing_map_elt_clear(*(TRACING_MAP_ELT(map->elts, i)));
  }
  
  static void set_sort_key(struct tracing_map *map,
  			 struct tracing_map_sort_key *sort_key)
  {
  	map->sort_key = *sort_key;
  }
  
  /**
   * tracing_map_create - Create a lock-free map and element pool
   * @map_bits: The size of the map (2 ** map_bits)
   * @key_size: The size of the key for the map in bytes
   * @ops: Optional client-defined tracing_map_ops instance
   * @private_data: Client data associated with the map
   *
   * Creates and sets up a map to contain 2 ** map_bits number of
   * elements (internally maintained as 'max_elts' in struct
   * tracing_map).  Before using, map fields should be added to the map
   * with tracing_map_add_sum_field() and tracing_map_add_key_field().
   * tracing_map_init() should then be called to allocate the array of
   * tracing_map_elts, in order to avoid allocating anything in the map
   * insertion path.  The user-specified map size reflects the maximum
   * number of elements that can be contained in the table requested by
   * the user - internally we double that in order to keep the table
   * sparse and keep collisions manageable.
   *
   * A tracing_map is a special-purpose map designed to aggregate or
   * 'sum' one or more values associated with a specific object of type
   * tracing_map_elt, which is attached by the map to a given key.
   *
   * tracing_map_create() sets up the map itself, and provides
   * operations for inserting tracing_map_elts, but doesn't allocate the
   * tracing_map_elts themselves, or provide a means for describing the
   * keys or sums associated with the tracing_map_elts.  All
   * tracing_map_elts for a given map have the same set of sums and
   * keys, which are defined by the client using the functions
   * tracing_map_add_key_field() and tracing_map_add_sum_field().  Once
   * the fields are defined, the pool of elements allocated for the map
   * can be created, which occurs when the client code calls
   * tracing_map_init().
   *
   * When tracing_map_init() returns, tracing_map_elt elements can be
   * inserted into the map using tracing_map_insert().  When called,
   * tracing_map_insert() grabs a free tracing_map_elt from the pool, or
   * finds an existing match in the map and in either case returns it.
   * The client can then use tracing_map_update_sum() and
   * tracing_map_read_sum() to update or read a given sum field for the
   * tracing_map_elt.
   *
   * The client can at any point retrieve and traverse the current set
   * of inserted tracing_map_elts in a tracing_map, via
   * tracing_map_sort_entries().  Sorting can be done on any field,
   * including keys.
   *
   * See tracing_map.h for a description of tracing_map_ops.
   *
   * Return: the tracing_map pointer if successful, ERR_PTR if not.
   */
  struct tracing_map *tracing_map_create(unsigned int map_bits,
  				       unsigned int key_size,
  				       const struct tracing_map_ops *ops,
  				       void *private_data)
  {
  	struct tracing_map *map;
  	unsigned int i;
  
  	if (map_bits < TRACING_MAP_BITS_MIN ||
  	    map_bits > TRACING_MAP_BITS_MAX)
  		return ERR_PTR(-EINVAL);
  
  	map = kzalloc(sizeof(*map), GFP_KERNEL);
  	if (!map)
  		return ERR_PTR(-ENOMEM);
  
  	map->map_bits = map_bits;
  	map->max_elts = (1 << map_bits);
  	atomic_set(&map->next_elt, -1);
  
  	map->map_size = (1 << (map_bits + 1));
  	map->ops = ops;
  
  	map->private_data = private_data;
  
  	map->map = tracing_map_array_alloc(map->map_size,
  					   sizeof(struct tracing_map_entry));
  	if (!map->map)
  		goto free;
  
  	map->key_size = key_size;
  	for (i = 0; i < TRACING_MAP_KEYS_MAX; i++)
  		map->key_idx[i] = -1;
   out:
  	return map;
   free:
  	tracing_map_destroy(map);
  	map = ERR_PTR(-ENOMEM);
  
