bcachefs: Key cache now works for snapshots btrees

This switches btree_key_cache_fill() to use a btree iterator, not a
btree path, so that it can search for keys in previous snapshots.

We also add another iterator flag, BTREE_ITER_KEY_CACHE_FILL, to avoid
recursion back into the key cache.

This will allow us to re-enable the key cache for inodes in the next
patch.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1855,6 +1855,10 @@ struct bkey_s_c btree_trans_peek_key_cache(struct btree_iter *iter, struct bpos
 	struct bkey_s_c k;
 	int ret;
 
+	if ((iter->flags & BTREE_ITER_KEY_CACHE_FILL) &&
+	    bpos_eq(iter->pos, pos))
+		return bkey_s_c_null;
+
 	if (!bch2_btree_key_cache_find(c, iter->btree_id, pos))
 		return bkey_s_c_null;
 

fs/bcachefs/btree_key_cache.c

@@ -370,20 +370,20 @@ static int btree_key_cache_fill(struct btree_trans *trans,
 				struct btree_path *ck_path,
 				struct bkey_cached *ck)
 {
-	struct btree_path *path;
+	struct btree_iter iter;
 	struct bkey_s_c k;
 	unsigned new_u64s = 0;
 	struct bkey_i *new_k = NULL;
-	struct bkey u;
 	int ret;
 
-	path = bch2_path_get(trans, ck->key.btree_id, ck->key.pos, 0, 0, 0);
-	ret = bch2_btree_path_traverse(trans, path, 0);
+	bch2_trans_iter_init(trans, &iter, ck->key.btree_id, ck->key.pos,
+			     BTREE_ITER_KEY_CACHE_FILL|
+			     BTREE_ITER_CACHED_NOFILL);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
 	if (ret)
 		goto err;
 
-	k = bch2_btree_path_peek_slot(path, &u);
-
 	if (!bch2_btree_node_relock(trans, ck_path, 0)) {
 		trace_and_count(trans->c, trans_restart_relock_key_cache_fill, trans, _THIS_IP_, ck_path);
 		ret = btree_trans_restart(trans, BCH_ERR_transaction_restart_key_cache_raced);
@@ -431,9 +431,9 @@ 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: */
-	path->preserve = false;
+	set_btree_iter_dontneed(&iter);
 err:
-	bch2_path_put(trans, path, 0);
+	bch2_trans_iter_exit(trans, &iter);
 	return ret;
 }
 

fs/bcachefs/btree_types.h

@@ -208,6 +208,7 @@ struct btree_node_iter {
 #define BTREE_ITER_FILTER_SNAPSHOTS	(1 << 12)
 #define BTREE_ITER_NOPRESERVE		(1 << 13)
 #define BTREE_ITER_CACHED_NOFILL	(1 << 14)
+#define BTREE_ITER_KEY_CACHE_FILL	(1 << 15)
 
 enum btree_path_uptodate {
 	BTREE_ITER_UPTODATE		= 0,

fs/bcachefs/inode.c

@@ -684,8 +684,8 @@ int bch2_inode_rm(struct bch_fs *c, subvol_inum inum)
 
 	if (!bkey_is_inode(k.k)) {
 		bch2_fs_inconsistent(trans.c,
-				     "inode %llu not found when deleting",
-				     inum.inum);
+				     "inode %llu:%u not found when deleting",
+				     inum.inum, snapshot);
 		ret = -EIO;
 		goto err;
 	}