+static int check_snapshot_tree(struct btree_trans *trans,
+ struct btree_iter *iter,
+ struct bkey_s_c k)
+{
+ struct bch_fs *c = trans->c;
+ struct bkey_s_c_snapshot_tree st;
+ struct bch_snapshot s;
+ struct bch_subvolume subvol;
+ struct printbuf buf = PRINTBUF;
+ u32 root_id;
+ int ret;
+
+ if (k.k->type != KEY_TYPE_snapshot_tree)
+ return 0;
+
+ st = bkey_s_c_to_snapshot_tree(k);
+ root_id = le32_to_cpu(st.v->root_snapshot);
+
+ ret = snapshot_lookup(trans, root_id, &s);
+ if (ret && !bch2_err_matches(ret, ENOENT))
+ goto err;
+
+ if (fsck_err_on(ret ||
+ root_id != bch2_snapshot_root(c, root_id) ||
+ st.k->p.offset != le32_to_cpu(s.tree),
+ c,
+ "snapshot tree points to missing/incorrect snapshot:\n %s",
+ (bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf))) {
+ ret = bch2_btree_delete_at(trans, iter, 0);
+ goto err;
+ }
+
+ ret = bch2_subvolume_get(trans, le32_to_cpu(st.v->master_subvol),
+ false, 0, &subvol);
+ if (ret && !bch2_err_matches(ret, ENOENT))
+ goto err;
+
+ if (fsck_err_on(ret, c,
+ "snapshot tree points to missing subvolume:\n %s",
+ (printbuf_reset(&buf),
+ bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf)) ||
+ fsck_err_on(!bch2_snapshot_is_ancestor_early(c,
+ le32_to_cpu(subvol.snapshot),
+ root_id), c,
+ "snapshot tree points to subvolume that does not point to snapshot in this tree:\n %s",
+ (printbuf_reset(&buf),
+ bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf)) ||
+ fsck_err_on(BCH_SUBVOLUME_SNAP(&subvol), c,
+ "snapshot tree points to snapshot subvolume:\n %s",
+ (printbuf_reset(&buf),
+ bch2_bkey_val_to_text(&buf, c, st.s_c), buf.buf))) {
+ struct bkey_i_snapshot_tree *u;
+ u32 subvol_id;
+
+ ret = bch2_snapshot_tree_master_subvol(trans, root_id, &subvol_id);
+ if (ret)
+ goto err;
+
+ u = bch2_bkey_make_mut_typed(trans, iter, &k, 0, snapshot_tree);
+ ret = PTR_ERR_OR_ZERO(u);
+ if (ret)
+ goto err;
+
+ u->v.master_subvol = cpu_to_le32(subvol_id);
+ st = snapshot_tree_i_to_s_c(u);
+ }
+err:
+fsck_err:
+ printbuf_exit(&buf);
+ return ret;
+}
+
+/*
+ * For each snapshot_tree, make sure it points to the root of a snapshot tree
+ * and that snapshot entry points back to it, or delete it.
+ *
+ * And, make sure it points to a subvolume within that snapshot tree, or correct
+ * it to point to the oldest subvolume within that snapshot tree.
+ */
+int bch2_check_snapshot_trees(struct bch_fs *c)