From de79fad40fb6a970fab9dd566ed83ecf56877ea2 Mon Sep 17 00:00:00 2001
From: Peter Krempa <pkrempa@redhat.com>
Date: Wed, 26 Aug 2020 16:45:51 +0200
Subject: [PATCH] qemuBlockStorageSourceCreateDetectSize: Propagate cluster
 size for 'qcow2'

Propagate the cluster size from the original image as the user might
have configured a custom cluster size for performance reasons. Propagate
the cluster size of a qcow2 image to the new overlay or copy.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 src/qemu/qemu_block.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/qemu/qemu_block.c b/src/qemu/qemu_block.c
index 0113c64f0f..9095986f73 100644
--- a/src/qemu/qemu_block.c
+++ b/src/qemu/qemu_block.c
@@ -2789,6 +2789,12 @@ qemuBlockStorageSourceCreateDetectSize(virHashTablePtr blockNamedNodeData,
         return -1;
     }
 
+    /* propagate cluster size if the images are compatible */
+    if (templ->format == VIR_STORAGE_FILE_QCOW2 &&
+        src->format == VIR_STORAGE_FILE_QCOW2 &&
+        src->clusterSize == 0)
+        src->clusterSize = entry->clusterSize;
+
     if (src->format == VIR_STORAGE_FILE_RAW) {
         src->physical = entry->capacity;
     } else {