lightningd: speed mapping from coinmoves table to channel for listcoinmoves.

diff --git a/lightningd/channel.c b/lightningd/channel.c
index d69865b2..354249a4 100644
--- a/lightningd/channel.c
+++ b/lightningd/channel.c
@@ -312,6 +312,20 @@ void channel_add_old_scid(struct channel *channel,
 	chanmap_add(channel->peer->ld, channel, old_scid);
 }
 
+static void remove_from_dbid_map(struct channel *channel)
+{
+	if (!channel_dbid_map_del(channel->peer->ld->channels_by_dbid, channel))
+		abort();
+}
+
+void add_channel_to_dbid_map(struct lightningd *ld,
+			     struct channel *channel)
+{
+	assert(channel->dbid != 0);
+	channel_dbid_map_add(ld->channels_by_dbid, channel);
+	tal_add_destructor(channel, remove_from_dbid_map);
+}
+
 struct channel *new_unsaved_channel(struct peer *peer,
 				    u32 feerate_base,
 				    u32 feerate_ppm)
@@ -698,6 +712,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 	channel->rr_number = peer->ld->rr_counter++;
 	tal_add_destructor(channel, destroy_channel);
 
+	add_channel_to_dbid_map(peer->ld, channel);
 	list_head_init(&channel->inflights);
 
 	channel->closer = closer;
@@ -842,20 +857,7 @@ struct channel *any_channel_by_scid(struct lightningd *ld,
 
 struct channel *channel_by_dbid(struct lightningd *ld, const u64 dbid)
 {
-	struct peer *p;
-	struct channel *chan;
-	struct peer_node_id_map_iter it;
-
-	/* FIXME: Support lookup by id directly! */
-	for (p = peer_node_id_map_first(ld->peers, &it);
-	     p;
-	     p = peer_node_id_map_next(ld->peers, &it)) {
-		list_for_each(&p->channels, chan, list) {
-			if (chan->dbid == dbid)
-				return chan;
-		}
-	}
-	return NULL;
+	return channel_dbid_map_get(ld->channels_by_dbid, dbid);
 }
 
 struct channel *channel_by_cid(struct lightningd *ld,
diff --git a/lightningd/channel.h b/lightningd/channel.h
index 0e4959e8..af2f18a5 100644
--- a/lightningd/channel.h
+++ b/lightningd/channel.h
@@ -784,6 +784,27 @@ static inline bool channel_state_open_uncommitted(enum channel_state state)
 	abort();
 }
 
+static inline size_t channel_dbid_hash(u64 dbid)
+{
+	return siphash24(siphash_seed(), &dbid, sizeof(dbid));
+}
+
+static u64 channel_dbid(const struct channel *channel)
+{
+	assert(channel->dbid);
+	return channel->dbid;
+}
+
+static bool channel_dbid_eq(const struct channel *channel, u64 dbid)
+{
+	return channel->dbid == dbid;
+}
+/* Defines struct channel_dbid_map */
+HTABLE_DEFINE_NODUPS_TYPE(struct channel,
+			  channel_dbid, channel_dbid_hash, channel_dbid_eq,
+			  channel_dbid_map);
+
+void add_channel_to_dbid_map(struct lightningd *ld, struct channel *channel);
 
 void channel_set_owner(struct channel *channel, struct subd *owner);
 
diff --git a/lightningd/dual_open_control.c b/lightningd/dual_open_control.c
index fe995d3d..3ad5cfb1 100644
--- a/lightningd/dual_open_control.c
+++ b/lightningd/dual_open_control.c
@@ -1446,6 +1446,7 @@ wallet_commit_channel(struct lightningd *ld,
 	channel_info->old_remote_per_commit = channel_info->remote_per_commit;
 
 	/* Promote the unsaved_dbid to the dbid */
+	assert(channel->dbid == 0);
 	assert(channel->unsaved_dbid != 0);
 	channel->dbid = channel->unsaved_dbid;
 	channel->unsaved_dbid = 0;
@@ -1524,6 +1525,9 @@ wallet_commit_channel(struct lightningd *ld,
 	/* Now we finally put it in the database. */
 	wallet_channel_insert(ld->wallet, channel);
 
+	/* So we can find it by the newly-assigned dbid */
+	add_channel_to_dbid_map(ld, channel);
+
 	/* Open attempt to channel's inflights */
 	inflight = new_inflight(channel,
 				NULL,
diff --git a/lightningd/lightningd.c b/lightningd/lightningd.c
index d76d5b60..452cee38 100644
--- a/lightningd/lightningd.c
+++ b/lightningd/lightningd.c
@@ -213,6 +213,10 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	ld->channels_by_scid = tal(ld, struct channel_scid_map);
 	channel_scid_map_init(ld->channels_by_scid);
 
+	/*~ Coin movements in db are indexed by the channel dbid. */
+	ld->channels_by_dbid = tal(ld, struct channel_dbid_map);
+	channel_dbid_map_init(ld->channels_by_dbid);
+
 	/*~ For multi-part payments, we need to keep some incoming payments
 	 * in limbo until we get all the parts, or we time them out. */
 	ld->htlc_sets = tal(ld, struct htlc_set_map);
diff --git a/lightningd/lightningd.h b/lightningd/lightningd.h
index 44a76e18..306b8c29 100644
--- a/lightningd/lightningd.h
+++ b/lightningd/lightningd.h
@@ -218,6 +218,9 @@ struct lightningd {
 	/* Here are all our channels and their aliases */
 	struct channel_scid_map *channels_by_scid;
 
+	/* Open channels by dbid */
+	struct channel_dbid_map *channels_by_dbid;
+
 	/* Outstanding connect commands. */
 	struct list_head connects;
 
diff --git a/wallet/test/run-wallet.c b/wallet/test/run-wallet.c
index 13aa9461..84ac059d 100644
--- a/wallet/test/run-wallet.c
+++ b/wallet/test/run-wallet.c
@@ -1358,6 +1358,8 @@ static struct wallet *create_test_wallet(struct lightningd *ld, const tal_t *ctx
 	/* Create fresh channels map */
 	ld->channels_by_scid = tal(ld, struct channel_scid_map);
 	channel_scid_map_init(ld->channels_by_scid);
+	ld->channels_by_dbid = tal(ld, struct channel_dbid_map);
+	channel_dbid_map_init(ld->channels_by_dbid);
 	return w;
 }
 
@@ -2088,8 +2090,10 @@ static bool test_channel_inflight_crud(struct lightningd *ld, const tal_t *ctx)
 	/* do inflights get correctly added to the channel? */
 	wallet_inflight_add(w, inflight);
 
-	/* Hack to remove scids from htable so we don't clash! */
+	/* Hack to remove scid & dbid from htables so we don't clash! */
 	chanmap_remove(ld, chan, *chan->alias[LOCAL]);
+	remove_from_dbid_map(chan);
+	tal_del_destructor(chan, remove_from_dbid_map);
 
 	/* do inflights get correctly loaded from the database? */
 	CHECK_MSG(c2 = wallet_channel_load(w, chan->dbid),
@@ -2385,6 +2389,8 @@ int main(int argc, const char *argv[])
 	list_head_init(&ld->wait_commands);
 	ld->closed_channels = tal(ld, struct closed_channel_map);
 	closed_channel_map_init(ld->closed_channels);
+	ld->channels_by_dbid = tal(ld, struct channel_dbid_map);
+	channel_dbid_map_init(ld->channels_by_dbid);
 
 	/* We do a runtime test here, so we still check compile! */
 	if (HAVE_SQLITE3) {