monitor-utils: Rework camera deduplication code

The previous code made some invalid assumptions and was rather
complicated. Rework and simplify it.

The approach work as follows:
1. Once a new device gets registered, store its data in a list of pending
   devices.
2. Start a timer. On timeout, we check all pending devices and depulicate
   according to our heuristic. The timer gets reset whenever a device is
   added in order to avoid race conditions.
3. On timeout, add the pending devices to categories. For now: UVC cameras
   from the V4L2 plugin, libcamera cameras and other cameras from the V4L2
   plugin.
4. Then process the different categories in order of preference and store
   their V4L2 device IDs in a list for each plugin.
5. Before creating a camera, check that the V4L2 device(s) it uses are not
   yet used by a already existing camera from the other plugin.

While on it, drop support for Pipewire versions that don't report V4L2
device IDs at all.

Closes https://gitlab.freedesktop.org/pipewire/wireplumber/-/issues/689
Closes https://gitlab.freedesktop.org/pipewire/wireplumber/-/issues/708

src/scripts/lib/monitor-utils.lua

@@ -10,7 +10,8 @@
 log = Log.open_topic ("s-monitors-utils")
 
 local mutils = {
-  cam_data = {}
+  cam_data = {},
+  cam_source = nil
 }
 
 -- finds out if any of the managed objects(nodes of a device or devices of
@@ -25,173 +26,126 @@ function mutils.find_duplicate (parent, id, property, value)
   return false
 end
 
-function get_cam_data(self, dev_id)
-  if not self.cam_data[dev_id] then
-    self.cam_data[dev_id] = {}
-    self.cam_data[dev_id]["libcamera"] = {}
-    self.cam_data[dev_id]["v4l2"] = {}
-  end
-  return self.cam_data[dev_id]
-end
+function create_cam_node(cam_data)
+  local api = cam_data.properties["device.api"]
 
-function parse_devids_get_cam_data(self, devids)
-  local dev_ids_json = Json.Raw(devids)
-  local dev_ids_table = {}
-
-  if dev_ids_json:is_array() then
-    dev_ids_table = dev_ids_json:parse()
-  else
-    -- to maintain the backward compatibility with earlier pipewire versions.
-    for dev_id_str in devids:gmatch("%S+") do
-      local dev_id = tonumber(dev_id_str)
-      if dev_id then
-        table.insert(dev_ids_table, dev_id)
-      end
-    end
-  end
-
-  local dev_num = nil
-  -- `device.devids` is a json array of device numbers
-  for _, dev_id_str in ipairs(dev_ids_table) do
-    local dev_id = tonumber(dev_id_str)
-    if not dev_id then
-      log:notice ("invalid device number")
-      return
-    end
-
-    log:debug ("Working on device " .. dev_id)
-    local dev_cam_data = get_cam_data (self, dev_id)
-    if not dev_num then
-      dev_num = dev_id
-      if #dev_ids_table > 1 then
-        -- libcam node can some times use more tha one V4L2 devices, in this
-        -- case, return the first device id and mark rest of the them as peers
-        -- to the first one.
-        log:debug ("Device " .. dev_id .. " uses multi V4L2 devices")
-        dev_cam_data.uses_multi_v4l2_devices = true
-      end
-    else
-      log:debug ("Device " .. dev_id .. " is peer to " .. dev_num)
-      dev_cam_data.peer_id = dev_num
-    end
-  end
-
-  if dev_num then
-    return self.cam_data[dev_num], dev_num
-  end
-end
-
-function mutils.clear_cam_data (self, dev_num)
-  local dev_cam_data = self.cam_data[dev_num]
-  if not dev_cam_data then
-    return
-  end
-
-  if dev_cam_data.uses_multi_v4l2_devices then
-    for dev_id, cam_data_ in pairs(self.cam_data) do
-      if cam_data_.peer_id == dev_num then
-        log:debug("clear " .. dev_id .. " it is peer to " .. dev_num)
-        self.cam_data[dev_id] = nil
-      end
-    end
-  end
-
-  self.cam_data[dev_num] = nil
-end
-
-function mutils.create_cam_node(self, dev_num)
-  local api = nil
-  local cam_data = get_cam_data (self, dev_num)
-
-  if cam_data["v4l2"].enum_status and cam_data["libcamera"].enum_status then
-    if cam_data.uses_multi_v4l2_devices then
-      api = "libcamera"
-    elseif cam_data.peer_id ~= nil then
-      -- no need to create node for peer
-      log:notice ("timer expired for peer device " .. dev_num)
-      return
-    elseif cam_data.is_device_uvc then
-      api = "v4l2"
-    else
-      api = "libcamera"
-    end
-  else
-    api = cam_data["v4l2"].enum_status and "v4l2" or "libcamera"
-  end
-
-  log:info (string.format ("create \"%s\" node for device:%s", api,
-    cam_data.dev_path))
+  log:info ("create " .. api .. " node for device: " .. cam_data.obj_path)
 
