bcache in userspace; userspace fsck

1 files changed, 1150 insertions, 0 deletions

diff --git a/libbcache/btree_iter.c b/libbcache/btree_iter.c
new file mode 100644
index 0000000..a9859e3
--- /dev/null
+++ b/libbcache/btree_iter.c
@@ -0,0 +1,1150 @@
+
+#include "bcache.h"
+#include "bkey_methods.h"
+#include "btree_cache.h"
+#include "btree_iter.h"
+#include "btree_locking.h"
+#include "debug.h"
+#include "extents.h"
+
+#include <trace/events/bcache.h>
+
+#define BTREE_ITER_NOT_END	((struct btree *) 1)
+
+static inline bool is_btree_node(struct btree_iter *iter, unsigned l)
+{
+	return iter->nodes[l] && iter->nodes[l] != BTREE_ITER_NOT_END;
+}
+
+/* Btree node locking: */
+
+/*
+ * Updates the saved lock sequence number, so that btree_node_relock() will
+ * succeed:
+ */
+void btree_node_unlock_write(struct btree *b, struct btree_iter *iter)
+{
+	struct btree_iter *linked;
+
+	EBUG_ON(iter->nodes[b->level] != b);
+	EBUG_ON(iter->lock_seq[b->level] + 1 != b->lock.state.seq);
+
+	for_each_linked_btree_node(iter, b, linked)
+		linked->lock_seq[b->level] += 2;
+
+	iter->lock_seq[b->level] += 2;
+
+	six_unlock_write(&b->lock);
+}
+
+void btree_node_lock_write(struct btree *b, struct btree_iter *iter)
+{
+	struct btree_iter *linked;
+	unsigned readers = 0;
+
+	EBUG_ON(iter->nodes[b->level] != b);
+	EBUG_ON(iter->lock_seq[b->level] != b->lock.state.seq);
+
+	if (six_trylock_write(&b->lock))
+		return;
+
+	for_each_linked_btree_iter(iter, linked)
+		if (linked->nodes[b->level] == b &&
+		    btree_node_read_locked(linked, b->level))
+			readers++;
+
+	if (likely(!readers)) {
+		six_lock_write(&b->lock);
+	} else {
+		/*
+		 * Must drop our read locks before calling six_lock_write() -
+		 * six_unlock() won't do wakeups until the reader count
+		 * goes to 0, and it's safe because we have the node intent
+		 * locked:
+		 */
+		atomic64_sub(__SIX_VAL(read_lock, readers),
+			     &b->lock.state.counter);
+		six_lock_write(&b->lock);
+		atomic64_add(__SIX_VAL(read_lock, readers),
+			     &b->lock.state.counter);
+	}
+}
+
+/* versions that allow iter to be null: */
+void __btree_node_unlock_write(struct btree *b, struct btree_iter *iter)
+{
+	if (likely(iter))
+		btree_node_unlock_write(b, iter);
+	else
+		six_unlock_write(&b->lock);
+}
+
+void __btree_node_lock_write(struct btree *b, struct btree_iter *iter)
+{
+	if (likely(iter))
+		btree_node_lock_write(b, iter);
+	else
+		six_lock_write(&b->lock);
+}
+
+bool btree_node_relock(struct btree_iter *iter, unsigned level)
+{
+	struct btree_iter *linked;
+	struct btree *b = iter->nodes[level];
+	enum btree_node_locked_type want = btree_lock_want(iter, level);
+	enum btree_node_locked_type have = btree_node_locked_type(iter, level);
+
+	if (want == have)
+		return true;
+
+	if (!is_btree_node(iter, level))
+		return false;
+
+	if (race_fault())
+		return false;
+
+	if (have != BTREE_NODE_UNLOCKED
+	    ? six_trylock_convert(&b->lock, have, want)
+	    : six_relock_type(&b->lock, want, iter->lock_seq[level]))
+		goto success;
+
+	for_each_linked_btree_iter(iter, linked)
+		if (linked->nodes[level] == b &&
+		    btree_node_locked_type(linked, level) == want &&
+		    iter->lock_seq[level] == b->lock.state.seq) {
+			btree_node_unlock(iter, level);
+			six_lock_increment(&b->lock, want);
+			goto success;
+		}
+
+	return false;
+success:
+	mark_btree_node_unlocked(iter, level);
+	mark_btree_node_locked(iter, level, want);
+	return true;
+}
+
+/* Slowpath: */
+bool __bch_btree_node_lock(struct btree *b, struct bpos pos,
+			   unsigned level,
+			   struct btree_iter *iter,
+			   enum six_lock_type type)
+{
+	struct btree_iter *linked;
+
+	/* Can't have children locked before ancestors: */
+	EBUG_ON(iter->nodes_locked && level > __ffs(iter->nodes_locked));
+
+	/*
+	 * Can't hold any read locks while we block taking an intent lock - see
+	 * below for reasoning, and we should have already dropped any read
+	 * locks in the current iterator
+	 */
