bcachefs: BTREE_ITER_WITH_KEY_CACHE

This is the start of cache coherency with the btree key cache - this
adds a btree iterator flag that causes lookups to also check the key
cache when we're iterating over the btree (not iterating over the key
cache).

Note that we could still race with another thread creating at item in
the key cache and updating it, since we aren't holding the key cache
locked if it wasn't found. The next patch for the update path will
address this by causing the transaction to restart if the key cache is
found to be dirty.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/fs/bcachefs/btree_key_cache.c b/fs/bcachefs/btree_key_cache.c
index f43153bcbf2f..8bfdbbdbf7c8 100644
--- a/fs/bcachefs/btree_key_cache.c
+++ b/fs/bcachefs/btree_key_cache.c
@@ -208,19 +208,21 @@ static int btree_key_cache_fill(struct btree_trans *trans,
 				struct btree_path *ck_path,
 				struct bkey_cached *ck)
 {
-	struct btree_iter iter;
+	struct btree_path *path;
 	struct bkey_s_c k;
 	unsigned new_u64s = 0;
 	struct bkey_i *new_k = NULL;
+	struct bkey u;
 	int ret;
 
-	bch2_trans_iter_init(trans, &iter, ck->key.btree_id,
-			     ck->key.pos, BTREE_ITER_SLOTS);
-	k = bch2_btree_iter_peek_slot(&iter);
-	ret = bkey_err(k);
+	path = bch2_path_get(trans, ck->key.btree_id,
+			     ck->key.pos, 0, 0, 0, _THIS_IP_);
+	ret = bch2_btree_path_traverse(trans, path, 0);
 	if (ret)
 		goto err;
 
+	k = bch2_btree_path_peek_slot(path, &u);
+
 	if (!bch2_btree_node_relock(trans, ck_path, 0)) {
 		trace_trans_restart_relock_key_cache_fill(trans->fn,
 				_THIS_IP_, ck_path->btree_id, &ck_path->pos);
@@ -261,9 +263,9 @@ static int btree_key_cache_fill(struct btree_trans *trans,
 	bch2_btree_node_unlock_write(trans, ck_path, ck_path->l[0].b);
 
 	/* We're not likely to need this iterator again: */
-	set_btree_iter_dontneed(&iter);
+	path->preserve = false;
 err:
-	bch2_trans_iter_exit(trans, &iter);
+	bch2_path_put(trans, path, 0);
 	return ret;
 }
 
@@ -384,6 +386,8 @@ static int btree_key_cache_flush_pos(struct btree_trans *trans,
 			     BTREE_ITER_CACHED_NOFILL|
 			     BTREE_ITER_CACHED_NOCREATE|
 			     BTREE_ITER_INTENT);
+	b_iter.flags &= ~BTREE_ITER_WITH_KEY_CACHE;
+
 	ret = bch2_btree_iter_traverse(&c_iter);
 	if (ret)
 		goto out;