gossipd: put the last_writes array inside struct gossip_store.

diff --git a/gossipd/gossip_store.c b/gossipd/gossip_store.c
index 38366533..93b8d36f 100644
--- a/gossipd/gossip_store.c
+++ b/gossipd/gossip_store.c
@@ -35,6 +35,10 @@ struct gossip_store {
 
 	/* Timestamp of store when we opened it (0 if we created it) */
 	u32 timestamp;
+
+	/* Last writes since previous sync, in case it messes up and
+	 * we need to force it. */
+	const u8 **last_writes;
 };
 
 static void gossip_store_destroy(struct gossip_store *gs)
@@ -414,20 +418,22 @@ struct gossip_store *gossip_store_new(const tal_t *ctx,
 	gs->fd = gossip_store_upgrade(daemon, &gs->len, populated);
 	if (gs->fd < 0)
 		return tal_free(gs);
+	gs->last_writes = tal_arr(gs, const u8 *, 0);
 	tal_add_destructor(gs, gossip_store_destroy);
 	return gs;
 }
 
-void gossip_store_fsync(const struct gossip_store *gs)
+static void gossip_store_fsync(const struct gossip_store *gs)
 {
 	if (fsync(gs->fd) != 0)
 		status_failed(STATUS_FAIL_INTERNAL_ERROR,
 			      "gossmap fsync failed: %s", strerror(errno));
 }
 
-void gossip_store_rewrite_end(struct gossip_store *gs, const u8 **msgs)
+void gossip_store_rewrite_end(struct gossip_store *gs)
 {
 	u64 offset = gs->len;
+	const u8 **msgs = gs->last_writes;
 
 	for (size_t i = 0; i < tal_count(msgs); i++) {
 		/* Don't overwrite version byte */
@@ -447,10 +453,15 @@ void gossip_store_rewrite_end(struct gossip_store *gs, const u8 **msgs)
 	gossip_store_fsync(gs);
 }
 
+void gossip_store_writes_confirmed(struct gossip_store *gs)
+{
+	tal_free(gs->last_writes);
+	gs->last_writes = tal_arr(gs, const u8 *, 0);
+}
+
 u64 gossip_store_add(struct gossip_store *gs,
 		     const u8 *gossip_msg,
-		     u32 timestamp,
-		     const u8 ***msgs)
+		     u32 timestamp)
 {
 	u64 off = gs->len, filelen;
 
@@ -470,7 +481,7 @@ u64 gossip_store_add(struct gossip_store *gs,
 				      filelen, off);
 	}
 
-	if (!append_msg(gs->fd, gossip_msg, timestamp, &gs->len, msgs)) {
+	if (!append_msg(gs->fd, gossip_msg, timestamp, &gs->len, &gs->last_writes)) {
 		status_failed(STATUS_FAIL_INTERNAL_ERROR,
 			      "Failed writing to gossip store: %s",
 			      strerror(errno));
diff --git a/gossipd/gossip_store.h b/gossipd/gossip_store.h
index 5d839169..81e76d7d 100644
--- a/gossipd/gossip_store.h
+++ b/gossipd/gossip_store.h
@@ -44,14 +44,12 @@ void gossip_store_corrupt(void);
  * @gs: gossip store
  * @gossip_msg: the gossip message to insert.
  * @timestamp: the timestamp for filtering of this messsage.
- * @msgs: the option pointer to a u8 *array to append the written msgs to.
  *
  * Returns the offset (after the gossip_hdr).
  */
 u64 gossip_store_add(struct gossip_store *gs,
 		     const u8 *gossip_msg,
-		     u32 timestamp,
-		     const u8 ***msgs);
+		     u32 timestamp);
 
 /**
  * Delete the record at this offset (offset is that of
@@ -107,12 +105,16 @@ void gossip_store_set_timestamp(struct gossip_store *gs, u64 offset, u32 timesta
 /**
  * We've seen (ZFS on Linux) writes not show up in the gossip store.
  * This lets us rewrite the last bytes. */
-void gossip_store_rewrite_end(struct gossip_store *gs, const u8 **msgs);
+void gossip_store_rewrite_end(struct gossip_store *gs);
+
+/**
+ * Once we've checked the contents are good, the last_writes storage can
+ * be reset. */
+void gossip_store_writes_confirmed(struct gossip_store *gs);
 
 /**
  * For debugging.
  */
 u64 gossip_store_len_written(const struct gossip_store *gs);
-void gossip_store_fsync(const struct gossip_store *gs);
 
 #endif /* LIGHTNING_GOSSIPD_GOSSIP_STORE_H */
diff --git a/gossipd/gossmap_manage.c b/gossipd/gossmap_manage.c
index c6cf4862..a9d7f2b8 100644
--- a/gossipd/gossmap_manage.c
+++ b/gossipd/gossmap_manage.c
@@ -65,10 +65,6 @@ struct gossmap_manage {
 	/* gossip map itself (access via gossmap_manage_get_gossmap, so it's fresh!) */
 	struct gossmap *raw_gossmap;
 
-	/* Last writes to gossmap since previous sync, in case it
-	 * messes up and we need to force it. */
-	const u8 **last_writes;
-
 	/* The gossip_store, which writes to the gossip_store file */
 	struct gossip_store *gs;
 