+	EBUG_ON(type == SIX_LOCK_intent &&
+		iter->nodes_locked != iter->nodes_intent_locked);
+
+	for_each_linked_btree_iter(iter, linked)
+		if (linked->nodes[level] == b &&
+		    btree_node_locked_type(linked, level) == type) {
+			six_lock_increment(&b->lock, type);
+			return true;
+		}
+
+	/*
+	 * Must lock btree nodes in key order - this case hapens when locking
+	 * the prev sibling in btree node merging:
+	 */
+	if (iter->nodes_locked &&
+	    __ffs(iter->nodes_locked) == level &&
+	    __btree_iter_cmp(iter->btree_id, pos, iter))
+		return false;
+
+	for_each_linked_btree_iter(iter, linked) {
+		if (!linked->nodes_locked)
+			continue;
+
+		/*
+		 * Can't block taking an intent lock if we have _any_ nodes read
+		 * locked:
+		 *
+		 * - Our read lock blocks another thread with an intent lock on
+		 *   the same node from getting a write lock, and thus from
+		 *   dropping its intent lock
+		 *
+		 * - And the other thread may have multiple nodes intent locked:
+		 *   both the node we want to intent lock, and the node we
+		 *   already have read locked - deadlock:
+		 */
+		if (type == SIX_LOCK_intent &&
+		    linked->nodes_locked != linked->nodes_intent_locked) {
+			linked->locks_want = max(linked->locks_want,
+						 iter->locks_want);
+			return false;
+		}
+
+		/* We have to lock btree nodes in key order: */
+		if (__btree_iter_cmp(iter->btree_id, pos, linked) < 0)
+			return false;
+
+		/*
+		 * Interior nodes must be locked before their descendants: if
+		 * another iterator has possible descendants locked of the node
+		 * we're about to lock, it must have the ancestors locked too:
+		 */
+		if (linked->btree_id == iter->btree_id &&
+		    level > __fls(linked->nodes_locked)) {
+			linked->locks_want = max(linked->locks_want,
+						 iter->locks_want);
+			return false;
+		}
+	}
+
+	six_lock_type(&b->lock, type);
+	return true;
+}
+
+/* Btree iterator locking: */
+
+
+static void btree_iter_drop_extra_locks(struct btree_iter *iter)
+{
+	unsigned l;
+
+	while (iter->nodes_locked &&
+	       (l = __fls(iter->nodes_locked)) > iter->locks_want) {
+		if (!btree_node_locked(iter, l))
+			panic("l %u nodes_locked %u\n", l, iter->nodes_locked);
+
+		if (l > iter->level) {
+			btree_node_unlock(iter, l);
+		} else if (btree_node_intent_locked(iter, l)) {
+			six_lock_downgrade(&iter->nodes[l]->lock);
+			iter->nodes_intent_locked ^= 1 << l;
+		}
+	}
+}
+
+bool __bch_btree_iter_set_locks_want(struct btree_iter *iter,
+				     unsigned new_locks_want)
+{
+	struct btree_iter *linked;
+	unsigned l;
+
+	/* Drop locks we don't want anymore: */
+	if (new_locks_want < iter->locks_want)
+		for_each_linked_btree_iter(iter, linked)
+			if (linked->locks_want > new_locks_want) {
+				linked->locks_want = max_t(unsigned, 1,
+							   new_locks_want);
+				btree_iter_drop_extra_locks(linked);
+			}
+
+	iter->locks_want = new_locks_want;
+	btree_iter_drop_extra_locks(iter);
+
+	for (l = iter->level; l < iter->locks_want && iter->nodes[l]; l++)
+		if (!btree_node_relock(iter, l))
+			goto fail;
+
+	return true;
+fail:
+	/*
+	 * Just an optimization: ancestor nodes must be locked before child
+	 * nodes, so set locks_want on iterators that might lock ancestors
+	 * before us to avoid getting -EINTR later:
+	 */
+	for_each_linked_btree_iter(iter, linked)
+		if (linked->btree_id == iter->btree_id &&
+		    btree_iter_cmp(linked, iter) <= 0)
+			linked->locks_want = max_t(unsigned, linked->locks_want,
+						   new_locks_want);
+	return false;
+}
+
+static int __bch_btree_iter_unlock(struct btree_iter *iter)
+{
+	BUG_ON(iter->error == -EINTR);
+
+	while (iter->nodes_locked)
+		btree_node_unlock(iter, __ffs(iter->nodes_locked));
+
+	return iter->error;
+}
+
+int bch_btree_iter_unlock(struct btree_iter *iter)
+{
+	struct btree_iter *linked;
+
+	for_each_linked_btree_iter(iter, linked)
+		__bch_btree_iter_unlock(linked);
+	return __bch_btree_iter_unlock(iter);
+}
+
+/* Btree iterator: */
+
+#ifdef CONFIG_BCACHE_DEBUG
