exporter: Add USB hub abstraction for simpler device matching

The exporter config requires full @ID_PATH strings for every USB
resource, which are long and hard to maintain. Add a 'hubs' section
to the exporter config that defines USB hubs by name, base path,
and a mapping of logical port numbers to USB path suffixes.
Resources can then use 'hub' and 'port' in their match dict instead
of a raw @ID_PATH string.

For example, instead of:

  board1:
    USBSerialPort:
      match:
        '@ID_PATH': 'pci-0000:04:00.0-usb-0:2.2.3'

the config can be written as:

  hubs:
    a:
      base: 'pci-0000:04:00.0-usb-0:2'
      ports:
        7: '2.3'

  board1:
    USBSerialPort:
      match:
        hub: a
        port: 7

The expansion happens at config load time before any resource
matching, so it works with any USB resource type.

Signed-off-by: Simon Glass <sjg@chromium.org>

Author: sjg20

doc/configuration.rst

@@ -4402,6 +4402,77 @@ to achieve the same effect:
        match:
          '@ID_PATH': 'pci-0000:05:00.0-usb-3-1.4'
 
+.. _exporter-hub-abstraction:
+
+USB Hub Abstraction
+~~~~~~~~~~~~~~~~~~~
+When a lab uses USB hubs with many ports, the raw ``ID_PATH`` strings in
+match entries become long and hard to maintain.  The exporter supports a
+``hubs`` section that defines USB hubs by name, with a base path and a
+mapping from logical port numbers to USB path suffixes.  Resources can
+then use ``hub`` and ``port`` in their match dict instead of a raw
+``ID_PATH``.
+
+Define hubs at the top level of the exporter configuration:
+
+.. code-block:: yaml
+
+   hubs:
+     a:
+       base: 'pci-0000:00:14.0-usb-0:10'
+       ports:
+         1: '2.1'
+         2: '2.2'
+         3: '2.3'
+         # ...
+     b:
+       base: 'pci-0000:04:00.0-usb-0:2'
+       ports:
+         1: '1.1'
+         2: '1.2'
+         # ...
+
+Each hub has a ``base`` path (the PCI path up to the hub's root port) and
+a ``ports`` mapping from logical port number to the USB path suffix for
+that port.  The port suffixes depend on the hub's internal topology and
+must be determined for each hub model (for example by plugging a device
+into each port and checking ``udevadm info``).
+
+Resources reference a hub port using ``hub`` and ``port`` in their match
+dict.  For resources that need an ancestor match (like serial ports),
+add ``iface`` to specify the USB interface number:
+
+.. code-block:: yaml
+
+   board1:
+     USBSerialPort:
+       match:
+         hub: a
+         port: 3
+         iface: '1.0'
+
+     HIDRelay:
+       index: 4
+       match:
+         hub: a
+         port: 14
+
+When ``iface`` is present, the expansion produces an ``@ID_PATH`` (ancestor
+match) with the interface appended after a colon:
+``@ID_PATH: pci-0000:00:14.0-usb-0:10.2.3:1.0``.
+
+When ``iface`` is absent, the expansion produces a plain ``ID_PATH`` (direct
+match) with no interface suffix:
+``ID_PATH: pci-0000:00:14.0-usb-0:10.1.2``.
+
+Other match keys (such as ``ID_SERIAL_SHORT``) can be used alongside
+``hub``/``port`` and are preserved in the expanded match.  Resources that
+do not use hub/port matching (e.g. those matched by serial number) are
+unaffected.
+
+The ``hubs`` section is removed from the configuration data after
+expansion and does not appear as a resource group.
+
 Templating the Exporter Configuration
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 To reduce the amount of repeated declarations when many similar resources

