Use min parameter to restrict live-migration config options

UpgradeImpact: IntOpt type provides min parameter to restrict integer's
minimum value in oslo.config, and will generate description about this
in the format like '# Minimum value: XXX', then we don't need round up
the minimum value quietly in code.

Change-Id: I54592ba4f46c2d6260f1513e5e29dd466c89724d

nova/conf/libvirt.py

@@ -25,12 +25,6 @@ from oslo_config import cfg
 
 from nova.conf import paths
 
-# Downtime period in milliseconds
-LIVE_MIGRATION_DOWNTIME_MIN = 100
-# Step count
-LIVE_MIGRATION_DOWNTIME_STEPS_MIN = 3
-# Delay in seconds
-LIVE_MIGRATION_DOWNTIME_DELAY_MIN = 10
 
 libvirt_group = cfg.OptGroup("libvirt",
                              title="Libvirt Options",
@@ -332,15 +326,14 @@ If set to 0, the hypervisor will choose a suitable default. Some hypervisors
 do not support this feature and will return an error if bandwidth is not 0.
 Please refer to the libvirt documentation for further details.
 """),
-    # TODO(hieulq): Need to add min argument by moving from
-    # LIVE_MIGRATION_DOWNTIME_MIN constant.
     cfg.IntOpt('live_migration_downtime',
                default=500,
+               min=100,
                help="""
 Maximum permitted downtime, in milliseconds, for live migration
 switchover.
 
-Will be rounded up to a minimum of %dms. You can increase this value
+Will be rounded up to a minimum of 100ms. You can increase this value
 if you want to allow live-migrations to complete faster, or avoid
 live-migration timeout errors by allowing the guest to be paused for
 longer during the live-migration switch over.
@@ -348,27 +341,25 @@ longer during the live-migration switch over.
 Related options:
 
 * live_migration_completion_timeout
-""" % LIVE_MIGRATION_DOWNTIME_MIN),
-    # TODO(hieulq): Need to add min argument by moving from
-    # LIVE_MIGRATION_DOWNTIME_STEPS_MIN constant.
+"""),
     cfg.IntOpt('live_migration_downtime_steps',
                default=10,
+               min=3,
                help="""
 Number of incremental steps to reach max downtime value.
 
-Will be rounded up to a minimum of %d steps.
-""" % LIVE_MIGRATION_DOWNTIME_STEPS_MIN),
-    # TODO(hieulq): Need to add min argument by moving from
-    # LIVE_MIGRATION_DOWNTIME_DELAY_MIN constant.
+Will be rounded up to a minimum of 3 steps.
+"""),
     cfg.IntOpt('live_migration_downtime_delay',
                default=75,
+               min=3,
                help="""
 Time to wait, in seconds, between each step increase of the migration
 downtime.
 
-Minimum delay is %d seconds. Value is per GiB of guest RAM + disk to be
+Minimum delay is 3 seconds. Value is per GiB of guest RAM + disk to be
 transferred, with lower bound of a minimum of 2 GiB per device.
-""" % LIVE_MIGRATION_DOWNTIME_DELAY_MIN),
+"""),
     cfg.IntOpt('live_migration_completion_timeout',
                default=800,
                mutable=True,

nova/virt/libvirt/migration.py

@@ -526,32 +526,6 @@ def downtime_steps(data_gb):
     steps = CONF.libvirt.live_migration_downtime_steps
     delay = CONF.libvirt.live_migration_downtime_delay
 
-    downtime_min = nova.conf.libvirt.LIVE_MIGRATION_DOWNTIME_MIN
-    steps_min = nova.conf.libvirt.LIVE_MIGRATION_DOWNTIME_STEPS_MIN
-    delay_min = nova.conf.libvirt.LIVE_MIGRATION_DOWNTIME_DELAY_MIN
-
-    # TODO(hieulq): Need to move min/max value into the config option,
-    # currently oslo_config will raise ValueError instead of setting
-    # option value to its min/max.
-    if downtime < downtime_min:
-        LOG.warning(_LW("Config option live_migration_downtime's value "
-                        "is less than minimum value %dms, rounded up to "
-                        "the minimum value and will raise ValueError in "
-                        "the future release."), downtime_min)
-        downtime = downtime_min
-
-    if steps < steps_min:
-        LOG.warning(_LW("Config option live_migration_downtime_steps's "
-                        "value is less than minimum value %dms, rounded "
-                        "up to the minimum value and will raise "
-                        "ValueError in the future release."), steps_min)
-        steps = steps_min
-    if delay < delay_min:
-        LOG.warning(_LW("Config option live_migration_downtime_delay's "
-                        "value is less than minimum value %dms, rounded "
-                        "up to the minimum value and will raise "
-                        "ValueError in the future release."), delay_min)
-        delay = delay_min
     delay = int(delay * data_gb)
 
     base = downtime / steps

releasenotes/notes/live-migrate-config-option-force-minimum-value-c62ad8481614b146.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    Three live-migration related configuration options were restricted
+    by minimum values since 16.0.0 and will now raise a ValueError if these
+    configuration options' values less than minimum values, instead of
+    logging warning before. These configuration options are:
+
+    - ``live_migration_downtime`` with minimum value 100
+    - ``live_migration_downtime_steps`` with minimum value 3
+    - ``live_migration_downtime_delay`` with minimum value 10