+
+static void __bch_btree_iter_verify(struct btree_iter *iter,
+				    struct btree *b)
+{
+	struct btree_node_iter *node_iter = &iter->node_iters[b->level];
+	struct btree_node_iter tmp = *node_iter;
+	struct bkey_packed *k;
+
+	bch_btree_node_iter_verify(node_iter, b);
+
+	/*
+	 * For interior nodes, the iterator will have skipped past
+	 * deleted keys:
+	 */
+	k = b->level
+		? bch_btree_node_iter_prev(&tmp, b)
+		: bch_btree_node_iter_prev_all(&tmp, b);
+	if (k && btree_iter_pos_cmp_packed(b, &iter->pos, k,
+					   iter->is_extents)) {
+		char buf[100];
+		struct bkey uk = bkey_unpack_key(b, k);
+
+		bch_bkey_to_text(buf, sizeof(buf), &uk);
+		panic("prev key should be before after pos:\n%s\n%llu:%llu\n",
+		      buf, iter->pos.inode, iter->pos.offset);
+	}
+
+	k = bch_btree_node_iter_peek_all(node_iter, b);
+	if (k && !btree_iter_pos_cmp_packed(b, &iter->pos, k,
+					    iter->is_extents)) {
+		char buf[100];
+		struct bkey uk = bkey_unpack_key(b, k);
+
+		bch_bkey_to_text(buf, sizeof(buf), &uk);
+		panic("next key should be before iter pos:\n%llu:%llu\n%s\n",
+		      iter->pos.inode, iter->pos.offset, buf);
+	}
+}
+
+void bch_btree_iter_verify(struct btree_iter *iter, struct btree *b)
+{
+	struct btree_iter *linked;
+
+	if (iter->nodes[b->level] == b)
+		__bch_btree_iter_verify(iter, b);
+
+	for_each_linked_btree_node(iter, b, linked)
+		__bch_btree_iter_verify(iter, b);
+}
+
+#endif
+
+static void __bch_btree_node_iter_fix(struct btree_iter *iter,
+				      struct btree *b,
+				      struct btree_node_iter *node_iter,
+				      struct bset_tree *t,
+				      struct bkey_packed *where,
+				      unsigned clobber_u64s,
+				      unsigned new_u64s)
+{
+	const struct bkey_packed *end = btree_bkey_last(b, t);
+	struct btree_node_iter_set *set;
+	unsigned offset = __btree_node_key_to_offset(b, where);
+	int shift = new_u64s - clobber_u64s;
+	unsigned old_end = (int) __btree_node_key_to_offset(b, end) - shift;
+
+	btree_node_iter_for_each(node_iter, set)
+		if (set->end == old_end)
+			goto found;
+
+	/* didn't find the bset in the iterator - might have to readd it: */
+	if (new_u64s &&
+	    btree_iter_pos_cmp_packed(b, &iter->pos, where,
+				      iter->is_extents))
+		bch_btree_node_iter_push(node_iter, b, where, end);
+	return;
+found:
+	set->end = (int) set->end + shift;
+
+	/* Iterator hasn't gotten to the key that changed yet: */
+	if (set->k < offset)
+		return;
+
+	if (new_u64s &&
+	    btree_iter_pos_cmp_packed(b, &iter->pos, where,
+				      iter->is_extents)) {
+		set->k = offset;
+		bch_btree_node_iter_sort(node_iter, b);
+	} else if (set->k < offset + clobber_u64s) {
+		set->k = offset + new_u64s;
+		if (set->k == set->end)
+			*set = node_iter->data[--node_iter->used];
+		bch_btree_node_iter_sort(node_iter, b);
+	} else {
+		set->k = (int) set->k + shift;
+	}
+
+	/*
+	 * Interior nodes are special because iterators for interior nodes don't
+	 * obey the usual invariants regarding the iterator position:
+	 *
+	 * We may have whiteouts that compare greater than the iterator
+	 * position, and logically should be in the iterator, but that we
+	 * skipped past to find the first live key greater than the iterator
+	 * position. This becomes an issue when we insert a new key that is
+	 * greater than the current iterator position, but smaller than the
+	 * whiteouts we've already skipped past - this happens in the course of
+	 * a btree split.
+	 *
+	 * We have to rewind the iterator past to before those whiteouts here,
+	 * else bkey_node_iter_prev() is not going to work and who knows what
+	 * else would happen. And we have to do it manually, because here we've
+	 * already done the insert and the iterator is currently inconsistent:
+	 *
+	 * We've got multiple competing invariants, here - we have to be careful
+	 * about rewinding iterators for interior nodes, because they should
+	 * always point to the key for the child node the btree iterator points
+	 * to.
