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 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _BCACHE_BTREE_H
 #define _BCACHE_BTREE_H
 
 /*
  * THE BTREE:
  *
  * At a high level, bcache's btree is relatively standard b+ tree. All keys and
  * pointers are in the leaves; interior nodes only have pointers to the child
  * nodes.
  *
  * In the interior nodes, a struct bkey always points to a child btree node, and
  * the key is the highest key in the child node - except that the highest key in
  * an interior node is always MAX_KEY. The size field refers to the size on disk
  * of the child node - this would allow us to have variable sized btree nodes
  * (handy for keeping the depth of the btree 1 by expanding just the root).
  *
  * Btree nodes are themselves log structured, but this is hidden fairly
  * thoroughly. Btree nodes on disk will in practice have extents that overlap
  * (because they were written at different times), but in memory we never have
  * overlapping extents - when we read in a btree node from disk, the first thing
  * we do is resort all the sets of keys with a mergesort, and in the same pass
  * we check for overlapping extents and adjust them appropriately.
  *
  * struct btree_op is a central interface to the btree code. It's used for
  * specifying read vs. write locking, and the embedded closure is used for
  * waiting on IO or reserve memory.
  *
  * BTREE CACHE:
  *
  * Btree nodes are cached in memory; traversing the btree might require reading
  * in btree nodes which is handled mostly transparently.
  *
  * bch_btree_node_get() looks up a btree node in the cache and reads it in from
  * disk if necessary. This function is almost never called directly though - the
  * btree() macro is used to get a btree node, call some function on it, and
  * unlock the node after the function returns.
  *
  * The root is special cased - it's taken out of the cache's lru (thus pinning
  * it in memory), so we can find the root of the btree by just dereferencing a
  * pointer instead of looking it up in the cache. This makes locking a bit
  * tricky, since the root pointer is protected by the lock in the btree node it
  * points to - the btree_root() macro handles this.
  *
  * In various places we must be able to allocate memory for multiple btree nodes
  * in order to make forward progress. To do this we use the btree cache itself
  * as a reserve; if __get_free_pages() fails, we'll find a node in the btree
  * cache we can reuse. We can't allow more than one thread to be doing this at a
  * time, so there's a lock, implemented by a pointer to the btree_op closure -
  * this allows the btree_root() macro to implicitly release this lock.
  *
  * BTREE IO:
  *
  * Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
  * this.
  *
  * For writing, we have two btree_write structs embeddded in struct btree - one
  * write in flight, and one being set up, and we toggle between them.
  *
  * Writing is done with a single function -  bch_btree_write() really serves two
  * different purposes and should be broken up into two different functions. When
  * passing now = false, it merely indicates that the node is now dirty - calling
  * it ensures that the dirty keys will be written at some point in the future.
  *
  * When passing now = true, bch_btree_write() causes a write to happen
  * "immediately" (if there was already a write in flight, it'll cause the write
  * to happen as soon as the previous write completes). It returns immediately
  * though - but it takes a refcount on the closure in struct btree_op you passed
  * to it, so a closure_sync() later can be used to wait for the write to
  * complete.
  *
  * This is handy because btree_split() and garbage collection can issue writes
  * in parallel, reducing the amount of time they have to hold write locks.
  *
  * LOCKING:
  *
  * When traversing the btree, we may need write locks starting at some level -
  * inserting a key into the btree will typically only require a write lock on
  * the leaf node.
  *
  * This is specified with the lock field in struct btree_op; lock = 0 means we
  * take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
  * checks this field and returns the node with the appropriate lock held.
  *
  * If, after traversing the btree, the insertion code discovers it has to split
  * then it must restart from the root and take new locks - to do this it changes
  * the lock field and returns -EINTR, which causes the btree_root() macro to
  * loop.
  *
  * Handling cache misses require a different mechanism for upgrading to a write
  * lock. We do cache lookups with only a read lock held, but if we get a cache
  * miss and we wish to insert this data into the cache, we have to insert a
  * placeholder key to detect races - otherwise, we could race with a write and
  * overwrite the data that was just written to the cache with stale data from
  * the backing device.
  *
  * For this we use a sequence number that write locks and unlocks increment - to
  * insert the check key it unlocks the btree node and then takes a write lock,
  * and fails if the sequence number doesn't match.
  */
 
 #include "bset.h"
 #include "debug.h"
 
 struct btree_write {
     atomic_t        *journal;
 
     /* If btree_split() frees a btree node, it writes a new pointer to that
      * btree node indicating it was freed; it takes a refcount on
      * c->prio_blocked because we can't write the gens until the new
      * pointer is on disk. This allows btree_write_endio() to release the
      * refcount that btree_split() took.
      */
     int         prio_blocked;
 };
 
 struct btree {
     /* Hottest entries first */
     struct hlist_node   hash;
 