  	goto out;
  }
  
  /**
   * tracing_map_init - Allocate and clear a map's tracing_map_elts
   * @map: The tracing_map to initialize
   *
   * Allocates a clears a pool of tracing_map_elts equal to the
   * user-specified size of 2 ** map_bits (internally maintained as
   * 'max_elts' in struct tracing_map).  Before using, the map fields
   * should be added to the map with tracing_map_add_sum_field() and
   * tracing_map_add_key_field().  tracing_map_init() should then be
   * called to allocate the array of tracing_map_elts, in order to avoid
   * allocating anything in the map insertion path.  The user-specified
   * map size reflects the max number of elements requested by the user
   * - internally we double that in order to keep the table sparse and
   * keep collisions manageable.
   *
   * See tracing_map.h for a description of tracing_map_ops.
   *
   * Return: the tracing_map pointer if successful, ERR_PTR if not.
   */
  int tracing_map_init(struct tracing_map *map)
  {
  	int err;
  
  	if (map->n_fields < 2)
  		return -EINVAL; /* need at least 1 key and 1 val */
  
  	err = tracing_map_alloc_elts(map);
  	if (err)
  		return err;
  
  	tracing_map_clear(map);
  
  	return err;
  }
  
  static int cmp_entries_dup(const struct tracing_map_sort_entry **a,
  			   const struct tracing_map_sort_entry **b)
  {
  	int ret = 0;
  
  	if (memcmp((*a)->key, (*b)->key, (*a)->elt->map->key_size))
  		ret = 1;
  
  	return ret;
  }
  
  static int cmp_entries_sum(const struct tracing_map_sort_entry **a,
  			   const struct tracing_map_sort_entry **b)
  {
  	const struct tracing_map_elt *elt_a, *elt_b;
  	struct tracing_map_sort_key *sort_key;
  	struct tracing_map_field *field;
  	tracing_map_cmp_fn_t cmp_fn;
  	void *val_a, *val_b;
  	int ret = 0;
  
  	elt_a = (*a)->elt;
  	elt_b = (*b)->elt;
  
  	sort_key = &elt_a->map->sort_key;
  
  	field = &elt_a->fields[sort_key->field_idx];
  	cmp_fn = field->cmp_fn;
  
  	val_a = &elt_a->fields[sort_key->field_idx].sum;
  	val_b = &elt_b->fields[sort_key->field_idx].sum;
  
  	ret = cmp_fn(val_a, val_b);
  	if (sort_key->descending)
  		ret = -ret;
  
  	return ret;
  }
  
  static int cmp_entries_key(const struct tracing_map_sort_entry **a,
  			   const struct tracing_map_sort_entry **b)
  {
  	const struct tracing_map_elt *elt_a, *elt_b;
  	struct tracing_map_sort_key *sort_key;
  	struct tracing_map_field *field;
  	tracing_map_cmp_fn_t cmp_fn;
  	void *val_a, *val_b;
  	int ret = 0;
  
  	elt_a = (*a)->elt;
  	elt_b = (*b)->elt;
  
  	sort_key = &elt_a->map->sort_key;
  
  	field = &elt_a->fields[sort_key->field_idx];
  
  	cmp_fn = field->cmp_fn;
  
  	val_a = elt_a->key + field->offset;
  	val_b = elt_b->key + field->offset;
  
  	ret = cmp_fn(val_a, val_b);
  	if (sort_key->descending)
  		ret = -ret;
  
  	return ret;
  }
  
  static void destroy_sort_entry(struct tracing_map_sort_entry *entry)
  {
  	if (!entry)
  		return;
  
  	if (entry->elt_copied)
  		tracing_map_elt_free(entry->elt);
  
  	kfree(entry);
  }
  
  /**
   * tracing_map_destroy_sort_entries - Destroy an array of sort entries
   * @entries: The entries to destroy
   * @n_entries: The number of entries in the array
   *
   * Destroy the elements returned by a tracing_map_sort_entries() call.
   */
  void tracing_map_destroy_sort_entries(struct tracing_map_sort_entry **entries,
  				      unsigned int n_entries)
  {
  	unsigned int i;
  
  	for (i = 0; i < n_entries; i++)
  		destroy_sort_entry(entries[i]);
  
  	vfree(entries);
  }
  
  static struct tracing_map_sort_entry *
  create_sort_entry(void *key, struct tracing_map_elt *elt)
  {
  	struct tracing_map_sort_entry *sort_entry;
  
  	sort_entry = kzalloc(sizeof(*sort_entry), GFP_KERNEL);
  	if (!sort_entry)
  		return NULL;
  
