fs/btrfs/extent_map.c

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