fix InvalidSharedStorage exception message

The exception message for InvalidSharedStorage is grammatically
complex and ignores the possibility of block migration, which
results in a misleading and confusing message for the user.

Change it to something simpler and more accurate.

Change-Id: Icfc8e151a4ea36ec303f0b8c2e1dc9e6f0bd5925
Closes-Bug: #1690890
(cherry picked from commit 902b7bf6f5425824a0661b8e4beac4a894749c03)

diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 0e8fe0702c149e7a11c4f9a37beea89407e483e3..068c51318e4d435cefb78676b9dc46b5b72b2fde 100644 (file)
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -5784,10 +5784,8 @@ class LibvirtDriver(driver.ComputeDriver):
                     raise exception.MigrationPreCheckError(reason=msg)
         elif not (dest_check_data.is_shared_block_storage or
                   dest_check_data.is_shared_instance_path):
-            reason = _("Live migration can not be used "
-                       "without shared storage except "
-                       "a booted from volume VM which "
-                       "does not have a local disk.")
+            reason = _("Shared storage live-migration requires either shared "
+                       "storage or boot-from-volume with no local disks.")
             raise exception.InvalidSharedStorage(reason=reason, path=source)
 
         # NOTE(mikal): include the instance directory name here because it