  	sort_entry->key = key;
  	sort_entry->elt = elt;
  
  	return sort_entry;
  }
  
  static struct tracing_map_elt *copy_elt(struct tracing_map_elt *elt)
  {
  	struct tracing_map_elt *dup_elt;
  	unsigned int i;
  
  	dup_elt = tracing_map_elt_alloc(elt->map);
  	if (IS_ERR(dup_elt))
  		return NULL;
  
  	if (elt->map->ops && elt->map->ops->elt_copy)
  		elt->map->ops->elt_copy(dup_elt, elt);
  
  	dup_elt->private_data = elt->private_data;
  	memcpy(dup_elt->key, elt->key, elt->map->key_size);
  
  	for (i = 0; i < elt->map->n_fields; i++) {
  		atomic64_set(&dup_elt->fields[i].sum,
  			     atomic64_read(&elt->fields[i].sum));
  		dup_elt->fields[i].cmp_fn = elt->fields[i].cmp_fn;
  	}
  
  	return dup_elt;
  }
  
  static int merge_dup(struct tracing_map_sort_entry **sort_entries,
  		     unsigned int target, unsigned int dup)
  {
  	struct tracing_map_elt *target_elt, *elt;
  	bool first_dup = (target - dup) == 1;
  	int i;
  
  	if (first_dup) {
  		elt = sort_entries[target]->elt;
  		target_elt = copy_elt(elt);
  		if (!target_elt)
  			return -ENOMEM;
  		sort_entries[target]->elt = target_elt;
  		sort_entries[target]->elt_copied = true;
  	} else
  		target_elt = sort_entries[target]->elt;
  
  	elt = sort_entries[dup]->elt;
  
  	for (i = 0; i < elt->map->n_fields; i++)
  		atomic64_add(atomic64_read(&elt->fields[i].sum),
  			     &target_elt->fields[i].sum);
  
  	sort_entries[dup]->dup = true;
  
  	return 0;
  }
  
  static int merge_dups(struct tracing_map_sort_entry **sort_entries,
  		      int n_entries, unsigned int key_size)
  {
  	unsigned int dups = 0, total_dups = 0;
  	int err, i, j;
  	void *key;
  
  	if (n_entries < 2)
  		return total_dups;
  
  	sort(sort_entries, n_entries, sizeof(struct tracing_map_sort_entry *),
  	     (int (*)(const void *, const void *))cmp_entries_dup, NULL);
  
  	key = sort_entries[0]->key;
  	for (i = 1; i < n_entries; i++) {
  		if (!memcmp(sort_entries[i]->key, key, key_size)) {
  			dups++; total_dups++;
  			err = merge_dup(sort_entries, i - dups, i);
  			if (err)
  				return err;
  			continue;
  		}
  		key = sort_entries[i]->key;
  		dups = 0;
  	}
  
  	if (!total_dups)
  		return total_dups;
  
  	for (i = 0, j = 0; i < n_entries; i++) {
  		if (!sort_entries[i]->dup) {
  			sort_entries[j] = sort_entries[i];
  			if (j++ != i)
  				sort_entries[i] = NULL;
  		} else {
  			destroy_sort_entry(sort_entries[i]);
  			sort_entries[i] = NULL;
  		}
  	}
  
  	return total_dups;
  }
  
  static bool is_key(struct tracing_map *map, unsigned int field_idx)
  {
  	unsigned int i;
  
  	for (i = 0; i < map->n_keys; i++)
  		if (map->key_idx[i] == field_idx)
  			return true;
  	return false;
  }
  
  static void sort_secondary(struct tracing_map *map,
  			   const struct tracing_map_sort_entry **entries,
  			   unsigned int n_entries,
  			   struct tracing_map_sort_key *primary_key,
  			   struct tracing_map_sort_key *secondary_key)
  {
  	int (*primary_fn)(const struct tracing_map_sort_entry **,
  			  const struct tracing_map_sort_entry **);
  	int (*secondary_fn)(const struct tracing_map_sort_entry **,
  			    const struct tracing_map_sort_entry **);
  	unsigned i, start = 0, n_sub = 1;
  
  	if (is_key(map, primary_key->field_idx))
  		primary_fn = cmp_entries_key;
  	else
  		primary_fn = cmp_entries_sum;
  
