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("btrfs_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        INIT_LIST_HEAD(&tree->modified_extents);
  39        rwlock_init(&tree->lock);
  40}
  41
  42/**
  43 * alloc_extent_map - allocate new extent map structure
  44 *
  45 * Allocate a new extent_map structure.  The new structure is
  46 * returned with a reference count of one and needs to be
  47 * freed using free_extent_map()
  48 */
  49struct extent_map *alloc_extent_map(void)
  50{
  51        struct extent_map *em;
  52        em = kmem_cache_alloc(extent_map_cache, GFP_NOFS);
  53        if (!em)
  54                return NULL;
  55        em->in_tree = 0;
  56        em->flags = 0;
  57        em->compress_type = BTRFS_COMPRESS_NONE;
  58        em->generation = 0;
  59        atomic_set(&em->refs, 1);
  60        INIT_LIST_HEAD(&em->list);
  61        return em;
  62}
  63
  64/**
  65 * free_extent_map - drop reference count of an extent_map
  66 * @em:         extent map beeing releasead
  67 *
  68 * Drops the reference out on @em by one and free the structure
  69 * if the reference count hits zero.
  70 */
  71void free_extent_map(struct extent_map *em)
  72{
  73        if (!em)
  74                return;
  75        WARN_ON(atomic_read(&em->refs) == 0);
  76        if (atomic_dec_and_test(&em->refs)) {
  77                WARN_ON(em->in_tree);
  78                WARN_ON(!list_empty(&em->list));
  79                kmem_cache_free(extent_map_cache, em);
  80        }
  81}
  82
  83static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
  84                                   struct rb_node *node)
  85{
  86        struct rb_node **p = &root->rb_node;
  87        struct rb_node *parent = NULL;
  88        struct extent_map *entry;
  89
  90        while (*p) {
  91                parent = *p;
  92                entry = rb_entry(parent, struct extent_map, rb_node);
  93
  94                WARN_ON(!entry->in_tree);
  95
  96                if (offset < entry->start)
  97                        p = &(*p)->rb_left;
  98                else if (offset >= extent_map_end(entry))
  99                        p = &(*p)->rb_right;
 100                else
 101                        return parent;
 102        }
 103
 104        entry = rb_entry(node, struct extent_map, rb_node);
 105        entry->in_tree = 1;
 106        rb_link_node(node, parent, p);
 107        rb_insert_color(node, root);
 108        return NULL;
 109}
 110
 111/*
 112 * search through the tree for an extent_map with a given offset.  If
 113 * it can't be found, try to find some neighboring extents
 114 */
 115static struct rb_node *__tree_search(struct rb_root *root, u64 offset,
 116                                     struct rb_node **prev_ret,
 117                                     struct rb_node **next_ret)
 118{
 119        struct rb_node *n = root->rb_node;
 120        struct rb_node *prev = NULL;
 121        struct rb_node *orig_prev = NULL;
 122        struct extent_map *entry;
 123        struct extent_map *prev_entry = NULL;
 124
 125        while (n) {
 126                entry = rb_entry(n, struct extent_map, rb_node);
 127                prev = n;
 128                prev_entry = entry;
 129
 130                WARN_ON(!entry->in_tree);
 131
 132                if (offset < entry->start)
 133                        n = n->rb_left;
 134                else if (offset >= extent_map_end(entry))
 135                        n = n->rb_right;
 136                else
 137                        return n;
 138        }
 139
 140        if (prev_ret) {
 141                orig_prev = prev;
 142                while (prev && offset >= extent_map_end(prev_entry)) {
 143                        prev = rb_next(prev);
 144                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
 145                }
 146                *prev_ret = prev;
 147                prev = orig_prev;
 148        }
 149
 150        if (next_ret) {
 151                prev_entry = rb_entry(prev, struct extent_map, rb_node);
 152                while (prev && offset < prev_entry->start) {
 153                        prev = rb_prev(prev);
 154                        prev_entry = rb_entry(prev, struct extent_map, rb_node);
 155                }
 156                *next_ret = prev;
 157        }
 158        return NULL;
 159}
 160
 161/* check to see if two extent_map structs are adjacent and safe to merge */
 162static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 163{
 164        if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
 165                return 0;
 166
 167        /*
 168         * don't merge compressed extents, we need to know their
 169         * actual size
 170         */
 171        if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
 172                return 0;
 173
 174        if (extent_map_end(prev) == next->start &&