+	 */
+	if (b->level && new_u64s && !bkey_deleted(where) &&
+	    btree_iter_pos_cmp_packed(b, &iter->pos, where,
+				      iter->is_extents)) {
+		struct bset_tree *t;
+		struct bkey_packed *k;
+
+		for_each_bset(b, t) {
+			if (bch_bkey_to_bset(b, where) == t)
+				continue;
+
+			k = bkey_prev_all(b, t,
+				bch_btree_node_iter_bset_pos(node_iter, b, t));
+			if (k &&
+			    __btree_node_iter_cmp(node_iter, b,
+						  k, where) > 0) {
+				struct btree_node_iter_set *set;
+				unsigned offset =
+					__btree_node_key_to_offset(b, bkey_next(k));
+
+				btree_node_iter_for_each(node_iter, set)
+					if (set->k == offset) {
+						set->k = __btree_node_key_to_offset(b, k);
+						bch_btree_node_iter_sort(node_iter, b);
+						goto next_bset;
+					}
+
+				bch_btree_node_iter_push(node_iter, b, k,
+						btree_bkey_last(b, t));
+			}
+next_bset:
+			t = t;
+		}
+	}
+}
+
+void bch_btree_node_iter_fix(struct btree_iter *iter,
+			     struct btree *b,
+			     struct btree_node_iter *node_iter,
+			     struct bset_tree *t,
+			     struct bkey_packed *where,
+			     unsigned clobber_u64s,
+			     unsigned new_u64s)
+{
+	struct btree_iter *linked;
+
+	if (node_iter != &iter->node_iters[b->level])
+		__bch_btree_node_iter_fix(iter, b, node_iter, t,
+					  where, clobber_u64s, new_u64s);
+
+	if (iter->nodes[b->level] == b)
+		__bch_btree_node_iter_fix(iter, b,
+					  &iter->node_iters[b->level], t,
+					  where, clobber_u64s, new_u64s);
+
+	for_each_linked_btree_node(iter, b, linked)
+		__bch_btree_node_iter_fix(linked, b,
+					  &linked->node_iters[b->level], t,
+					  where, clobber_u64s, new_u64s);
+
+	/* interior node iterators are... special... */
+	if (!b->level)
+		bch_btree_iter_verify(iter, b);
+}
+
+/* peek_all() doesn't skip deleted keys */
+static inline struct bkey_s_c __btree_iter_peek_all(struct btree_iter *iter)
+{
+	struct btree *b = iter->nodes[iter->level];
+	struct bkey_packed *k =
+		bch_btree_node_iter_peek_all(&iter->node_iters[iter->level], b);
+	struct bkey_s_c ret;
+
+	EBUG_ON(!btree_node_locked(iter, iter->level));
+
+	if (!k)
+		return bkey_s_c_null;
+
+	ret = bkey_disassemble(b, k, &iter->k);
+
+	if (debug_check_bkeys(iter->c))
+		bkey_debugcheck(iter->c, b, ret);
+
+	return ret;
+}
+
+static inline struct bkey_s_c __btree_iter_peek(struct btree_iter *iter)
+{
+	struct btree *b = iter->nodes[iter->level];
+	struct bkey_packed *k =
+		bch_btree_node_iter_peek(&iter->node_iters[iter->level], b);
+	struct bkey_s_c ret;
+
+	EBUG_ON(!btree_node_locked(iter, iter->level));
+
+	if (!k)
+		return bkey_s_c_null;
+
+	ret = bkey_disassemble(b, k, &iter->k);
+
+	if (debug_check_bkeys(iter->c))
+		bkey_debugcheck(iter->c, b, ret);
+
+	return ret;
+}
+
+static inline void __btree_iter_advance(struct btree_iter *iter)
+{
+	bch_btree_node_iter_advance(&iter->node_iters[iter->level],
+				    iter->nodes[iter->level]);
+}
+
+/*
+ * Verify that iterator for parent node points to child node:
+ */
+static void btree_iter_verify_new_node(struct btree_iter *iter, struct btree *b)
+{
+	bool parent_locked;
+	struct bkey_packed *k;
+
+	if (!IS_ENABLED(CONFIG_BCACHE_DEBUG) ||
+	    !iter->nodes[b->level + 1])
+		return;
+
+	parent_locked = btree_node_locked(iter, b->level + 1);
+
+	if (!btree_node_relock(iter, b->level + 1))
+		return;
+
+	k = bch_btree_node_iter_peek_all(&iter->node_iters[b->level + 1],
+					 iter->nodes[b->level + 1]);
+	if (!k ||
+	    bkey_deleted(k) ||
+	    bkey_cmp_left_packed(iter->nodes[b->level + 1],
+				 k, &b->key.k.p)) {
+		char buf[100];
