linux/fs/btrfs/extent_map.c
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   1#include <linux/err.h>
   2#include <linux/slab.h>
   3#include <linux/module.h>
   4#include <linux/spinlock.h>
   5#include <linux/hardirq.h>
   6#include "ctree.h"
   7#include "extent_map.h"
   8
   9
  10static struct kmem_cache *extent_map_cache;
  11
  12int __init extent_map_init(void)
  13{
  14        extent_map_cache = kmem_cache_create("extent_map",
  15                        sizeof(struct extent_map), 0,
  16                        SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
  17        if (!extent_map_cache)
  18                return -ENOMEM;
  19        return 0;
  20}
  21
  22void extent_map_exit(void)
  23{
  24        if (extent_map_cache)
  25                kmem_cache_destroy(extent_map_cache);
  26}
  27
  28/**
  29 * extent_map_tree_init - initialize extent map tree
  30 * @tree:               tree to initialize
  31 *
  32 * Initialize the extent tree @tree.  Should be called for each new inode
  33 * or other user of the extent_map interface.
  34 */
  35void extent_map_tree_init(struct extent_map_tree *tree)
  36{
  37        tree->map = RB_ROOT;
  38        rwlock_init(&tree->lock);
  39}
  40
  41/**
  42 * alloc_extent_map - allocate new extent map structure
  43 *
  44 * Allocate a new extent_map structure.  The new structure is
  45 * returned with a reference count of one and needs to be
  46 * freed using free_extent_map()
  47 */
  48struct extent_map *alloc_extent_map(void)
  49{
  50        struct extent_map *em;
  51        em = kmem_cache_alloc(extent_map_cache, GFP_NOFS);
  52        if (!em)
  53                return NULL;
  54        em->in_tree = 0;
  55        em->flags = 0;
  56        em->compress_type = BTRFS_COMPRESS_NONE;
  57        atomic_set(&em->refs, 1);
  58        return em;
  59}
  60
  61/**
  62 * free_extent_map - drop reference count of an extent_map
  63 * @em:         extent map beeing releasead
  64 *
  65 * Drops the reference out on @em by one and free the structure
  66 * if the reference count hits zero.
  67 */
  68void free_extent_map(struct extent_map *em)
  69{
  70        if (!em)
  71                return;
  72        WARN_ON(atomic_read(&em->refs) == 0);
  73        if (atomic_dec_and_test(&em->refs)) {
  74                WARN_ON(em->in_tree);
  75                kmem_cache_free(extent_map_cache, em);
  76        }
  77}
  78
  79static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
  80                                   struct rb_node *node)
  81{
  82        struct rb_node **p = &root->rb_node;
  83        struct rb_node *parent = NULL;
  84        struct extent_map *entry;
  85
  86        while (*p) {
  87                parent = *p;
  88                entry = rb_entry(parent, struct extent_map, rb_node);
  89
  90                WARN_ON(!entry->in_tree);
  91
  92                if (offset < entry->start)
  93                        p = &(*p)->rb_left;
  94                else if (offset >= extent_map_end(entry))
  95                        p = &(*p)->rb_right;
  96                else
  97                        return parent;
  98        }
  99
 100        entry = rb_entry(node, struct extent_map, rb_node);
 101        entry->in_tree = 1;
 102        rb_link_node(node, parent, p);
 103        rb_insert_color(node, root);
 104        return NULL;
 105}
 106
 107/*
 108 * search through the tree for an extent_map with a given offset.  If
 109 * it can't be found, try to find some neighboring extents
 110 */
 111static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 112                                     struct rb_node **prev_ret,
 113                                     struct rb_node **next_ret)
 114{
 115        struct rb_node *n = root->rb_node;
 116        struct rb_node *prev = NULL;
 117        struct rb_node *orig_prev = NULL;
 118        struct extent_map *entry;
 119        struct extent_map *prev_entry = NULL;
 120
 121        while (n) {
 122                entry = rb_entry(n, struct extent_map, rb_node);
 123                prev = n;
 124                prev_entry = entry;
 125
 126                WARN_ON(!entry->in_tree);
 127
 128                if (offset < entry->start)
 129                        n = n->rb_left;
 130                else if (offset >= extent_map_end(entry))
 131                        n = n->rb_right;
 132                else
 133                        return n;
 134        }
 135
 136        if (prev_ret) {
 137                orig_prev = prev;
 138                while (prev && offset >= extent_map_end(prev_entry)) {
 139                        prev = rb_next(prev);
 140                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
 141                }
 142                *prev_ret = prev;
 143                prev = orig_prev;
 144        }
 145
 146        if (next_ret) {
 147                prev_entry = rb_entry(prev, struct extent_map, rb_node);
 148                while (prev && offset < prev_entry->start) {
 149                        prev = rb_prev(prev);
 150                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
 151                }
 152                *next_ret = prev;
 153        }
 154        return NULL;
 155}
 156
 157/* check to see if two extent_map structs are adjacent and safe to merge */
 158static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 159{
 160        if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
 161                return 0;
 162
 163        /*
 164         * don't merge compressed extents, we need to know their
 165         * actual size
 166         */
 167        if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
 168                return 0;
 169
 170        if (extent_map_end(prev) == next->start &&
 171            prev->flags == next->flags &&
 172            prev->bdev == next->bdev &&
 173            ((next->block_start == EXTENT_MAP_HOLE &&
 174              prev->block_start == EXTENT_MAP_HOLE) ||
 175             (next->block_start == EXTENT_MAP_INLINE &&
 176              prev->block_start == EXTENT_MAP_INLINE) ||
 177             (next->block_start == EXTENT_MAP_DELALLOC &&
 178              prev->block_start == EXTENT_MAP_DELALLOC) ||
 179             (next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
