Add config option for fallocate_reserve

In order to prevent disks from filling up, add the option to configure
fallocate_reserve parameter in account-server.conf,
container-server.conf, and object-server.conf, as described in
https://docs.openstack.org/swift/latest/admin_guide.html#preventing-disk-full-scenarios

This change adds the config option file-allocation-reserve with a
default of 0.

Change-Id: Ib396a151250bb8d1733f9b5b9cab7eb506c9f6c6
Closes-Bug: 1872069

config.yaml

@@ -126,6 +126,13 @@ options:
     type: int
     description: |
       Timeout value used when copying account/container/object data between nodes.
+  file-allocation-reserve:
+    default: 0
+    type: int
+    description: |
+      Set the reserve space for the swift filesystem mounts.
+      If a disk has less than this amount of space (in bytes) free, writes
+      will be handed off to another disk in the ring.
   nagios-check-params:
     default: "-m -r 60 180 10 20"
     type: string

lib/swift_storage_context.py

@@ -102,6 +102,7 @@ class SwiftStorageServerContext(OSContextGenerator):
                 'object-replicator-concurrency'),
             'object_rsync_timeout': config('object-rsync-timeout'),
             'object_handoffs_first': config('object-handoffs-first'),
+            'fallocate_reserve': config('file-allocation-reserve'),
             'statsd_host': config('statsd-host'),
             'statsd_port': config('statsd-port'),
             'statsd_sample_rate': config('statsd-sample-rate'),

templates/account-server.conf

@@ -5,6 +5,9 @@ workers = {{ workers }}
 {% if node_timeout -%}
 node_timeout = {{ node_timeout }}
 {%- endif %}
+{% if fallocate_reserve != 0 %}
+fallocate_reserve = {{ fallocate_reserve }}
+{% endif %}
 
 {% if statsd_host %}
 log_statsd_host = {{ statsd_host }}

templates/container-server.conf

@@ -5,6 +5,9 @@ workers = {{ workers }}
 {% if node_timeout -%}
 node_timeout = {{ node_timeout }}
 {%- endif %}
+{% if fallocate_reserve != 0 %}
+fallocate_reserve = {{ fallocate_reserve }}
+{% endif %}
 
 {% if statsd_host %}
 log_statsd_host = {{ statsd_host }}

templates/object-server.conf

@@ -5,6 +5,9 @@ workers = {{ workers }}
 {% if node_timeout -%}
 node_timeout = {{ node_timeout }}
 {%- endif %}
+{% if fallocate_reserve != 0 %}
+fallocate_reserve = {{ fallocate_reserve }}
+{% endif %}
 
 {% if statsd_host %}
 log_statsd_host = {{ statsd_host }}

unit_tests/test_swift_storage_context.py

@@ -96,6 +96,7 @@ class SwiftStorageContextTests(CharmTestCase):
         self.test_config.set('object-max-connections', '10')
         self.test_config.set('object-rsync-timeout', '950')
         self.test_config.set('object-handoffs-first', True)
+        self.test_config.set('file-allocation-reserve', '10737418240')
         ctxt = swift_context.SwiftStorageServerContext()
         result = ctxt()
         ex = {
@@ -112,6 +113,7 @@ class SwiftStorageContextTests(CharmTestCase):
             'container_max_connections': '10',
             'object_max_connections': '10',
             'object_rsync_timeout': '950',
+            'fallocate_reserve': '10737418240',
             'standalone_replicator': True,
             'object_handoffs_first': True,
             'statsd_host': '',