+		struct bkey uk = bkey_unpack_key(b, k);
+
+		bch_bkey_to_text(buf, sizeof(buf), &uk);
+		panic("parent iter doesn't point to new node:\n%s\n%llu:%llu\n",
+		      buf, b->key.k.p.inode, b->key.k.p.offset);
+	}
+
+	if (!parent_locked)
+		btree_node_unlock(iter, b->level + 1);
+}
+
+static inline void __btree_iter_init(struct btree_iter *iter,
+				     struct btree *b)
+{
+	bch_btree_node_iter_init(&iter->node_iters[b->level], b,
+				 iter->pos, iter->is_extents,
+				 btree_node_is_extents(b));
+
+	/* Skip to first non whiteout: */
+	if (b->level)
+		bch_btree_node_iter_peek(&iter->node_iters[b->level], b);
+}
+
+static inline bool btree_iter_pos_in_node(struct btree_iter *iter,
+					  struct btree *b)
+{
+	return iter->btree_id == b->btree_id &&
+		bkey_cmp(iter->pos, b->data->min_key) >= 0 &&
+		btree_iter_pos_cmp(iter->pos, &b->key.k, iter->is_extents);
+}
+
+static inline void btree_iter_node_set(struct btree_iter *iter,
+				       struct btree *b)
+{
+	btree_iter_verify_new_node(iter, b);
+
+	EBUG_ON(!btree_iter_pos_in_node(iter, b));
+	EBUG_ON(b->lock.state.seq & 1);
+
+	iter->lock_seq[b->level] = b->lock.state.seq;
+	iter->nodes[b->level] = b;
+	__btree_iter_init(iter, b);
+}
+
+/*
+ * A btree node is being replaced - update the iterator to point to the new
+ * node:
+ */
+bool bch_btree_iter_node_replace(struct btree_iter *iter, struct btree *b)
+{
+	struct btree_iter *linked;
+
+	for_each_linked_btree_iter(iter, linked)
+		if (btree_iter_pos_in_node(linked, b)) {
+			/*
+			 * bch_btree_iter_node_drop() has already been called -
+			 * the old node we're replacing has already been
+			 * unlocked and the pointer invalidated
+			 */
+			BUG_ON(btree_node_locked(linked, b->level));
+
+			/*
+			 * If @linked wants this node read locked, we don't want
+			 * to actually take the read lock now because it's not
+			 * legal to hold read locks on other nodes while we take
+			 * write locks, so the journal can make forward
+			 * progress...
+			 *
+			 * Instead, btree_iter_node_set() sets things up so
+			 * btree_node_relock() will succeed:
+			 */
+
+			if (btree_want_intent(linked, b->level)) {
+				six_lock_increment(&b->lock, SIX_LOCK_intent);
+				mark_btree_node_intent_locked(linked, b->level);
+			}
+
+			btree_iter_node_set(linked, b);
+		}
+
+	if (!btree_iter_pos_in_node(iter, b)) {
+		six_unlock_intent(&b->lock);
+		return false;
+	}
+
+	mark_btree_node_intent_locked(iter, b->level);
+	btree_iter_node_set(iter, b);
+	return true;
+}
+
+void bch_btree_iter_node_drop_linked(struct btree_iter *iter, struct btree *b)
+{
+	struct btree_iter *linked;
+	unsigned level = b->level;
+
+	for_each_linked_btree_iter(iter, linked)
+		if (linked->nodes[level] == b) {
+			btree_node_unlock(linked, level);
+			linked->nodes[level] = BTREE_ITER_NOT_END;
+		}
+}
+
+void bch_btree_iter_node_drop(struct btree_iter *iter, struct btree *b)
+{
+	unsigned level = b->level;
+
+	if (iter->nodes[level] == b) {
+		BUG_ON(b->lock.state.intent_lock != 1);
+		btree_node_unlock(iter, level);
+		iter->nodes[level] = BTREE_ITER_NOT_END;
+	}
+}
+
+/*
+ * A btree node has been modified in such a way as to invalidate iterators - fix
+ * them:
+ */
+void bch_btree_iter_reinit_node(struct btree_iter *iter, struct btree *b)
+{
+	struct btree_iter *linked;
+
+	for_each_linked_btree_node(iter, b, linked)
+		__btree_iter_init(linked, b);
+	__btree_iter_init(iter, b);
+}
+
+static inline int btree_iter_lock_root(struct btree_iter *iter,
+				       unsigned depth_want)
+{
+	struct cache_set *c = iter->c;