 180              next->block_start == extent_map_block_end(prev)))) {
 181                return 1;
 182        }
 183        return 0;
 184}
 185
 186static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
 187{
 188        struct extent_map *merge = NULL;
 189        struct rb_node *rb;
 190
 191        if (em->start != 0) {
 192                rb = rb_prev(&em->rb_node);
 193                if (rb)
 194                        merge = rb_entry(rb, struct extent_map, rb_node);
 195                if (rb && mergable_maps(merge, em)) {
 196                        em->start = merge->start;
 197                        em->len += merge->len;
 198                        em->block_len += merge->block_len;
 199                        em->block_start = merge->block_start;
 200                        merge->in_tree = 0;
 201                        rb_erase(&merge->rb_node, &tree->map);
 202                        free_extent_map(merge);
 203                }
 204        }
 205
 206        rb = rb_next(&em->rb_node);
 207        if (rb)
 208                merge = rb_entry(rb, struct extent_map, rb_node);
 209        if (rb && mergable_maps(em, merge)) {
 210                em->len += merge->len;
 211                em->block_len += merge->len;
 212                rb_erase(&merge->rb_node, &tree->map);
 213                merge->in_tree = 0;
 214                free_extent_map(merge);
 215        }
 216}
 217
 218int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len)
 219{
 220        int ret = 0;
 221        struct extent_map *em;
 222
 223        write_lock(&tree->lock);
 224        em = lookup_extent_mapping(tree, start, len);
 225
 226        WARN_ON(!em || em->start != start);
 227
 228        if (!em)
 229                goto out;
 230
 231        clear_bit(EXTENT_FLAG_PINNED, &em->flags);
 232
 233        try_merge_map(tree, em);
 234
 235        free_extent_map(em);
 236out:
 237        write_unlock(&tree->lock);
 238        return ret;
 239
 240}
 241
 242/**
 243 * add_extent_mapping - add new extent map to the extent tree
 244 * @tree:       tree to insert new map in
 245 * @em:         map to insert
 246 *
 247 * Insert @em into @tree or perform a simple forward/backward merge with
 248 * existing mappings.  The extent_map struct passed in will be inserted
 249 * into the tree directly, with an additional reference taken, or a
 250 * reference dropped if the merge attempt was successful.
 251 */
 252int add_extent_mapping(struct extent_map_tree *tree,
 253                       struct extent_map *em)
 254{
 255        int ret = 0;
 256        struct rb_node *rb;
 257        struct extent_map *exist;
 258
 259        exist = lookup_extent_mapping(tree, em->start, em->len);
 260        if (exist) {
 261                free_extent_map(exist);
 262                ret = -EEXIST;
 263                goto out;
 264        }
 265        rb = tree_insert(&tree->map, em->start, &em->rb_node);
 266        if (rb) {
 267                ret = -EEXIST;
 268                goto out;
 269        }
 270        atomic_inc(&em->refs);
 271
 272        try_merge_map(tree, em);
 273out:
 274        return ret;
 275}
 276
 277/* simple helper to do math around the end of an extent, handling wrap */
 278static u64 range_end(u64 start, u64 len)
 279{
 280        if (start + len < start)
 281                return (u64)-1;
 282        return start + len;
 283}
 284
 285struct extent_map *__lookup_extent_mapping(struct extent_map_tree *tree,
 286                                           u64 start, u64 len, int strict)
 287{
 288        struct extent_map *em;
 289        struct rb_node *rb_node;
 290        struct rb_node *prev = NULL;
 291        struct rb_node *next = NULL;
 292        u64 end = range_end(start, len);
 293
 294        rb_node = __tree_search(&tree->map, start, &prev, &next);
 295        if (!rb_node) {
 296                if (prev)
 297                        rb_node = prev;
 298                else if (next)
 299                        rb_node = next;
 300                else
 301                        return NULL;
 302        }
 303
 304        em = rb_entry(rb_node, struct extent_map, rb_node);
 305
 306        if (strict && !(end > em->start && start < extent_map_end(em)))
 307                return NULL;
 308
 309        atomic_inc(&em->refs);
 310        return em;
 311}
 312
 313/**
 314 * lookup_extent_mapping - lookup extent_map
 315 * @tree:       tree to lookup in
 316 * @start:      byte offset to start the search
 317 * @len:        length of the lookup range
 318 *
 319 * Find and return the first extent_map struct in @tree that intersects the
 320 * [start, len] range.  There may be additional objects in the tree that
 321 * intersect, so check the object returned carefully to make sure that no
 322 * additional lookups are needed.
 323 */
 324struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
 325                                         u64 start, u64 len)
 326{
 327        return __lookup_extent_mapping(tree, start, len, 1);
 328}
 329
 330/**
 331 * search_extent_mapping - find a nearby extent map
 332 * @tree:       tree to lookup in
 333 * @start:      byte offset to start the search
 334 * @len:        length of the lookup range
 335 *
 336 * Find and return the first extent_map struct in @tree that intersects the
 337 * [start, len] range.
 338 *
 339 * If one can't be found, any nearby extent may be returned
 340 */
 341struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
 342                                         u64 start, u64 len)
 343{
 344        return __lookup_extent_mapping(tree, start, len, 0);
 345}
 346
 347/**
 348 * remove_extent_mapping - removes an extent_map from the extent tree
 349 * @tree:       extent tree to remove from
 350 * @em:         extent map beeing removed
 351 *
 352 * Removes @em from @tree.  No reference counts are dropped, and no checks
 353 * are done to see if the range is in use
 354 */
 355int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
 356{
 357        int ret = 0;
 358
 359        WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
 360        rb_erase(&em->rb_node, &tree->map);
 361        em->in_tree = 0;
 362        return ret;
 363}
 364
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