feat(xo-server/backup-ng): emit warning task when zstd is chosen but not supported (#4375)

See #3892

CHANGELOG.unreleased.md

@@ -12,6 +12,7 @@
 > Users must be able to say: “I had this issue, happy to know it's fixed”
 
 - [VM/Advanced] Fix `"vm.set_domain_type" is not a function` error on switching virtualization mode (PV/HVM) [#4348](https://github.com/vatesfr/xen-orchestra/issues/4348) (PR [#4504](https://github.com/vatesfr/xen-orchestra/pull/4504))
+- [Backup NG/logs] Show warning when zstd compression is selected but not supported [#3892](https://github.com/vatesfr/xen-orchestra/issues/3892) (PR [#4375](https://github.com/vatesfr/xen-orchestra/pull/4375)
 
 ### Released packages
 

packages/xo-server/src/xo-mixins/backups-ng/index.js

@@ -1146,6 +1146,21 @@ export default class BackupNg {
         $defer.call(xapi, 'deleteVm', snapshot)
       }
 
+      let compress = getJobCompression(job)
+      const pool = snapshot.$pool
+      if (
+        compress === 'zstd' &&
+        pool.restrictions.restrict_zstd_export !== 'false'
+      ) {
+        compress = false
+        logger.warning(
+          `Zstd is not supported on the pool ${pool.name_label}, the VM will be exported without compression`,
+          {
+            event: 'task.warning',
+            taskId,
+          }
+        )
+      }
       let xva: any = await wrapTask(
         {
           logger,
@@ -1153,7 +1168,7 @@ export default class BackupNg {
           parentId: taskId,
         },
         xapi.exportVm($cancelToken, snapshot, {
-          compress: getJobCompression(job),
+          compress,
         })
       )
       const exportTask = xva.task