doc/usage.rst

@@ -839,3 +839,49 @@ like this:
   $ labgrid-client -p example allow sirius/john
 
 To remove the allow it is currently necessary to unlock and lock the place.
+
+Simplifying USB device matching with hubs
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Labs with many USB devices often use multi-port USB hubs, and the raw
+``ID_PATH`` strings needed to match each device can be long and error-prone.
+The exporter supports a ``hubs`` section in the configuration file that maps
+logical hub names and port numbers to USB paths, so that resources can be
+described more concisely.
+
+For example, instead of writing::
+
+   board1:
+     USBSerialPort:
+       match:
+         '@ID_PATH': 'pci-0000:00:14.0-usb-0:10.2.3:1.0'
+
+you can define the hub once and reference it by name::
+
+   hubs:
+     a:
+       base: 'pci-0000:00:14.0-usb-0:10'
+       ports:
+         1: '2.1'
+         2: '2.2'
+         3: '2.3'
+
+   board1:
+     USBSerialPort:
+       match:
+         hub: a
+         port: 3
+         iface: '1.0'
+
+The ``iface`` field controls both the USB interface suffix and the match
+type: when present, the result is an ``@ID_PATH`` ancestor match with the
+interface appended (for serial ports and similar multi-interface devices);
+when absent, the result is a plain ``ID_PATH`` direct match (for relays,
+USB loaders, etc.).
+
+To determine the port mapping for a hub, plug a device into each port and
+check its path with ``udevadm info``.  The ``base`` is the common prefix
+and each port's suffix is the remainder.
+
+See :ref:`USB Hub Abstraction <exporter-hub-abstraction>` in the
+configuration reference for full details.

labgrid/remote/exporter.py

@@ -29,6 +29,82 @@
 reexec = False
 
 
+def _expand_hubs(data):
+    """Expand hub/port references in match dicts to ID_PATH values.
+
+    If the config data contains a top-level 'hubs' key, it is popped and
+    used to resolve any match dicts that contain 'hub' and 'port' keys
+    into a full ID_PATH string.
+
+    When 'iface' is also present, the result uses '@ID_PATH' (ancestor
+    match) with the interface appended after a colon.  Without 'iface',
+    the result uses 'ID_PATH' (direct match) with no interface suffix.
+
+    For example, given::
+
+        hubs:
+          a:
+            base: 'pci-0000:04:00.0-usb-0:2'
+            ports:
+              7: '2.3'
+
+    a match dict ``{'hub': 'a', 'port': 7, 'iface': '1.0'}`` becomes
+    ``{'@ID_PATH': 'pci-0000:04:00.0-usb-0:2.2.3:1.0'}``.
+
+    Without iface, ``{'hub': 'a', 'port': 7}`` becomes
+    ``{'ID_PATH': 'pci-0000:04:00.0-usb-0:2.2.3'}``.
+    """
+    hubs = data.pop("hubs", None)
+    if not hubs:
+        return
+
+    for group_name, group in data.items():
+        if not isinstance(group, dict):
+            continue
+        for resource_name, params in group.items():
+            if not isinstance(params, dict):
+                continue
+            match = params.get("match")
+            if not isinstance(match, dict):
+                continue
+
+            hub_name = match.get("hub")
+            port_num = match.get("port")
+            if hub_name is None and port_num is None:
+                continue
+            if hub_name is None or port_num is None:
+                raise ExporterError(
+                    f"{group_name}/{resource_name}: 'hub' and 'port' must both be specified in a match"
+                )
+
+            hub = hubs.get(hub_name)
+            if hub is None:
+                raise ExporterError(
+                    f"{group_name}/{resource_name}: hub '{hub_name}' is not defined in the hubs section"
+                )
+
+            ports = hub.get("ports", {})
+            # YAML may parse port keys as integers or strings
+            suffix = ports.get(port_num)
+            if suffix is None:
+                suffix = ports.get(str(port_num))
+            if suffix is None:
+                suffix = ports.get(int(port_num))
+            if suffix is None:
+                raise ExporterError(
+                    f"{group_name}/{resource_name}: port {port_num} is not defined in hub '{hub_name}'"
+                )
+
+            iface = match.get("iface")
+            del match["hub"]
+            del match["port"]
+            if iface is not None:
+                del match["iface"]
+                match["@ID_PATH"] = f"{hub['base']}.{suffix}:{iface}"
+            else:
+                match["ID_PATH"] = f"{hub['base']}.{suffix}"
+
+
 class ExporterError(Exception):
     pass
 
@@ -852,6 +928,7 @@ async def run(self) -> None:
             "name": self.name,
         }
         resource_config = ResourceConfig(self.config["resources"], config_template_env)
+        _expand_hubs(resource_config.data)
         for group_name, group in resource_config.data.items():
             group_name = str(group_name)
             for resource_name, params in group.items():