+	struct btree *b;
+	enum six_lock_type lock_type;
+	unsigned i;
+
+	EBUG_ON(iter->nodes_locked);
+
+	while (1) {
+		b = READ_ONCE(c->btree_roots[iter->btree_id].b);
+		iter->level = READ_ONCE(b->level);
+
+		if (unlikely(iter->level < depth_want)) {
+			/*
+			 * the root is at a lower depth than the depth we want:
+			 * got to the end of the btree, or we're walking nodes
+			 * greater than some depth and there are no nodes >=
+			 * that depth
+			 */
+			iter->level = depth_want;
+			iter->nodes[iter->level] = NULL;
+			return 0;
+		}
+
+		lock_type = btree_lock_want(iter, iter->level);
+		if (unlikely(!btree_node_lock(b, POS_MAX, iter->level,
+					      iter, lock_type)))
+			return -EINTR;
+
+		if (likely(b == c->btree_roots[iter->btree_id].b &&
+			   b->level == iter->level &&
+			   !race_fault())) {
+			for (i = 0; i < iter->level; i++)
+				iter->nodes[i] = BTREE_ITER_NOT_END;
+			iter->nodes[iter->level] = b;
+
+			mark_btree_node_locked(iter, iter->level, lock_type);
+			btree_iter_node_set(iter, b);
+			return 0;
+
+		}
+
+		six_unlock_type(&b->lock, lock_type);
+	}
+}
+
+static inline int btree_iter_down(struct btree_iter *iter)
+{
+	struct btree *b;
+	struct bkey_s_c k = __btree_iter_peek(iter);
+	unsigned level = iter->level - 1;
+	enum six_lock_type lock_type = btree_lock_want(iter, level);
+	BKEY_PADDED(k) tmp;
+
+	bkey_reassemble(&tmp.k, k);
+
+	b = bch_btree_node_get(iter, &tmp.k, level, lock_type);
+	if (unlikely(IS_ERR(b)))
+		return PTR_ERR(b);
+
+	iter->level = level;
+	mark_btree_node_locked(iter, level, lock_type);
+	btree_iter_node_set(iter, b);
+	return 0;
+}
+
+static void btree_iter_up(struct btree_iter *iter)
+{
+	btree_node_unlock(iter, iter->level++);
+}
+
+int __must_check __bch_btree_iter_traverse(struct btree_iter *);
+
+static int btree_iter_traverse_error(struct btree_iter *iter, int ret)
+{
+	struct cache_set *c = iter->c;
+	struct btree_iter *linked, *sorted_iters, **i;
+retry_all:
+	bch_btree_iter_unlock(iter);
+
+	if (ret != -ENOMEM && ret != -EINTR)
+		goto io_error;
+
+	if (ret == -ENOMEM) {
+		struct closure cl;
+
+		closure_init_stack(&cl);
+
+		do {
+			ret = mca_cannibalize_lock(c, &cl);
+			closure_sync(&cl);
+		} while (ret);
+	}
+
+	/*
+	 * Linked iters are normally a circular singly linked list - break cycle
+	 * while we sort them:
+	 */
+	linked = iter->next;
+	iter->next = NULL;
+	sorted_iters = NULL;
+
+	while (linked) {
+		iter = linked;
+		linked = linked->next;
+
+		i = &sorted_iters;
+		while (*i && btree_iter_cmp(iter, *i) > 0)
+			i = &(*i)->next;
+
+		iter->next = *i;
+		*i = iter;
+	}
+
+	/* Make list circular again: */
+	iter = sorted_iters;
+	while (iter->next)
+		iter = iter->next;
+	iter->next = sorted_iters;
+
+	/* Now, redo traversals in correct order: */
+
+	iter = sorted_iters;
+	do {
+retry:
+		ret = __bch_btree_iter_traverse(iter);
+		if (unlikely(ret)) {
+			if (ret == -EINTR)
+				goto retry;
+			goto retry_all;
+		}
+
+		iter = iter->next;
+	} while (iter != sorted_iters);
+
+	ret = btree_iter_linked(iter) ? -EINTR : 0;
+out:
+	mca_cannibalize_unlock(c);
+	return ret;
+io_error:
+	BUG_ON(ret != -EIO);
+
+	iter->error = ret;
+	iter->nodes[iter->level] = NULL;
+	goto out;
+}
+
+/*
+ * This is the main state machine for walking down the btree - walks down to a
+ * specified depth
+ *
+ * Returns 0 on success, -EIO on error (error reading in a btree node).
+ *
+ * On error, caller (peek_node()/peek_key()) must return NULL; the error is
+ * stashed in the iterator and returned from bch_btree_iter_unlock().