   source = source or Plugin.find ("standard-event-source")
   local e = source:call ("create-event", "create-" .. api .. "-device-node",
-    cam_data[api].parent, nil)
-  e:set_data ("factory", cam_data[api].factory)
-  e:set_data ("node-properties", cam_data[api].properties)
-  e:set_data ("node-sub-id", cam_data[api].id)
+    cam_data.parent, nil)
+  e:set_data ("factory", cam_data.factory)
+  e:set_data ("node-properties", cam_data.properties)
+  e:set_data ("node-sub-id", cam_data.id)
 
   EventDispatcher.push_event (e)
-
-  self:clear_cam_data (dev_num)
 end
 
+function table_contains(table, element)
+  for _, value in pairs(table) do
+    if value == element then
+      return true
+    end
+  end
+  return false
+end
+
+function mutils.create_cam_nodes(self)
+  log:debug("create_cam_nodes for " .. #self.cam_data .. " devices")
+
+  local libcamera_cameras = {}
+  local v4l2_uvc_cameras = {}
+  local v4l2_other_cameras = {}
+
+  for _, data in ipairs(self.cam_data) do
+    local api = data.properties["device.api"]
+
+    local dev_ids = data.properties["device.devids"]
+    local dev_ids_json = Json.Raw(dev_ids)
+
+    if dev_ids_json:is_array() then
+      data.dev_ids = dev_ids_json:parse()
+    else
+      data.dev_ids = {}
+      -- to maintain the backward compatibility with earlier pipewire versions.
+      for dev_id_str in dev_ids:gmatch("%S+") do
+        local dev_id = tonumber(dev_id_str)
+        if dev_id then
+          table.insert(data.dev_ids, dev_id)
+        end
+      end
+    end
+
+    if api == 'libcamera' then
+      table.insert(libcamera_cameras, data)
+    elseif api == 'v4l2' then
+      if data.properties["api.v4l2.cap.driver"] == "uvcvideo" then
+        table.insert(v4l2_uvc_cameras, data)
+      else
+        table.insert(v4l2_other_cameras, data)
+      end
+    else
+      log:warning("Got camera with unknown API, ignoring")
+    end
+  end
+
+  local device_ids_libcamera = {}
+  local device_ids_v4l2 = {}
+
+  for _, data in ipairs(v4l2_uvc_cameras) do
+    create_cam_node (data)
+    table.insert(device_ids_v4l2, data.dev_ids[1])
+  end
+
+  for _, data in ipairs(libcamera_cameras) do
+    if table_contains(device_ids_v4l2, data.dev_ids[1]) then
+      log:debug ("skipping device " .. data.obj_path)
+    else
+      create_cam_node (data)
+      table.insert(device_ids_libcamera, data.dev_ids[1])
+    end
+  end
+
+  for _, data in ipairs(v4l2_other_cameras) do
+    if table_contains(device_ids_libcamera, data.dev_ids[1]) then
+      log:debug ("skipping device " .. data.obj_path)
+    else
+      create_cam_node (data)
+    end
+  end
+
+  self.cam_data = {}
+end
+
+
 -- arbitrates between v4l2 and libcamera on who gets to create the device node
 -- for a device, logic is based on the device number of the device given by both
 -- the parties.
 function mutils.register_cam_node (self, parent, id, factory, properties)
+  local obj_path = properties["object.path"]
   local api = properties["device.api"]
   local dev_ids = properties["device.devids"]
-  log:debug(api .. " reported " .. dev_ids)
-
-  local cam_data, dev_num = parse_devids_get_cam_data(self, dev_ids)
-
-  if not cam_data then
-    log:notice (string.format ("device numbers invalid for %s device:%s",
-      api, properties["device.name"]))
-    return false
-  end
-
-  -- only v4l2 can give this info
-  if properties["api.v4l2.cap.driver"] == "uvcvideo" then
-    log:debug ("Device " .. dev_num .. " is a UVC device")
-    cam_data.is_device_uvc = true
-  end
-
-  -- only v4l2 can give this info
-  if properties["api.v4l2.path"] then
-    cam_data.dev_path = properties["api.v4l2.path"]
-  end
-
-  local cam_api_data = cam_data[api]
-  cam_api_data.enum_status = true
+  log:debug(api .. " reported device " .. obj_path .. " with device ids " .. dev_ids)
 
