bcachefs: Repair pass for scanning for btree nodes

If a btree root or interior btree node goes bad, we're going to lose a
lot of data, unless we can recover the nodes that it pointed to by
scanning.

Fortunately btree node headers are fully self describing, and
additionally the magic number is xored with the filesytem UUID, so we
can do so safely.

This implements the scanning - next patch will rework topology repair to
make use of the found nodes.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 30 insertions, 0 deletions

diff --git a/fs/bcachefs/btree_node_scan_types.h b/fs/bcachefs/btree_node_scan_types.h
new file mode 100644
index 000000000000..abb7b27d556a
--- /dev/null
+++ b/fs/bcachefs/btree_node_scan_types.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_BTREE_NODE_SCAN_TYPES_H
+#define _BCACHEFS_BTREE_NODE_SCAN_TYPES_H
+
+#include "darray.h"
+
+struct found_btree_node {
+	bool			range_updated:1;
+	bool			overwritten:1;
+	u8			btree_id;
+	u8			level;
+	u32			seq;
+	u64			cookie;
+
+	struct bpos		min_key;
+	struct bpos		max_key;
+
+	unsigned		nr_ptrs;
+	struct bch_extent_ptr	ptrs[BCH_REPLICAS_MAX];
+};
+
+typedef DARRAY(struct found_btree_node)	found_btree_nodes;
+
+struct find_btree_nodes {
+	int			ret;
+	struct mutex		lock;
+	found_btree_nodes	nodes;
+};
+
+#endif /* _BCACHEFS_BTREE_NODE_SCAN_TYPES_H */