     /* Key/pointer for this btree node */
     BKEY_PADDED(key);
 
     unsigned long       seq;
     struct rw_semaphore lock;
     struct cache_set    *c;
     struct btree        *parent;
 
     struct mutex        write_lock;
 
     unsigned long       flags;
     uint16_t        written;    /* would be nice to kill */
     uint8_t         level;
 
     struct btree_keys   keys;
 
     /* For outstanding btree writes, used as a lock - protects write_idx */
     struct closure      io;
     struct semaphore    io_mutex;
 
     struct list_head    list;
     struct delayed_work work;
 
     struct btree_write  writes[2];
     struct bio      *bio;
 };
 
 
 
 
 #define BTREE_FLAG(flag)                        \
 static inline bool btree_node_ ## flag(struct btree *b)         \
 {   return test_bit(BTREE_NODE_ ## flag, &b->flags); }      \
                                     \
 static inline void set_btree_node_ ## flag(struct btree *b)     \
 {   set_bit(BTREE_NODE_ ## flag, &b->flags); }
 
 enum btree_flags {
     BTREE_NODE_io_error,
     BTREE_NODE_dirty,
     BTREE_NODE_write_idx,
     BTREE_NODE_journal_flush,
 };
 
 BTREE_FLAG(io_error);
 BTREE_FLAG(dirty);
 BTREE_FLAG(write_idx);
 BTREE_FLAG(journal_flush);
 
 static inline struct btree_write *btree_current_write(struct btree *b)
 {
     return b->writes + btree_node_write_idx(b);
 }
 
 static inline struct btree_write *btree_prev_write(struct btree *b)
 {
     return b->writes + (btree_node_write_idx(b) ^ 1);
 }
 
 static inline struct bset *btree_bset_first(struct btree *b)
 {
     return b->keys.set->data;
 }
 
 static inline struct bset *btree_bset_last(struct btree *b)
 {
     return bset_tree_last(&b->keys)->data;
 }
 
 static inline unsigned int bset_block_offset(struct btree *b, struct bset *i)
 {
     return bset_sector_offset(&b->keys, i) >> b->c->block_bits;
 }
 
 static inline void set_gc_sectors(struct cache_set *c)
 {
     atomic_set(&c->sectors_to_gc, c->cache->sb.bucket_size * c->nbuckets / 16);
 }
 
 void bkey_put(struct cache_set *c, struct bkey *k);
 
 /* Looping macros */
 
 #define for_each_cached_btree(b, c, iter)               \
     for (iter = 0;                          \
          iter < ARRAY_SIZE((c)->bucket_hash);           \
          iter++)                            \
         hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
 
 /* Recursing down the btree */
 
 struct btree_op {
     /* for waiting on btree reserve in btree_split() */
     wait_queue_entry_t      wait;
 
     /* Btree level at which we start taking write locks */
     short           lock;
 
     unsigned int        insert_collision:1;
 };
 
 struct btree_check_state;
 struct btree_check_info {
     struct btree_check_state    *state;
     struct task_struct      *thread;
     int             result;
 };
 
 #define BCH_BTR_CHKTHREAD_MAX   12
 struct btree_check_state {
     struct cache_set        *c;
     int             total_threads;
     int             key_idx;
     spinlock_t          idx_lock;
     atomic_t            started;
     atomic_t            enough;
     wait_queue_head_t       wait;
     struct btree_check_info     infos[BCH_BTR_CHKTHREAD_MAX];
 };
 
 static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level)
 {
     memset(op, 0, sizeof(struct btree_op));
     init_wait(&op->wait);
     op->lock = write_lock_level;
 }
 
 static inline void rw_lock(bool w, struct btree *b, int level)
 {
     w ? down_write_nested(&b->lock, level + 1)
       : down_read_nested(&b->lock, level + 1);
     if (w)
         b->seq++;
 }
 
 static inline void rw_unlock(bool w, struct btree *b)
 {
     if (w)
         b->seq++;
     (w ? up_write : up_read)(&b->lock);
 }
 
 void bch_btree_node_read_done(struct btree *b);
 void __bch_btree_node_write(struct btree *b, struct closure *parent);
 void bch_btree_node_write(struct btree *b, struct closure *parent);
 
 void bch_btree_set_root(struct btree *b);
 struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
                      int level, bool wait,
                      struct btree *parent);
 struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
                  struct bkey *k, int level, bool write,
                  struct btree *parent);
 
 int bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
                    struct bkey *check_key);
 int bch_btree_insert(struct cache_set *c, struct keylist *keys,
              atomic_t *journal_ref, struct bkey *replace_key);
 
