'qemuDomainPrepareDiskSourceData' propagates 'detect_zeroes' only for the disk source image, but the mirror destination has the ambition to replace the disk source when the job is finished, so we need to propagate the 'detect_zeroes' setting also in that case. Unfortunately it would become very hairy to either set 'disk->mirror' sooner or propagate that we want this done into 'qemuDomainPrepareDiskSourceData', so the most straightforward solution is to do the propagation inside 'qemuDomainBlockCopyCommon'. Closes: https://gitlab.com/libvirt/libvirt/-/issues/277 Signed-off-by: Peter Krempa <pkrempa(a)redhat.com&gt; --- src/qemu/qemu_driver.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index e417d358cd..4fc998cde5 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -14977,6 +14977,14 @@ qemuDomainBlockCopyCommon(virDomainObj *vm, if (qemuDomainPrepareStorageSourceBlockdev(disk, n, priv, cfg) < 0) goto endjob; } + + /* 'qemuDomainPrepareStorageSourceBlockdev' calls + * 'qemuDomainPrepareDiskSourceData' which propagates 'detect_zeroes' + * into the topmost virStorage source of the disk chain. + * Since 'mirror' has the ambition to replace it we need to propagate + * it into the mirror too. We do it directly as otherwise we'd need + * to modify all callers of 'qemuDomainPrepareStorageSourceBlockdev' */ + mirror->detect_zeroes = disk->detect_zeroes; } /* If reusing an external image that includes a backing file but the user -- 2.35.1