Update

pipewire/.config/wireplumber/scripts/monitors/alsa-midi.lua

@@ -0,0 +1,74 @@
+-- WirePlumber
+--
+-- Copyright © 2021 Collabora Ltd.
+--    @author Julian Bouzas <julian.bouzas@collabora.com>
+--
+-- SPDX-License-Identifier: MIT
+
+cutils = require ("common-utils")
+log = Log.open_topic ("s-monitors")
+
+defaults = {}
+defaults.node_properties = {  -- Midi bridge node properties
+  ["factory.name"] = "api.alsa.seq.bridge",
+
+  -- Name set for the node with ALSA MIDI ports
+  ["node.name"] = "Midi-Bridge",
+
+  -- Set priorities so that it can be used as a fallback driver (see pipewire#3562)
+  ["priority.session"] = "100",
+  ["priority.driver"] = "1",
+}
+
+config = {}
+config.monitoring = Core.test_feature ("monitor.alsa-midi.monitoring")
+config.node_properties = Conf.get_section_as_properties (
+    "monitor.alsa-midi.properties", defaults.node_properties)
+
+SND_PATH = "/dev/snd"
+SEQ_NAME = "seq"
+SND_SEQ_PATH = SND_PATH .. "/" .. SEQ_NAME
+
+midi_node = nil
+fm_plugin = nil
+
+function CreateMidiNode ()
+  -- create the midi node
+  local node = Node("spa-node-factory", config.node_properties)
+  node:activate(Feature.Proxy.BOUND, function (n)
+    log:info ("activated Midi bridge")
+  end)
+
+  return node;
+end
+
+if GLib.access (SND_SEQ_PATH, "rw") then
+  midi_node = CreateMidiNode ()
+elseif config.monitoring then
+  fm_plugin = Plugin.find("file-monitor-api")
+end
+
+-- Only monitor the MIDI device if file does not exist and plugin API is loaded
+if midi_node == nil and fm_plugin ~= nil then
+  -- listen for changed events
+  fm_plugin:connect ("changed", function (o, file, old, evtype)
+    -- files attributes changed
+    if evtype == "attribute-changed" then
+      if file ~= SND_SEQ_PATH then
+        return
+      end
+      if midi_node == nil and GLib.access (SND_SEQ_PATH, "rw") then
+        midi_node = CreateMidiNode ()
+        fm_plugin:call ("remove-watch", SND_PATH)
+      end
+    end
+
+    -- directory is going to be unmounted
+    if evtype == "pre-unmount" then
+      fm_plugin:call ("remove-watch", SND_PATH)
+    end
+  end)
+
+  -- add watch
+  fm_plugin:call ("add-watch", SND_PATH, "m")
+end