  	if (is_key(map, secondary_key->field_idx))
  		secondary_fn = cmp_entries_key;
  	else
  		secondary_fn = cmp_entries_sum;
  
  	for (i = 0; i < n_entries - 1; i++) {
  		const struct tracing_map_sort_entry **a = &entries[i];
  		const struct tracing_map_sort_entry **b = &entries[i + 1];
  
  		if (primary_fn(a, b) == 0) {
  			n_sub++;
  			if (i < n_entries - 2)
  				continue;
  		}
  
  		if (n_sub < 2) {
  			start = i + 1;
  			n_sub = 1;
  			continue;
  		}
  
  		set_sort_key(map, secondary_key);
  		sort(&entries[start], n_sub,
  		     sizeof(struct tracing_map_sort_entry *),
  		     (int (*)(const void *, const void *))secondary_fn, NULL);
  		set_sort_key(map, primary_key);
  
  		start = i + 1;
  		n_sub = 1;
  	}
  }
  
  /**
   * tracing_map_sort_entries - Sort the current set of tracing_map_elts in a map
   * @map: The tracing_map
   * @sort_key: The sort key to use for sorting
   * @sort_entries: outval: pointer to allocated and sorted array of entries
   *
   * tracing_map_sort_entries() sorts the current set of entries in the
   * map and returns the list of tracing_map_sort_entries containing
   * them to the client in the sort_entries param.  The client can
   * access the struct tracing_map_elt element of interest directly as
   * the 'elt' field of a returned struct tracing_map_sort_entry object.
   *
   * The sort_key has only two fields: idx and descending.  'idx' refers
   * to the index of the field added via tracing_map_add_sum_field() or
   * tracing_map_add_key_field() when the tracing_map was initialized.
   * 'descending' is a flag that if set reverses the sort order, which
   * by default is ascending.
   *
   * The client should not hold on to the returned array but should use
   * it and call tracing_map_destroy_sort_entries() when done.
   *
   * Return: the number of sort_entries in the struct tracing_map_sort_entry
   * array, negative on error
   */
  int tracing_map_sort_entries(struct tracing_map *map,
  			     struct tracing_map_sort_key *sort_keys,
  			     unsigned int n_sort_keys,
  			     struct tracing_map_sort_entry ***sort_entries)
  {
  	int (*cmp_entries_fn)(const struct tracing_map_sort_entry **,
  			      const struct tracing_map_sort_entry **);
  	struct tracing_map_sort_entry *sort_entry, **entries;
  	int i, n_entries, ret;
  
  	entries = vmalloc(map->max_elts * sizeof(sort_entry));
  	if (!entries)
  		return -ENOMEM;
  
  	for (i = 0, n_entries = 0; i < map->map_size; i++) {
  		struct tracing_map_entry *entry;
  
  		entry = TRACING_MAP_ENTRY(map->map, i);
  
  		if (!entry->key || !entry->val)
  			continue;
  
  		entries[n_entries] = create_sort_entry(entry->val->key,
  						       entry->val);
  		if (!entries[n_entries++]) {
  			ret = -ENOMEM;
  			goto free;
  		}
  	}
  
  	if (n_entries == 0) {
  		ret = 0;
  		goto free;
  	}
  
  	if (n_entries == 1) {
  		*sort_entries = entries;
  		return 1;
  	}
  
  	ret = merge_dups(entries, n_entries, map->key_size);
  	if (ret < 0)
  		goto free;
  	n_entries -= ret;
  
  	if (is_key(map, sort_keys[0].field_idx))
  		cmp_entries_fn = cmp_entries_key;
  	else
  		cmp_entries_fn = cmp_entries_sum;
  
  	set_sort_key(map, &sort_keys[0]);
  
  	sort(entries, n_entries, sizeof(struct tracing_map_sort_entry *),
  	     (int (*)(const void *, const void *))cmp_entries_fn, NULL);
  
  	if (n_sort_keys > 1)
  		sort_secondary(map,
  			       (const struct tracing_map_sort_entry **)entries,
  			       n_entries,
  			       &sort_keys[0],
  			       &sort_keys[1]);
  
  	*sort_entries = entries;
  
  	return n_entries;
   free:
  	tracing_map_destroy_sort_entries(entries, n_entries);
  
  	return ret;
  }
  