+ */
+int __must_check __bch_btree_iter_traverse(struct btree_iter *iter)
+{
+	unsigned depth_want = iter->level;
+
+	/* make sure we have all the intent locks we need - ugh */
+	if (unlikely(iter->nodes[iter->level] &&
+		     iter->level + 1 < iter->locks_want)) {
+		unsigned i;
+
+		for (i = iter->level + 1;
+		     i < iter->locks_want && iter->nodes[i];
+		     i++)
+			if (!btree_node_relock(iter, i)) {
+				while (iter->nodes[iter->level] &&
+				       iter->level + 1 < iter->locks_want)
+					btree_iter_up(iter);
+				break;
+			}
+	}
+
+	/*
+	 * If the current node isn't locked, go up until we have a locked node
+	 * or run out of nodes:
+	 */
+	while (iter->nodes[iter->level] &&
+	       !(is_btree_node(iter, iter->level) &&
+		 btree_node_relock(iter, iter->level) &&
+		 btree_iter_pos_cmp(iter->pos,
+				    &iter->nodes[iter->level]->key.k,
+				    iter->is_extents)))
+		btree_iter_up(iter);
+
+	/*
+	 * If we've got a btree node locked (i.e. we aren't about to relock the
+	 * root) - advance its node iterator if necessary:
+	 */
+	if (iter->nodes[iter->level]) {
+		struct bkey_s_c k;
+
+		while ((k = __btree_iter_peek_all(iter)).k &&
+		       !btree_iter_pos_cmp(iter->pos, k.k, iter->is_extents))
+			__btree_iter_advance(iter);
+	}
+
+	/*
+	 * Note: iter->nodes[iter->level] may be temporarily NULL here - that
+	 * would indicate to other code that we got to the end of the btree,
+	 * here it indicates that relocking the root failed - it's critical that
+	 * btree_iter_lock_root() comes next and that it can't fail
+	 */
+	while (iter->level > depth_want) {
+		int ret = iter->nodes[iter->level]
+			? btree_iter_down(iter)
+			: btree_iter_lock_root(iter, depth_want);
+		if (unlikely(ret)) {
+			iter->level = depth_want;
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+int __must_check bch_btree_iter_traverse(struct btree_iter *iter)
+{
+	int ret;
+
+	if (unlikely(!iter->nodes[iter->level]))
+		return 0;
+
+	iter->at_end_of_leaf = false;
+
+	ret = __bch_btree_iter_traverse(iter);
+	if (unlikely(ret))
+		ret = btree_iter_traverse_error(iter, ret);
+
+	return ret;
+}
+
+/* Iterate across nodes (leaf and interior nodes) */
+
+struct btree *bch_btree_iter_peek_node(struct btree_iter *iter)
+{
+	struct btree *b;
+	int ret;
+
+	EBUG_ON(iter->is_extents);
+
+	ret = bch_btree_iter_traverse(iter);
+	if (ret)
+		return NULL;
+
+	b = iter->nodes[iter->level];
+
+	if (b) {
+		EBUG_ON(bkey_cmp(b->key.k.p, iter->pos) < 0);
+		iter->pos = b->key.k.p;
+	}
+
+	return b;
+}
+
+struct btree *bch_btree_iter_next_node(struct btree_iter *iter, unsigned depth)
+{
+	struct btree *b;
+	int ret;
+
+	EBUG_ON(iter->is_extents);
+
+	btree_iter_up(iter);
+
+	if (!iter->nodes[iter->level])
+		return NULL;
+
+	/* parent node usually won't be locked: redo traversal if necessary */
+	ret = bch_btree_iter_traverse(iter);
+	if (ret)
+		return NULL;
+
+	b = iter->nodes[iter->level];
+	if (!b)
+		return b;
+
+	if (bkey_cmp(iter->pos, b->key.k.p) < 0) {
+		/* Haven't gotten to the end of the parent node: */
+
+		/* ick: */
+		iter->pos	= iter->btree_id == BTREE_ID_INODES
+			? btree_type_successor(iter->btree_id, iter->pos)
+			: bkey_successor(iter->pos);
+		iter->level	= depth;
+
+		ret = bch_btree_iter_traverse(iter);
+		if (ret)
+			return NULL;
+
+		b = iter->nodes[iter->level];
+	}
+
+	iter->pos = b->key.k.p;
+
+	return b;
+}
+
+/* Iterate across keys (in leaf nodes only) */
+
+void bch_btree_iter_set_pos_same_leaf(struct btree_iter *iter, struct bpos new_pos)
+{
+	struct btree *b = iter->nodes[0];
+	struct btree_node_iter *node_iter = &iter->node_iters[0];
+	struct bkey_packed *k;
+
+	EBUG_ON(iter->level != 0);
+	EBUG_ON(bkey_cmp(new_pos, iter->pos) < 0);
+	EBUG_ON(!btree_node_locked(iter, 0));
+	EBUG_ON(bkey_cmp(new_pos, b->key.k.p) > 0);
+
+	while ((k = bch_btree_node_iter_peek_all(node_iter, b)) &&
+	       !btree_iter_pos_cmp_packed(b, &new_pos, k,
+					  iter->is_extents))
+		bch_btree_node_iter_advance(node_iter, b);
+
+	if (!k &&
+	    !btree_iter_pos_cmp(new_pos, &b->key.k, iter->is_extents))
+		iter->at_end_of_leaf = true;
+
+	iter->pos = new_pos;
+}
+
+void bch_btree_iter_set_pos(struct btree_iter *iter, struct bpos new_pos)
+{
+	EBUG_ON(bkey_cmp(new_pos, iter->pos) < 0); /* XXX handle this */
+	iter->pos = new_pos;
+}
+
+void bch_btree_iter_advance_pos(struct btree_iter *iter)
+{
+	/*
+	 * We use iter->k instead of iter->pos for extents: iter->pos will be
+	 * equal to the start of the extent we returned, but we need to advance
+	 * to the end of the extent we returned.