   -- cache info, it comes handy when creating node
-  cam_api_data.parent = parent
-  cam_api_data.id = id
-  cam_api_data.name = properties["device.name"]
-  cam_api_data.factory = factory
-  cam_api_data.properties = properties
+  local cam_data = {}
+  cam_data.id = id
+  cam_data.parent = parent
+  cam_data.obj_path = obj_path
+  cam_data.factory = factory
+  cam_data.properties = properties
 
-  local other_api = api == "v4l2" and "libcamera" or "v4l2"
-  if cam_api_data.enum_status and not cam_data[other_api].enum_status then
-    log:trace (string.format ("\"%s\" armed a timer for %d", api, dev_num))
-    cam_data.source = Core.timeout_add (
-      Settings.get_int ("monitor.camera-discovery-timeout"), function()
-        log:trace (string.format ("\"%s\" armed timer expired for %d", api, dev_num))
-        self:create_cam_node (dev_num)
-        cam_data.source = nil
-      end)
-  elseif cam_data.source then
-    log:trace (string.format ("\"%s\" disarmed timer for %d", api, dev_num))
-    cam_data.source:destroy ()
-    cam_data.source = nil
-    self:create_cam_node (dev_num)
-  else
-    log:notice (string.format ("\"%s\" calling after timer expiry for %d:%s%s",
-      api, dev_num, cam_data.dev_path,
-      (cam_data.is_device_uvc and "(uvc)" or "")))
+  table.insert(self.cam_data, cam_data)
+
+  if self.cam_source then
+    self.cam_source:destroy ()
   end
 
-  return true
+  self.cam_source = Core.timeout_add (
+    Settings.get_int ("monitor.camera-discovery-timeout"), function()
+      self:create_cam_nodes ()
+      self.cam_source = nil
+  end)
 end
 
 return mutils

src/scripts/monitors/libcamera/create-device.lua

@@ -14,17 +14,7 @@ config = {}
 config.rules = Conf.get_section_as_json ("monitor.libcamera.rules", Json.Array {})
 
 function createLibcamNode (parent, id, type, factory, properties)
-  local registered = mutils:register_cam_node (parent, id, factory, properties)
-  if not registered then
-    source = source or Plugin.find ("standard-event-source")
-    local e = source:call ("create-event", "create-libcamera-device-node",
-      parent, nil)
-    e:set_data ("factory", factory)
-    e:set_data ("node-properties", properties)
-    e:set_data ("node-sub-id", id)
-
-    EventDispatcher.push_event (e)
-  end
+  mutils:register_cam_node (parent, id, factory, properties)
 end
 
 SimpleEventHook {

src/scripts/monitors/v4l2/create-device.lua

@@ -14,17 +14,7 @@ config = {}
 config.rules = Conf.get_section_as_json ("monitor.v4l2.rules", Json.Array {})
 
 function createV4l2camNode (parent, id, type, factory, properties)
-  local registered = mutils:register_cam_node (parent, id, factory, properties)
-  if not registered then
-    source = source or Plugin.find ("standard-event-source")
-    local e = source:call ("create-event", "create-v4l2-device-node",
-      parent, nil)
-    e:set_data ("factory", factory)
-    e:set_data ("node-properties", properties)
-    e:set_data ("node-sub-id", id)
-
-    EventDispatcher.push_event (e)
-  end
+  mutils:register_cam_node (parent, id, factory, properties)
 end
 
 SimpleEventHook {