Feed scan_info with fill_meta_at_scan_start

bliss/scanning/scan.py

@@ -1416,16 +1416,16 @@ class Scan:
 
             Method name can be either 'fill_meta_as_scan_start' or 'fill_meta_at_scan_end'
             """
-        for dev in self.acq_chain.nodes_list:
-            node = self.nodes.get(dev)
-            if node is None:
-                # prepare has not finished ?
-                continue
+        for acq_obj in self.acq_chain.nodes_list:
             with KillMask(masked_kill_nb=1):
-                meth = getattr(dev, method_name)
-                tmp = meth(self.user_scan_meta)
-            if tmp:
-                update_node_info(node, tmp)
+                fill_meta = getattr(acq_obj, method_name)
+                metadata = fill_meta(self.user_scan_meta)
+            if metadata is not None:
+                node = self.nodes.get(acq_obj)
+                if node is not None:
+                    update_node_info(node, metadata)
+                if method_name == "fill_meta_at_scan_start":
+                    self._scan_info._set_device_meta(acq_obj, metadata)
 
     def run(self):
         """Run the scan

bliss/scanning/scan_info.py

@@ -263,6 +263,24 @@ class ScanInfo(dict):
         info = self._scan_info.setdefault("sequence-info", {})
         info["scan-count"] = int(scan_count)
 
+    def _get_key_from_acq_obj(self, acq_obj):
+        """Used device key from an acq_obj"""
+        return f"{str(id(acq_obj))}:{acq_obj.name}"
+
+    def _set_device_meta(self, acq_obj, metadata: typing.Dict):
+        """Protected function called by the scan to feed the device info after
+        the device preparation.
+
+        Argument:
+            acq_obj: A device though its acquisition object
+            metadata: A dictionary of basic python types.
+                      Few reserved keys could be ignored.
+        """
+        devices = self.setdefault("devices", {})
+        name = self._get_key_from_acq_obj(acq_obj)
+        device = devices.setdefault(name, {})
+        device.update(metadata)
+
     def _get_channels_dict(self, acq_object, channels_dict):
         scalars = channels_dict.setdefault("scalars", [])
         spectra = channels_dict.setdefault("spectra", [])

tests/scans/test_data_watch.py

@@ -17,6 +17,7 @@ from bliss.scanning.acquisition.counter import SamplingCounterAcquisitionSlave
 from bliss.scanning.acquisition.mca import McaAcquisitionSlave
 from bliss.scanning.acquisition.motor import LinearStepTriggerMaster
 from bliss.scanning.scan import Scan
+from bliss.scanning.scan_info import ScanInfo
 from bliss.data.scan import watch_session_scans, ScansObserver, ScansWatcher
 from bliss.scanning.chain import AcquisitionChain
 from bliss.common import scans
@@ -460,6 +461,10 @@ def test_scan_observer(session, diode_acq_device_factory, mocker):
     master = SoftwareTimerMaster(0.1, npoints=1)
     chain.add(master, acquisition_device_1)
     scan = Scan(chain, "test", save=False)
+
+    meta = {"kind": "foo"}
+    acquisition_device_1.fill_meta_at_scan_start = mocker.Mock(return_value=meta)
+
     try:
         scan.run()
     finally:
@@ -470,11 +475,20 @@ def test_scan_observer(session, diode_acq_device_factory, mocker):
     observer.on_scan_created.assert_called_once()
     observer.on_scan_started.assert_called_once()
     observer.on_scan_finished.assert_called_once()
+
+    # Check that the scan_info looks like what it is expected
+    sf = ScanInfo()
+    device_key = sf._get_key_from_acq_obj(acquisition_device_1)
+
     call = observer.on_scan_created.call_args_list[0]
     scan_info = call[0][1]
     assert "positioners_start" in scan_info["positioners"]
     assert "start_timestamp" in scan_info
 
+    call = observer.on_scan_started.call_args_list[0]
+    scan_info = call[0][1]
+    assert "kind" in scan_info["devices"][device_key]
+
     call = observer.on_scan_finished.call_args_list[0]
     scan_info = call[0][1]
     assert "end_timestamp" in scan_info