bcachefs: btree_root_unreadable_and_scan_found_nothing autofix for non data btrees

If loosing a btree won't cause data loss - i.e. it's an alloc btree, or
we can easily reconstruct it - we shouldn't require user action to
continue repair.

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

fs/bcachefs/btree_gc.c

@@ -47,6 +47,27 @@
 #define DROP_PREV_NODE		11
 #define DID_FILL_FROM_SCAN	12
 
+/*
+ * Returns true if it's a btree we can easily reconstruct, or otherwise won't
+ * cause data loss if it's missing:
+ */
+static bool btree_id_important(enum btree_id btree)
+{
+	if (btree_id_is_alloc(btree))
+		return false;
+
+	switch (btree) {
+	case BTREE_ID_quotas:
+	case BTREE_ID_snapshot_trees:
+	case BTREE_ID_logged_ops:
+	case BTREE_ID_rebalance_work:
+	case BTREE_ID_subvolume_children:
+		return false;
+	default:
+		return true;
+	}
+}
+
 static const char * const bch2_gc_phase_strs[] = {
 #define x(n)	#n,
 	GC_PHASES()
@@ -534,8 +555,10 @@ reconstruct_root:
 			r->error = 0;
 
 			if (!bch2_btree_has_scanned_nodes(c, i)) {
-				mustfix_fsck_err(trans, btree_root_unreadable_and_scan_found_nothing,
-						 "no nodes found for btree %s, continue?", buf.buf);
+				__fsck_err(trans,
+					   FSCK_CAN_FIX|(!btree_id_important(i) ? FSCK_AUTOFIX : 0),
+					   btree_root_unreadable_and_scan_found_nothing,
+					   "no nodes found for btree %s, continue?", buf.buf);
 				bch2_btree_root_alloc_fake_trans(trans, i, 0);
 			} else {
 				bch2_btree_root_alloc_fake_trans(trans, i, 1);