@@ -268,7 +264,7 @@ static void remove_channel(struct gossmap_manage *gm,
 	/* Put in tombstone marker. */
 	gossip_store_add(gm->gs,
 			 towire_gossip_store_delete_chan(tmpctx, scid),
-			 0, &gm->last_writes);
+			 0);
 
 	/* Delete from store */
 	gossip_store_del(gm->gs, chan->cann_off, WIRE_CHANNEL_ANNOUNCEMENT);
@@ -309,7 +305,7 @@ static void remove_channel(struct gossmap_manage *gm,
 			timestamp = gossip_store_get_timestamp(gm->gs, node->nann_off);
 
 			gossip_store_del(gm->gs, node->nann_off, WIRE_NODE_ANNOUNCEMENT);
-			offset = gossip_store_add(gm->gs, nannounce, timestamp, &gm->last_writes);
+			offset = gossip_store_add(gm->gs, nannounce, timestamp);
 		} else {
 			/* Are all remaining channels dying but we weren't?
 			 * Can happen if we removed this channel immediately
@@ -481,7 +477,6 @@ static bool setup_gossmap(struct gossmap_manage *gm,
 		gm->gs = tal_free(gm->gs);
 		return false;
 	}
-	gm->last_writes = tal_arr(gm, const u8 *, 0);
 
 	gossmap_stats(gm->raw_gossmap, &num_live, &num_dead);
 	status_debug("gossip_store: %"PRIu64" live records, %"PRIu64" deleted",
@@ -636,10 +631,9 @@ const char *gossmap_manage_channel_announcement(const tal_t *ctx,
 	 */
 	if (known_amount) {
 		/* Set with timestamp 0 (we will update once we have a channel_update) */
-		gossip_store_add(gm->gs, announce, 0, &gm->last_writes);
+		gossip_store_add(gm->gs, announce, 0);
 		gossip_store_add(gm->gs,
-				 towire_gossip_store_channel_amount(tmpctx, *known_amount), 0,
-				 &gm->last_writes);
+				 towire_gossip_store_channel_amount(tmpctx, *known_amount), 0);
 
 		node_announcements_not_dying(gm, gossmap, pca);
 		tal_free(pca);
@@ -770,10 +764,9 @@ void gossmap_manage_handle_get_txout_reply(struct gossmap_manage *gm, const u8 *
 	}
 
 	/* Set with timestamp 0 (we will update once we have a channel_update) */
-	gossip_store_add(gm->gs, pca->channel_announcement, 0, &gm->last_writes);
+	gossip_store_add(gm->gs, pca->channel_announcement, 0);
 	gossip_store_add(gm->gs,
-			 towire_gossip_store_channel_amount(tmpctx, sat), 0,
-			 &gm->last_writes);
+			 towire_gossip_store_channel_amount(tmpctx, sat), 0);
 
 	/* If we looking specifically for this, we no longer are. */
 	remove_unknown_scid(gm->daemon->seeker, &scid, true);
@@ -875,7 +868,7 @@ static const char *process_channel_update(const tal_t *ctx,
 	}
 
 	/* OK, apply the new one */
-	offset = gossip_store_add(gm->gs, update, timestamp, &gm->last_writes);
+	offset = gossip_store_add(gm->gs, update, timestamp);
 
 	/* If channel is dying, make sure update is also marked dying! */
 	if (gossmap_chan_is_dying(gossmap, chan)) {
@@ -1054,7 +1047,7 @@ static void process_node_announcement(struct gossmap_manage *gm,
 	}
 
 	/* OK, apply the new one */
-	offset = gossip_store_add(gm->gs, nannounce, timestamp, &gm->last_writes);
+	offset = gossip_store_add(gm->gs, nannounce, timestamp);
 	/* If all channels are dying, make sure this is marked too. */
 	if (all_node_channels_dying(gossmap, node, NULL)) {
 		gossip_store_set_flag(gm->gs, offset,
@@ -1381,7 +1374,7 @@ void gossmap_manage_channel_spent(struct gossmap_manage *gm,
 
 	/* Save to gossip_store in case we restart */
 	msg = towire_gossip_store_chan_dying(tmpctx, cd.scid, cd.deadline);
-	cd.gossmap_offset = gossip_store_add(gm->gs, msg, 0, &gm->last_writes);
+	cd.gossmap_offset = gossip_store_add(gm->gs, msg, 0);
 	tal_arr_expand(&gm->dying_channels, cd);
 
 	/* Mark it dying, so we don't gossip it */
@@ -1485,7 +1478,7 @@ struct gossmap *gossmap_manage_get_gossmap(struct gossmap_manage *gm)
 		gossmap_disable_mmap(gm->raw_gossmap);
 
 		/* Try rewriting the last few records, syncing. */
-		gossip_store_rewrite_end(gm->gs, gm->last_writes);
+		gossip_store_rewrite_end(gm->gs);
 		gossmap_refresh(gm->raw_gossmap);
 
 		map_used = gossmap_lengths(gm->raw_gossmap, &map_size);
@@ -1497,8 +1490,7 @@ struct gossmap *gossmap_manage_get_gossmap(struct gossmap_manage *gm)
 	}
 
 	/* Free up last_writes, since we've seen it on disk */
-	tal_free(gm->last_writes);
-	gm->last_writes = tal_arr(gm, const u8 *, 0);
+	gossip_store_writes_confirmed(gm->gs);
 	return gm->raw_gossmap;
 }