+	 */
+	bch_btree_iter_set_pos(iter,
+		btree_type_successor(iter->btree_id, iter->k.p));
+}
+
+/* XXX: expensive */
+void bch_btree_iter_rewind(struct btree_iter *iter, struct bpos pos)
+{
+	/* incapable of rewinding across nodes: */
+	BUG_ON(bkey_cmp(pos, iter->nodes[iter->level]->data->min_key) < 0);
+
+	iter->pos = pos;
+	__btree_iter_init(iter, iter->nodes[iter->level]);
+}
+
+struct bkey_s_c bch_btree_iter_peek(struct btree_iter *iter)
+{
+	struct bkey_s_c k;
+	int ret;
+
+	while (1) {
+		ret = bch_btree_iter_traverse(iter);
+		if (unlikely(ret)) {
+			iter->k = KEY(iter->pos.inode, iter->pos.offset, 0);
+			return bkey_s_c_err(ret);
+		}
+
+		k = __btree_iter_peek(iter);
+		if (likely(k.k)) {
+			/*
+			 * iter->pos should always be equal to the key we just
+			 * returned - except extents can straddle iter->pos:
+			 */
+			if (!iter->is_extents ||
+			    bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
+				bch_btree_iter_set_pos(iter, bkey_start_pos(k.k));
+			return k;
+		}
+
+		iter->pos = iter->nodes[0]->key.k.p;
+
+		if (!bkey_cmp(iter->pos, POS_MAX)) {
+			iter->k = KEY(iter->pos.inode, iter->pos.offset, 0);
+			bch_btree_iter_unlock(iter);
+			return bkey_s_c_null;
+		}
+
+		iter->pos = btree_type_successor(iter->btree_id, iter->pos);
+	}
+}
+
+struct bkey_s_c bch_btree_iter_peek_with_holes(struct btree_iter *iter)
+{
+	struct bkey_s_c k;
+	struct bkey n;
+	int ret;
+
+	while (1) {
+		ret = bch_btree_iter_traverse(iter);
+		if (unlikely(ret)) {
+			iter->k = KEY(iter->pos.inode, iter->pos.offset, 0);
+			return bkey_s_c_err(ret);
+		}
+
+		k = __btree_iter_peek_all(iter);
+recheck:
+		if (!k.k || bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0) {
+			/* hole */
+			bkey_init(&n);
+			n.p = iter->pos;
+
+			if (iter->is_extents) {
+				if (n.p.offset == KEY_OFFSET_MAX) {
+					iter->pos = bkey_successor(iter->pos);
+					goto recheck;
+				}
+
+				if (!k.k)
+					k.k = &iter->nodes[0]->key.k;
+
+				bch_key_resize(&n,
+				       min_t(u64, KEY_SIZE_MAX,
+					     (k.k->p.inode == n.p.inode
+					      ? bkey_start_offset(k.k)
+					      : KEY_OFFSET_MAX) -
+					     n.p.offset));
+
+				EBUG_ON(!n.size);
+			}
+
+			iter->k = n;
+			return (struct bkey_s_c) { &iter->k, NULL };
+		} else if (!bkey_deleted(k.k)) {
+			return k;
+		} else {
+			__btree_iter_advance(iter);
+		}
+	}
+}
+
+void __bch_btree_iter_init(struct btree_iter *iter, struct cache_set *c,
+			   enum btree_id btree_id, struct bpos pos,
+			   unsigned locks_want, unsigned depth)
+{
+	iter->level			= depth;
+	/* bch_bkey_ops isn't used much, this would be a cache miss */
+	/* iter->is_extents		= bch_bkey_ops[btree_id]->is_extents; */
+	iter->is_extents		= btree_id == BTREE_ID_EXTENTS;
+	iter->nodes_locked		= 0;
+	iter->nodes_intent_locked	= 0;
+	iter->locks_want		= min(locks_want, BTREE_MAX_DEPTH);
+	iter->btree_id			= btree_id;
+	iter->at_end_of_leaf		= 0;
+	iter->error			= 0;
+	iter->c				= c;
+	iter->pos			= pos;
+	memset(iter->nodes, 0, sizeof(iter->nodes));
+	iter->nodes[iter->level]	= BTREE_ITER_NOT_END;
+	iter->next			= iter;
+
+	prefetch(c->btree_roots[btree_id].b);
+}
+
+void bch_btree_iter_link(struct btree_iter *iter, struct btree_iter *new)
+{
+	BUG_ON(btree_iter_linked(new));
+
+	new->next = iter->next;
+	iter->next = new;
+
+	if (IS_ENABLED(CONFIG_BCACHE_DEBUG)) {
+		unsigned nr_iters = 1;
+
+		for_each_linked_btree_iter(iter, new)
+			nr_iters++;
+
+		BUG_ON(nr_iters > SIX_LOCK_MAX_RECURSE);
+	}
+}
+
+void bch_btree_iter_copy(struct btree_iter *dst, struct btree_iter *src)
+{
+	bch_btree_iter_unlock(dst);
+	memcpy(dst, src, offsetof(struct btree_iter, next));
+	dst->nodes_locked = dst->nodes_intent_locked = 0;
+}