Added discard-no-unref support to CL 4.8

The discard-no-unref was introduced to qemu to counteract fragmentation. Without this, qcow2 images would grow over 100% of their size. See https://patchew.org/QEMU/20230602124747.1544077-1-jean-louis@dupond.be/

I have added the option to ovirt-engine so that this flag is enabled by default on hosts with cluster level compatibility level 4.8. The EnableQemuDiscardNoUnref option can be enabled/disabled in the config. The Virtual Disk option 'Enable Discard' also needs to be active before this flag is enabled.

Signed-off-by: Brooklyn Dewolf <contact@brooklyn.gent>

backend/manager/modules/common/src/main/java/org/ovirt/engine/core/common/config/ConfigValues.java

@@ -1631,6 +1631,9 @@ public enum ConfigValues {
     @TypeConverterAttribute(Boolean.class)
     IsDedicatedSupported,
 
+    @TypeConverterAttribute(Boolean.class)
+    EnableQemuDiscardNoUnref,
+
     Invalid;
 
     private ClientAccessLevel accessLevel;

backend/manager/modules/vdsbroker/src/main/java/org/ovirt/engine/core/vdsbroker/builder/vminfo/LibvirtVmXmlBuilder.java

@@ -2291,6 +2291,9 @@ private void writeDiskDriver(VmDevice device, Disk disk, DiskVmElement dve, int
         writer.writeAttributeString("name", "qemu");
         if (dve.isPassDiscard()) {
             writer.writeAttributeString("discard", "unmap");
+            if ((boolean) Config.getValue(ConfigValues.EnableQemuDiscardNoUnref, vm.getClusterCompatibilityVersion().toString())) {
+                writer.writeAttributeString("discard_no_unref", "on");
+            }
         }
         if (pinTo > 0) {
             writer.writeAttributeString("iothread", String.valueOf(pinTo));

packaging/dbscripts/upgrade/pre_upgrade/0000_config.sql

@@ -974,6 +974,8 @@ select fn_db_add_config_value_for_versions_up_to('ParallelMigrationsSupported',
 select fn_db_add_config_value_for_versions_up_to('ParallelMigrationsSupported', 'true', '4.8');
 select fn_db_add_config_value_for_versions_up_to('IsDedicatedSupported', 'false', '4.6');
 select fn_db_add_config_value_for_versions_up_to('IsDedicatedSupported', 'true', '4.8');
+select fn_db_add_config_value_for_versions_up_to('EnableQemuDiscardNoUnref', 'false', '4.7');
+select fn_db_add_config_value_for_versions_up_to('EnableQemuDiscardNoUnref', 'true', '4.8');
 
 -- Incremental backup
 select fn_db_add_config_value_for_versions_up_to('IsIncrementalBackupSupported', 'false', '4.4');

packaging/etc/engine-config/engine-config.properties

@@ -615,3 +615,6 @@ CertExpirationWarnPeriodInDays.description=Number of days to issue warnings befo
 CertExpirationWarnPeriodInDays.type=Integer
 VdsCertificateValidityInDays.description=Number of days which the hypervisor certificate is valid for.
 VdsCertificateValidityInDays.type=Integer
+# Discard no Unref
+EnableQemuDiscardNoUnref.description=Enable the QEMU discard-no-unref feature.
+EnableQemuDiscardNoUnref.type=Boolean