From c3c73fcbe7dfac10abaf51bdc1d57858d396b85b Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sun, 19 Mar 2023 12:41:45 -0700
Subject: [PATCH] ircd: Promote slave-mode to a non-maintenance mode allowing
 listeners.

---
 construct/construct.cc     |  2 +-
 include/ircd/db/database.h |  1 -
 include/ircd/ircd.h        |  5 ++--
 ircd/db_database.cc        | 13 +---------
 ircd/ircd.cc               | 20 +++++++++++++++
 modules/m_listen.cc        | 51 ++++++++++++++++++++++++--------------
 6 files changed, 58 insertions(+), 34 deletions(-)

diff --git a/construct/construct.cc b/construct/construct.cc
index 77ae2ea56..e19b114d6 100644
--- a/construct/construct.cc
+++ b/construct/construct.cc
@@ -571,7 +571,7 @@ applyargs()
 
 	if(slave)
 	{
-		ircd::db::open_slave.set("true");
+		ircd::slave.set("true");
 		read_only = true; // slave implies read_only
 	}
 
diff --git a/include/ircd/db/database.h b/include/ircd/db/database.h
index a821c0d50..08fb5c9e7 100644
--- a/include/ircd/db/database.h
+++ b/include/ircd/db/database.h
@@ -18,7 +18,6 @@ namespace ircd::db
 	// Broad conf items
 	extern conf::item<std::string> open_recover;
 	extern conf::item<bool> open_repair;
-	extern conf::item<bool> open_slave;
 	extern conf::item<bool> auto_compact;
 	extern conf::item<bool> auto_deletion;
 	extern conf::item<bool> open_stats;
diff --git a/include/ircd/ircd.h b/include/ircd/ircd.h
index 50fbb2d4a..5e423432f 100644
--- a/include/ircd/ircd.h
+++ b/include/ircd/ircd.h
@@ -129,9 +129,10 @@ namespace ircd
 
 	// Operating Mode Selectors
 	extern conf::item<bool> debugmode;
-	extern conf::item<bool> maintenance;
 	extern conf::item<bool> soft_assert;
-	extern conf::item<bool> read_only;       // implies write_avoid
+	extern conf::item<bool> maintenance;
+	extern conf::item<bool> slave;
+	extern conf::item<bool> read_only;
 	extern conf::item<bool> defaults;
 }
 
diff --git a/ircd/db_database.cc b/ircd/db_database.cc
index 266fafb69..8e0a395c6 100644
--- a/ircd/db_database.cc
+++ b/ircd/db_database.cc
@@ -81,17 +81,6 @@ ircd::db::auto_deletion
 	{ "persist",  false                   },
 };
 
-/// Conf item dictates whether databases will be opened in slave mode; this
-/// is a recent feature of RocksDB which may not be available. It allows two
-/// instances of a database, so long as only one is not opened as a slave.
-decltype(ircd::db::open_slave)
-ircd::db::open_slave
-{
-	{ "name",     "ircd.db.open.slave" },
-	{ "default",  false                },
-	{ "persist",  false                },
-};
-
 /// Gather statistics about files on open to inform the compaction algorithm.
 /// This can be disabled to prevent touching a lot of files on open, but it's
 /// unclear when/if that information will be gathered to ever inform compactor.
@@ -940,7 +929,7 @@ try
 }
 ,slave
 {
-	db::open_slave
+	ircd::slave
 }
 ,read_only
 {
diff --git a/ircd/ircd.cc b/ircd/ircd.cc
index 482383df4..f2a75fdc2 100644
--- a/ircd/ircd.cc
+++ b/ircd/ircd.cc
@@ -107,6 +107,22 @@ ircd::maintenance
 	}
 };
 
+/// Conf item dictates whether databases will be opened in slave mode; this
+/// is a recent feature of RocksDB which may not be available. It allows
+/// multiple processes to open the same database in a single-writer multiple
+/// reader configuration.
+///
+/// Originally this was intended as a maintenance mode to explore another live
+/// running server's database. However it now allows listeners which can serve
+/// as load-balanced mirrors and caches over a database shared at the fs level
+/// locally or with nfs/ceph/intermezzo etc.
+decltype(ircd::slave)
+ircd::slave
+{
+	{ "name",     "ircd.slave"   },
+	{ "default",  false          },
+	{ "persist",  false          },
+};
 
 /// Coarse mode declaration for read-only behavior. All subsystems and feature
 /// modules respect this indicator by preventing any writes and persistence
@@ -125,6 +141,10 @@ ircd::read_only
 		if(!read_only)
 			return;
 
+		// Not implict maintenance mode when slave mode is set.
+		if(slave)
+			return;
+
 		maintenance.set("true");
 	}
 };
diff --git a/modules/m_listen.cc b/modules/m_listen.cc
index f2f935ae0..2e546c6e8 100644
--- a/modules/m_listen.cc
+++ b/modules/m_listen.cc
@@ -63,6 +63,11 @@ on_load()
 
 	init_conf_listeners();
 	init_room_listeners();
+	if(listeners.empty())
+		log::warning
+		{
+			"No listening sockets configured; can't hear anyone."
+		};
 }
 
 void
@@ -145,7 +150,7 @@ init_conf_listeners()
 			{
 				"Listener '%s' configured for %s:%s by environment",
 				p.first,
-				p.second["host"],
+				unquote(p.second["host"]),
 				p.second["port"],
 			};
 }
@@ -167,12 +172,6 @@ init_room_listeners()
 	{
 		load_listener(event);
 	});
-
-	if(listeners.empty())
-		log::warning
-		{
-			"No listening sockets configured; can't hear anyone."
-		};
 }
 
 //
@@ -265,19 +264,35 @@ load_listener(const m::event &event)
 		json::get<"content"_>(event)
 	};
 
-	if(!load_listener(name, opts))
-		return false;
-
-	log::notice
+	if(ircd::slave)
 	{
-		"Listener '%s' configured for %s:%s by %s",
-		name,
-		opts["host"],
-		opts["port"],
-		string_view{event.event_id},
-	};
+		log::warning
+		{
+			"Listener '%s' configured for %s:%s by %s ignored in slave mode.",
+			name,
+			unquote(opts["host"]),
+			opts["port"],
+			string_view{event.event_id},
+		};
 
-	return true;
+		return false;
+	}
+
+	if(load_listener(name, opts))
+	{
+		log::notice
+		{
+			"Listener '%s' configured for %s:%s by %s",
+			name,
+			unquote(opts["host"]),
+			opts["port"],
+			string_view{event.event_id},
+		};
+
+		return true;
+	}
+
+	return false;
 }
 
 ctx::context