 175            prev->flags == next->flags &&
 176            prev->bdev == next->bdev &&
 177            ((next->block_start == EXTENT_MAP_HOLE &&
 178              prev->block_start == EXTENT_MAP_HOLE) ||
 179             (next->block_start == EXTENT_MAP_INLINE &&
 180              prev->block_start == EXTENT_MAP_INLINE) ||
 181             (next->block_start == EXTENT_MAP_DELALLOC &&
 182              prev->block_start == EXTENT_MAP_DELALLOC) ||
 183             (next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
 184              next->block_start == extent_map_block_end(prev)))) {
 185                return 1;
 186        }
 187        return 0;
 188}
 189
 190static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
 191{
 192        struct extent_map *merge = NULL;
 193        struct rb_node *rb;
 194
 195        if (em->start != 0) {
 196                rb = rb_prev(&em->rb_node);
 197                if (rb)
 198                        merge = rb_entry(rb, struct extent_map, rb_node);
 199                if (rb && mergable_maps(merge, em)) {
 200                        em->start = merge->start;
 201                        em->len += merge->len;
 202                        em->block_len += merge->block_len;
 203                        em->block_start = merge->block_start;
 204                        merge->in_tree = 0;
 205                        if (merge->generation > em->generation) {
 206                                em->mod_start = em->start;
 207                                em->mod_len = em->len;
 208                                em->generation = merge->generation;
 209                                list_move(&em->list, &tree->modified_extents);
 210                        }
 211
 212                        list_del_init(&merge->list);
 213                        rb_erase(&merge->rb_node, &tree->map);
 214                        free_extent_map(merge);
 215                }
 216        }
 217
 218        rb = rb_next(&em->rb_node);
 219        if (rb)
 220                merge = rb_entry(rb, struct extent_map, rb_node);
 221        if (rb && mergable_maps(em, merge)) {
 222                em->len += merge->len;
 223                em->block_len += merge->len;
 224                rb_erase(&merge->rb_node, &tree->map);
 225                merge->in_tree = 0;
 226                if (merge->generation > em->generation) {
 227                        em->mod_len = em->len;
 228                        em->generation = merge->generation;
 229                        list_move(&em->list, &tree->modified_extents);
 230                }
 231                list_del_init(&merge->list);
 232                free_extent_map(merge);
 233        }
 234}
 235
 236/**
 237 * unpint_extent_cache - unpin an extent from the cache
 238 * @tree:       tree to unpin the extent in
 239 * @start:      logical offset in the file
 240 * @len:        length of the extent
 241 * @gen:        generation that this extent has been modified in
 242 * @prealloc:   if this is set we need to clear the prealloc flag
 243 *
 244 * Called after an extent has been written to disk properly.  Set the generation
 245 * to the generation that actually added the file item to the inode so we know
 246 * we need to sync this extent when we call fsync().
 247 */
 248int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len,
 249                       u64 gen)
 250{
 251        int ret = 0;
 252        struct extent_map *em;
 253        bool prealloc = false;
 254
 255        write_lock(&tree->lock);
 256        em = lookup_extent_mapping(tree, start, len);
 257
 258        WARN_ON(!em || em->start != start);
 259
 260        if (!em)
 261                goto out;
 262
 263        list_move(&em->list, &tree->modified_extents);
 264        em->generation = gen;
 265        clear_bit(EXTENT_FLAG_PINNED, &em->flags);
 266        em->mod_start = em->start;
 267        em->mod_len = em->len;
 268
 269        if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
 270                prealloc = true;
 271                clear_bit(EXTENT_FLAG_PREALLOC, &em->flags);
 272        }
 273
 274        try_merge_map(tree, em);
 275
 276        if (prealloc) {
 277                em->mod_start = em->start;
 278                em->mod_len = em->len;
 279        }
 280
 281        free_extent_map(em);
 282out:
 283        write_unlock(&tree->lock);
 284        return ret;
 285
 286}
 287
 288/**
 289 * add_extent_mapping - add new extent map to the extent tree
 290 * @tree:       tree to insert new map in
 291 * @em:         map to insert
 292 *
 293 * Insert @em into @tree or perform a simple forward/backward merge with
 294 * existing mappings.  The extent_map struct passed in will be inserted
 295 * into the tree directly, with an additional reference taken, or a
 296 * reference dropped if the merge attempt was successful.
