SIGHUP handlers

Install SIGHUP handlers when node starts, and reinstall them when
consensus started.  In the first case we only can update topology
information, in the later case we can also update block forging.

Author: coot

cardano-node/src/Cardano/Node/Run.hs

@@ -438,6 +438,20 @@ handleSimpleNode blockType runP p2pMode tracers nc onKernel = do
         localRootsVar <- newTVarIO localRoots
         publicRootsVar <- newTVarIO publicRoots
         useLedgerVar   <- newTVarIO (useLedgerAfterSlot nt)
+#ifdef UNIX
+        -- initial `SIGHUP` handler, which only rereads the topology file but
+        -- doesn't update block forging.  The latter is only possible once
+        -- consensus initialised (e.g. reapplied all blocks).
+        _ <- Signals.installHandler
+              Signals.sigHUP
+              (Signals.Catch $ do
+                updateTopologyConfiguration
+                  (startupTracer tracers) nc
+                  localRootsVar publicRootsVar useLedgerVar
+                traceWith (startupTracer tracers) (BlockForgingUpdate NotEffective)
+              )
+              Nothing
+#endif
         void $
           let diffusionArgumentsExtra =
                 mkP2PArguments nc
@@ -448,6 +462,7 @@ handleSimpleNode blockType runP p2pMode tracers nc onKernel = do
           Node.run
             nodeArgs {
                 rnNodeKernelHook = \registry nodeKernel -> do
+                  -- reinstall `SIGHUP` handler
                   installP2PSigHUPHandler (startupTracer tracers) blockType nc nodeKernel
                                           localRootsVar publicRootsVar useLedgerVar
                   rnNodeKernelHook nodeArgs registry nodeKernel
@@ -481,10 +496,23 @@ handleSimpleNode blockType runP p2pMode tracers nc onKernel = do
                            | (NodeAddress (NodeHostIPAddress addr) port) <- ipProducerAddrs
                            ]
                            (length ipProducerAddrs)
+#ifdef UNIX
+        -- initial `SIGHUP` handler; it only warns that neither updating of
+        -- topology is supported nor updating block forging is yet possible.
+        -- It is still useful, without it the node would terminate when
+        -- receiving `SIGHUP`.
+        _ <- Signals.installHandler
+              Signals.sigHUP
+              (Signals.Catch $ do
+                traceWith (startupTracer tracers) NetworkConfigUpdateUnsupported
+                traceWith (startupTracer tracers) (BlockForgingUpdate NotEffective))
+              Nothing
+#endif
         void $
           Node.run
             nodeArgs {
                 rnNodeKernelHook = \registry nodeKernel -> do
+                  -- reinstall `SIGHUP` handler
                   installNonP2PSigHUPHandler (startupTracer tracers) blockType nc nodeKernel
                   rnNodeKernelHook nodeArgs registry nodeKernel
             }

cardano-node/src/Cardano/Node/Startup.hs

@@ -136,6 +136,10 @@ data StartupTrace blk =
 
 data EnabledBlockForging = EnabledBlockForging
                          | DisabledBlockForging
+                         | NotEffective
+                         -- ^ one needs to send `SIGHUP` after consensus
+                         -- initialised itself (especially after replying all
+                         -- blocks).
                          deriving (Eq, Show)
 
 data BasicInfoCommon = BasicInfoCommon {

cardano-node/src/Cardano/Node/Tracing/Tracers/Startup.hs

@@ -493,6 +493,8 @@ ppStartupInfoTrace (BlockForgingUpdate b) =
             "Disabling block forging, to enable it please make the credentials "
           <> "files available again and then re-trigger reconfiguration via SIGHUP "
           <> "signal."
+        NotEffective ->
+             "Changing block forging is not effective until consensus has started. "
 
 ppStartupInfoTrace (BlockForgingUpdateError err) =
   "Block forging reconfiguration error: "