feat(instances): the Migrate tab marks hosts it cannot use and files in the way

The Migrate tab offered every other host alike, and its plan showed
neither a file of the same name in a destination pool nor the disks of
the VM's next start, which the job then refused. Now:

- When the tab opens, the hosts are checked first: one that cannot be
  reached, or the VM's own host under another record (the same libvirt
  host UUID), is shown with why and cannot be chosen, and the disks of
  the first one left are checked. The job refuses the VM's own host
  under another name too.
- A pool of the destination that has a file of a disk's name is shown
  but cannot be chosen for it; a disk no pool can take refuses the form.
- The next start's file disks the migration does not carry are listed;
  one not on storage both hosts share refuses the form, as the job does.

instances/views.py

@@ -41,6 +41,7 @@ from libvirt import (VIR_DOMAIN_PAUSED,
                      VIR_DOMAIN_UNDEFINE_MANAGED_SAVE,
                      VIR_DOMAIN_UNDEFINE_SNAPSHOTS_METADATA,
                      VIR_DOMAIN_UNDEFINE_NVRAM,
+                     VIR_DOMAIN_XML_INACTIVE,
                      VIR_ERR_NO_SUPPORT,
                      libvirtError)
 from logs.audit import audit, audit_vm, changed_fields, failed_vm
@@ -910,6 +911,23 @@ def move_disk(request, pk):
     return _back(request, pk, "disks")
 
 
+@superuser_only
+def migrate_targets(request, pk):
+    """The Migrate tab's destinations that cannot be chosen, {id: why}: one
+    that cannot be reached, or the VM's own host under another record.
+    Loaded when the tab opens, so the page does not wait for the hosts."""
+    from instances.jobs import migration_target
+
+    instance = get_instance(request.user, pk)
+    refused = {}
+    for target in Compute.objects.exclude(pk=instance.compute_id):
+        try:
+            migration_target(instance, target.pk)
+        except libvirtError as err:
+            refused[target.pk] = error_text(request, err)
+    return JsonResponse(refused)
+
+
 @superuser_only
 def migrate_plan(request, pk):
     """The disks of the Migrate tab for the chosen destination, loaded when
@@ -923,15 +941,10 @@ def migrate_plan(request, pk):
     dest = None
     try:
         dest = wvmInstances(target.hostname, target.login, target.password, target.type)
-        pools = [{"name": name, "directory": directory, "free": pool.info()[3]}
-                 for name, (pool, directory) in sorted(dest.file_pools().items())]
-        disks = dest.disk_plan(instance.proxy, instance.proxy.instance.XMLDesc(0))
-        for disk in disks:
-            # a copy goes by default to the pool on the same directory, else the first
-            names = [pool["name"] for pool in pools if pool["directory"] == os.path.dirname(disk["path"])]
-            names = names or [pool["name"] for pool in pools]
-            disk["default"] = names[0] if names else None
-        context = {"disks": disks, "pools": pools, "shut_off": instance.proxy.get_status() == 5}
+        pools = [{"name": name, "free": pool.info()[3]} for name, (pool, directory) in sorted(dest.file_pools().items())]
+        domain = instance.proxy.instance
+        disks, pending = dest.migration_plan(instance.proxy, domain.XMLDesc(0), domain.XMLDesc(VIR_DOMAIN_XML_INACTIVE))
+        context = {"disks": disks, "pending": pending, "pools": pools, "shut_off": instance.proxy.get_status() == 5}
     except libvirtError as err:
         context = {"error": error_text(request, err)}
     finally: