From: Vladimír Čunát <vladimir.cunat@nic.cz>
Date: Thu, 23 Apr 2026 08:50:28 +0000 (+0200)
Subject: lib/cache/cdb: add txn_open_rw()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=775f93ca3452b0d12dd25c13000bd1442dc40e41;p=thirdparty%2Fknot-resolver.git

lib/cache/cdb: add txn_open_rw()

This was extracted from jezek-test commit:
  lib/rules: make kr_rule_local_subtree() safer wrt. transactions

While we don't use this so far, picking will reduce conflicts
e.g. when moving changes between the branches.
---

diff --git a/lib/cache/cdb_api.h b/lib/cache/cdb_api.h
index 9e8a34d58..f625c3430 100644
--- a/lib/cache/cdb_api.h
+++ b/lib/cache/cdb_api.h
@@ -65,11 +65,15 @@ struct kr_cdb_api {
 	 * \return error code - accepting RW transactions can fail with LMDB.
 	 */
 	int (*commit)(kr_cdb_pt db, struct kr_cdb_stats *stat, bool accept_rw, bool reset_ro);
+	/** Run before a row of operations to ensure they happen in a single RW transaction,
+	 *   at least in case of successes. */
+	int (*txn_open_rw)(kr_cdb_pt db, struct kr_cdb_stats *stat/*unused*/);
 
 	/* Data access */
 
 	int (*read)(kr_cdb_pt db, struct kr_cdb_stats *stat,
 			const knot_db_val_t *key, knot_db_val_t *val, int maxcount);
+	/* TODO: the behavior of write() around transactions is a bit complex. */
 	int (*write)(kr_cdb_pt db, struct kr_cdb_stats *stat, const knot_db_val_t *key,
 			knot_db_val_t *val, int maxcount);
 
diff --git a/lib/cache/cdb_lmdb.c b/lib/cache/cdb_lmdb.c
index 0319b5cbb..6bb5cd82d 100644
--- a/lib/cache/cdb_lmdb.c
+++ b/lib/cache/cdb_lmdb.c
@@ -244,6 +244,13 @@ static int cdb_commit(kr_cdb_pt db, struct kr_cdb_stats *stats, bool accept_rw,
 	return ret;
 }
 
+static int cdb_txn_open_rw(kr_cdb_pt db, struct kr_cdb_stats *stat/*unused*/)
+{
+	struct lmdb_env *env = db2env(db);
+	MDB_txn *txn = NULL;
+	return txn_get(env, &txn, false);
+}
+
 /** Obtain a read-only cursor (and a read-only transaction).
  * TODO: allow RW transaction (for ruledb iterator) */
 static int txn_curs_get(struct lmdb_env *env, MDB_cursor **curs, struct kr_cdb_stats *stats)
@@ -958,7 +965,8 @@ const struct kr_cdb_api *kr_cdb_lmdb(void)
 {
 	static const struct kr_cdb_api api = {
 		"lmdb",
-		cdb_init, cdb_deinit, cdb_count, cdb_clear, cdb_commit,
+		cdb_init, cdb_deinit, cdb_count, cdb_clear,
+		cdb_commit, cdb_txn_open_rw,
 		cdb_readv, cdb_writev, cdb_remove,
 		cdb_match,
 		cdb_read_leq, cdb_read_less,