 297 */
 298int add_extent_mapping(struct extent_map_tree *tree,
 299                       struct extent_map *em)
 300{
 301        int ret = 0;
 302        struct rb_node *rb;
 303        struct extent_map *exist;
 304
 305        exist = lookup_extent_mapping(tree, em->start, em->len);
 306        if (exist) {
 307                free_extent_map(exist);
 308                ret = -EEXIST;
 309                goto out;
 310        }
 311        rb = tree_insert(&tree->map, em->start, &em->rb_node);
 312        if (rb) {
 313                ret = -EEXIST;
 314                goto out;
 315        }
 316        atomic_inc(&em->refs);
 317
 318        em->mod_start = em->start;
 319        em->mod_len = em->len;
 320
 321        try_merge_map(tree, em);
 322out:
 323        return ret;
 324}
 325
 326/* simple helper to do math around the end of an extent, handling wrap */
 327static u64 range_end(u64 start, u64 len)
 328{
 329        if (start + len < start)
 330                return (u64)-1;
 331        return start + len;
 332}
 333
 334struct extent_map *__lookup_extent_mapping(struct extent_map_tree *tree,
 335                                           u64 start, u64 len, int strict)
 336{
 337        struct extent_map *em;
 338        struct rb_node *rb_node;
 339        struct rb_node *prev = NULL;
 340        struct rb_node *next = NULL;
 341        u64 end = range_end(start, len);
 342
 343        rb_node = __tree_search(&tree->map, start, &prev, &next);
 344        if (!rb_node) {
 345                if (prev)
 346                        rb_node = prev;
 347                else if (next)
 348                        rb_node = next;
 349                else
 350                        return NULL;
 351        }
 352
 353        em = rb_entry(rb_node, struct extent_map, rb_node);
 354
 355        if (strict && !(end > em->start && start < extent_map_end(em)))
 356                return NULL;
 357
 358        atomic_inc(&em->refs);
 359        return em;
 360}
 361
 362/**
 363 * lookup_extent_mapping - lookup extent_map
 364 * @tree:       tree to lookup in
 365 * @start:      byte offset to start the search
 366 * @len:        length of the lookup range
 367 *
 368 * Find and return the first extent_map struct in @tree that intersects the
 369 * [start, len] range.  There may be additional objects in the tree that
 370 * intersect, so check the object returned carefully to make sure that no
 371 * additional lookups are needed.
 372 */
 373struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
 374                                         u64 start, u64 len)
 375{
 376        return __lookup_extent_mapping(tree, start, len, 1);
 377}
 378
 379/**
 380 * search_extent_mapping - find a nearby extent map
 381 * @tree:       tree to lookup in
 382 * @start:      byte offset to start the search
 383 * @len:        length of the lookup range
 384 *
 385 * Find and return the first extent_map struct in @tree that intersects the
 386 * [start, len] range.
 387 *
 388 * If one can't be found, any nearby extent may be returned
 389 */
 390struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
 391                                         u64 start, u64 len)
 392{
 393        return __lookup_extent_mapping(tree, start, len, 0);
 394}
 395
 396/**
 397 * remove_extent_mapping - removes an extent_map from the extent tree
 398 * @tree:       extent tree to remove from
 399 * @em:         extent map beeing removed
 400 *
 401 * Removes @em from @tree.  No reference counts are dropped, and no checks
 402 * are done to see if the range is in use
 403 */
 404int remove_extent_mapping(struct extent_map_tree *tree, struct extent_map *em)
 405{
 406        int ret = 0;
 407
 408        WARN_ON(test_bit(EXTENT_FLAG_PINNED, &em->flags));
 409        rb_erase(&em->rb_node, &tree->map);
 410        if (!test_bit(EXTENT_FLAG_LOGGING, &em->flags))
 411                list_del_init(&em->list);
 412        em->in_tree = 0;
 413        return ret;
 414}
 415
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