monitors/alsa: remove vm.node.defaults and use match rules instead

The vm.node.defaults logic which was inherited from p-m-s is not really
good because it seems like different VM hardware requires different
values for the defaults. Also, passthrough USB hardware should not
inerhit these values, they just cause trouble.

Instead, we can use rules to match the vm.type and specific device
properties to set a more informed period & headroom.

For now, I am also decreasing the default headroom down to 2048, which
works for me and perhaps it's a good default. We can always add more
rules here and fine-tune per vm type and virtual hardware.

See !394, #316, #348, #507, #162, pipewire#3452

src/config/wireplumber.conf.d/alsa-vm.conf

@@ -0,0 +1,23 @@
+# ALSA node property overrides for virtual machine hardware
+
+monitor.alsa.rules = [
+  # Generic PCI cards on any VM type
+  {
+    matches = [
+      {
+        node.name = "~alsa_input.pci.*"
+        vm.type = "~.*"
+      }
+      {
+        node.name = "~alsa_output.pci.*"
+        vm.type = "~.*"
+      }
+    ]
+    actions = {
+      update-props = {
+        api.alsa.period-size   = 1024
+        api.alsa.headroom      = 2048
+      }
+    }
+  }
+]

src/config/wireplumber.conf.d/alsa.conf

@@ -22,14 +22,6 @@ monitor.alsa.midi.node-properties = {
   # api.alsa.disable-longname = false
 }
 
-monitor.alsa.vm.node.defaults = {
-  ## These properties override node defaults when running in a virtual machine.
-  ## The rules below still override those.
-
-  api.alsa.period-size = 1024
-  api.alsa.headroom = 8192
-}
-
 monitor.alsa.rules = [
   ## The list of monitor rules
 

src/scripts/monitors/alsa.lua

@@ -12,7 +12,6 @@ defaults = {}
 defaults.reserve_priority = -20
 defaults.reserve_application_name = "WirePlumber"
 defaults.properties = Json.Object {}
-defaults.vm_node_defaults = Json.Object {}
 
 config = {}
 config.reserve_device = Core.test_feature ("monitor.alsa.reserve-device")
@@ -22,8 +21,6 @@ config.reserve_application_name = Conf.get_value_string ("wireplumber.settings",
     "monitor.alsa.reserve-application-name", defaults.reserve_application_name)
 config.properties = Conf.get_section (
     "monitor.alsa.properties", defaults.properties):parse ()
-config.vm_node_defaults = Conf.get_section (
-    "monitor.alsa.vm.node.defaults", defaults.vm_node_defaults):parse ()
 
 -- unique device/node name tables
 device_names_table = nil
@@ -155,12 +152,10 @@ function createNode(parent, id, obj_type, factory, properties)
     end
   end
 
-  -- apply VM overrides
-  if nonempty(Core.get_vm_type()) and
-      type(config.vm_node_defaults) == "table" then
-    for k, v in pairs(config.vm_node_defaults) do
-      properties[k] = v
-    end
+  -- add vm.type for rule matching purposes
+  local vm_type = Core.get_vm_type()
+  if nonempty(vm_type) then
+    properties["vm.type"] = vm_type
   end
 
   -- apply properties from rules defined in JSON .conf file