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diff --git a/src/knot/journal/journal_basic.h b/src/knot/journal/journal_basic.h
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+/*  Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "knot/conf/conf.h"
+#include "knot/journal/knot_lmdb.h"
+#include "knot/updates/changesets.h"
+#include "libknot/dname.h"
+
+typedef struct {
+	knot_lmdb_db_t *db;
+	const knot_dname_t *zone;
+	void *conf; // needed only for journal write operations
+} zone_journal_t;
+
+#define JOURNAL_CHUNK_MAX (70 * 1024) // must be at least 64k + 6B
+#define JOURNAL_CHUNK_THRESH (15 * 1024)
+#define JOURNAL_HEADER_SIZE (32)
+
+/*! \brief Convert journal_mode to LMDB environment flags. */
+inline static unsigned journal_env_flags(int journal_mode, bool readonly)
+{
+	return (journal_mode == JOURNAL_MODE_ASYNC ? (MDB_WRITEMAP | MDB_MAPASYNC) : 0) |
+	       (readonly ? MDB_RDONLY : 0);
+}
+
+/*!
+ * \brief Create a database key prefix to search for a changeset.
+ *
+ * \param zone_in_journal   True if searching for zone-in-journal special changeset.
+ * \param serial            Serial-from of the changeset to be searched for. Ignored if 'zone_in_journal'.
+ * \param zone              Name of the zone.
+ *
+ * \return DB key. 'mv_data' shall be freed later. 'mv_data' is NULL on failure.
+ */
+MDB_val journal_changeset_id_to_key(bool zone_in_journal, uint32_t serial, const knot_dname_t *zone);
+
+/*!
+ * \brief Create a database key for changeset chunk.
+ *
+ * \param apex       Zone apex owner name.
+ * \param ch_from    Serial "from" of the stored changeset.
+ * \param zij        Zone-in-journal is stored.
+ * \param chunk_id   Ordinal number of this changeset's chunk.
+ *
+ * \return DB key. 'mv_data' shall be freed later. 'mv_data' is NULL on failure.
+ */
+MDB_val journal_make_chunk_key(const knot_dname_t *apex, uint32_t ch_from, bool zij, uint32_t chunk_id);
+
+/*!
+ * \brief Return a key prefix to operate with all zone-related records.
+ */
+MDB_val journal_zone_prefix(const knot_dname_t *zone);
+
+/*!
+ * \brief Delete all zone-related records from journal with open read-write txn.
+ */
+void journal_del_zone(knot_lmdb_txn_t *txn, const knot_dname_t *zone);
+
+/*!
+ * \brief Initialise chunk header.
+ *
+ * \param chunk   Pointer to the changeset chunk. It must be at least JOURNAL_HEADER_SIZE, perhaps more.
+ * \param ch      Serial-to of the changeset being serialized.
+ */
+void journal_make_header(void *chunk, uint32_t ch_serial_to);
+
+/*!
+ * \brief Obtain serial-to of the serialized changeset.
+ *
+ * \param chunk   Any chunk of a serialized changeset.
+ *
+ * \return The changeset's serial-to.
+ */
+uint32_t journal_next_serial(const MDB_val *chunk);
+
+/*!
+ * \brief Obtain serial-to of a changeset stored in journal.
+ *
+ * \param txn         Journal DB transaction.
+ * \param zij         True if changeset in question is zone-in-journal.
+ * \param serial      Serial-from of the changeset in question.
+ * \param zone        Zone name.
+ * \param serial_to   Output: serial-to of the changeset in question.
+ *
+ * \return True if the changeset exists in the journal.
+ */
+bool journal_serial_to(knot_lmdb_txn_t *txn, bool zij, uint32_t serial,
+                       const knot_dname_t *zone, uint32_t *serial_to);
+
+/*! \brief Return true if the changeset in question exists in the journal. */
+inline static bool journal_contains(knot_lmdb_txn_t *txn, bool zone, uint32_t serial, const knot_dname_t *zone_name)
+{
+	return journal_serial_to(txn, zone, serial, zone_name, NULL);
+}
+
+/*! \brief Return true if the journal may be flushed according to conf. */
+bool journal_allow_flush(zone_journal_t j);
+
+/*! \brief Return configured maximal per-zone usage of journal DB. */
+size_t journal_conf_max_usage(zone_journal_t j);
+
+/*! \brief Return configured maximal depth of journal. */
+size_t journal_conf_max_changesets(zone_journal_t j);