Tolerance of pre-existing software-RAID

constants.py

@@ -181,3 +181,7 @@ def error_string(error, logname, with_hd):
     'var/lib/misc/ran-network-init',
     'var/lib/misc/ran-storage-init',
 ]
+
+# optional features
+FEATURES_DIR = "/etc/xensource/features"
+HAS_RAID_ASSEMBLE = os.path.exists(os.path.join(FEATURES_DIR, "raid-assemble"))

doc/features.txt

@@ -0,0 +1,18 @@
+Features flags
+==============
+
+Some host-installer features are not enabled by default, and
+downstream installers can activate them by creating a file in
+/etc/xensource/features/ in their installer filesystem.
+
+Currently available feature flags are:
+
+  raid-assemble
+
+    Detect Linux software-RAID (a.k.a "md") superblocks in disks, adds
+    a choice for the user to activate software RAID volumes, and do
+    not offer the user the ability to upgrade or restore a system on a
+    software-RAID device.
+
+    This only impacts the UI, the <assemble-raid/> answerfile
+    construct does not need this feature flag.

tui/installer/screens.py

@@ -229,7 +229,7 @@ def get_installation_type(answers):
     # RAID members, for filtering out from upgradable-products and
     # backups, and to decide whether to propose to activate existing RAID.
     raid_members = []
-    if "assemble-raid" not in answers:
+    if constants.HAS_RAID_ASSEMBLE and "assemble-raid" not in answers:
         for disk in diskutil.getQualifiedDiskList():
             rv, out = util.runCmd2([ 'mdadm', '--examine', disk ], with_stdout=True)
             if rv == 0 and re.search("Array UUID :", out):