 int bch_gc_thread_start(struct cache_set *c);
 void bch_initial_gc_finish(struct cache_set *c);
 void bch_moving_gc(struct cache_set *c);
 int bch_btree_check(struct cache_set *c);
 void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k);
 
 static inline void wake_up_gc(struct cache_set *c)
 {
     wake_up(&c->gc_wait);
 }
 
 static inline void force_wake_up_gc(struct cache_set *c)
 {
     /*
      * Garbage collection thread only works when sectors_to_gc < 0,
      * calling wake_up_gc() won't start gc thread if sectors_to_gc is
      * not a nagetive value.
      * Therefore sectors_to_gc is set to -1 here, before waking up
      * gc thread by calling wake_up_gc(). Then gc_should_run() will
      * give a chance to permit gc thread to run. "Give a chance" means
      * before going into gc_should_run(), there is still possibility
      * that c->sectors_to_gc being set to other positive value. So
      * this routine won't 100% make sure gc thread will be woken up
      * to run.
      */
     atomic_set(&c->sectors_to_gc, -1);
     wake_up_gc(c);
 }
 
 /*
  * These macros are for recursing down the btree - they handle the details of
  * locking and looking up nodes in the cache for you. They're best treated as
  * mere syntax when reading code that uses them.
  *
  * op->lock determines whether we take a read or a write lock at a given depth.
  * If you've got a read lock and find that you need a write lock (i.e. you're
  * going to have to split), set op->lock and return -EINTR; btree_root() will
  * call you again and you'll have the correct lock.
  */
 
 /**
  * btree - recurse down the btree on a specified key
  * @fn:     function to call, which will be passed the child node
  * @key:    key to recurse on
  * @b:      parent btree node
  * @op:     pointer to struct btree_op
  */
 #define bcache_btree(fn, key, b, op, ...)               \
 ({                                  \
     int _r, l = (b)->level - 1;                 \
     bool _w = l <= (op)->lock;                  \
     struct btree *_child = bch_btree_node_get((b)->c, op, key, l,   \
                           _w, b);       \
     if (!IS_ERR(_child)) {                      \
         _r = bch_btree_ ## fn(_child, op, ##__VA_ARGS__);   \
         rw_unlock(_w, _child);                  \
     } else                              \
         _r = PTR_ERR(_child);                   \
     _r;                             \
 })
 
 /**
  * btree_root - call a function on the root of the btree
  * @fn:     function to call, which will be passed the child node
  * @c:      cache set
  * @op:     pointer to struct btree_op
  */
 #define bcache_btree_root(fn, c, op, ...)               \
 ({                                  \
     int _r = -EINTR;                        \
     do {                                \
         struct btree *_b = (c)->root;               \
         bool _w = insert_lock(op, _b);              \
         rw_lock(_w, _b, _b->level);             \
         if (_b == (c)->root &&                  \
             _w == insert_lock(op, _b)) {            \
             _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__);   \
         }                           \
         rw_unlock(_w, _b);                  \
         bch_cannibalize_unlock(c);                              \
         if (_r == -EINTR)                                       \
             schedule();                                     \
     } while (_r == -EINTR);                                         \
                                     \
     finish_wait(&(c)->btree_cache_wait, &(op)->wait);               \
     _r;                                                             \
 })
 
 #define MAP_DONE    0
 #define MAP_CONTINUE    1
 
 #define MAP_ALL_NODES   0
 #define MAP_LEAF_NODES  1
 
 #define MAP_END_KEY 1
 
 typedef int (btree_map_nodes_fn)(struct btree_op *b_op, struct btree *b);
 int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
               struct bkey *from, btree_map_nodes_fn *fn, int flags);
 
 static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
                       struct bkey *from, btree_map_nodes_fn *fn)
 {
     return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
 }
 
 static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
                        struct cache_set *c,
                        struct bkey *from,
                        btree_map_nodes_fn *fn)
 {
     return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
 }
 
 typedef int (btree_map_keys_fn)(struct btree_op *op, struct btree *b,
                 struct bkey *k);
 int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
                struct bkey *from, btree_map_keys_fn *fn, int flags);
 int bch_btree_map_keys_recurse(struct btree *b, struct btree_op *op,
                    struct bkey *from, btree_map_keys_fn *fn,
                    int flags);
 
 typedef bool (keybuf_pred_fn)(struct keybuf *buf, struct bkey *k);
 
 void bch_keybuf_init(struct keybuf *buf);
 void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
                struct bkey *end, keybuf_pred_fn *pred);
 bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start,
                   struct bkey *end);
 void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w);
 struct keybuf_key *bch_keybuf_next(struct keybuf *buf);
 struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
                       struct keybuf *buf,
                       struct bkey *end,
                       keybuf_pred_fn *pred);
 void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats);
 #endif

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