From: Peter Krempa <pkrempa@redhat.com>

While it may seem that zero detection is pointless for backing chain
layers other than the top one, which is usually the only one gettin
written to,  with block operations such as active-layer commit the
non-top layer may become active, in which case the VM wouldn't be
configured in accordance to the XML any more.

Similarly with snapshots a new image is introduced which would not get
zero detection enabled, but next start of the VM would enable it.

Fix this by propagating the zero detection setting for all layers.

This problem partially addresses one of the issues reported in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1120389

Fixes: 8a78f88a1a6 and a522c3044bd (effectively reverts them)
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
---
 src/qemu/qemu_domain.c                                      | 6 +-----
 .../xml2json/file-backing_basic-detect.json                 | 3 +++
 .../xml2json/file-backing_basic-unmap-detect.json           | 3 +++
 .../xml2json/file-backing_basic-unmap-ignore.json           | 3 +++
 tests/qemuxmlconfdata/disk-detect-zeroes.x86_64-latest.args | 6 +++---
 5 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index a42721efad..0ac9ae0658 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -9702,11 +9702,7 @@ qemuDomainPrepareDiskSourceData(virDomainDiskDef *disk,
     if (!disk)
         return;

-    /* transfer properties valid only for the top level image */
-    if (src == disk->src || src == disk->src->dataFileStore)
-        src->detect_zeroes = disk->detect_zeroes;
-
-    /* transfer properties valid for the full chain */
+    src->detect_zeroes = disk->detect_zeroes;
     src->iomode = disk->iomode;
     src->cachemode = disk->cachemode;
     src->discard = disk->discard;
diff --git a/tests/qemublocktestdata/xml2json/file-backing_basic-detect.json b/tests/qemublocktestdata/xml2json/file-backing_basic-detect.json
index c27233269b..773b7b3a02 100644
--- a/tests/qemublocktestdata/xml2json/file-backing_basic-detect.json
+++ b/tests/qemublocktestdata/xml2json/file-backing_basic-detect.json
@@ -16,6 +16,7 @@
 {
   "node-name": "node-b-f",
   "read-only": true,
+  "detect-zeroes": "on",
   "driver": "qed",
   "file": "node-b-s",
   "backing": "node-c-f"
@@ -30,6 +31,7 @@
 {
   "node-name": "node-c-f",
   "read-only": true,
+  "detect-zeroes": "on",
   "driver": "vmdk",
   "file": "node-c-s",
   "backing": "node-d-f"
@@ -49,6 +51,7 @@
 {
   "node-name": "node-d-f",
   "read-only": true,
+  "detect-zeroes": "on",
   "driver": "raw",
   "file": "node-d-s"
 }
diff --git a/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-detect.json b/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-detect.json
index 1ec0b8fffc..70faaa81de 100644
--- a/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-detect.json
+++ b/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-detect.json
@@ -18,6 +18,7 @@
   "node-name": "node-b-f",
   "read-only": true,
   "discard": "unmap",
+  "detect-zeroes": "unmap",
   "driver": "qed",
   "file": "node-b-s",
   "backing": "node-c-f"
@@ -33,6 +34,7 @@
   "node-name": "node-c-f",
   "read-only": true,
   "discard": "unmap",
+  "detect-zeroes": "unmap",
   "driver": "vmdk",
   "file": "node-c-s",
   "backing": "node-d-f"
@@ -53,6 +55,7 @@
   "node-name": "node-d-f",
   "read-only": true,
   "discard": "unmap",
+  "detect-zeroes": "unmap",
   "driver": "raw",
   "file": "node-d-s"
 }
diff --git a/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-ignore.json b/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-ignore.json
index 315a17323a..4bb964aaa4 100644
--- a/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-ignore.json
+++ b/tests/qemublocktestdata/xml2json/file-backing_basic-unmap-ignore.json
@@ -18,6 +18,7 @@
   "node-name": "node-b-f",
   "read-only": true,
   "discard": "ignore",
+  "detect-zeroes": "on",
   "driver": "qed",
   "file": "node-b-s",
   "backing": "node-c-f"
@@ -33,6 +34,7 @@
   "node-name": "node-c-f",
   "read-only": true,
   "discard": "ignore",
+  "detect-zeroes": "on",
   "driver": "vmdk",
   "file": "node-c-s",
   "backing": "node-d-f"
@@ -53,6 +55,7 @@
   "node-name": "node-d-f",
   "read-only": true,
   "discard": "ignore",
+  "detect-zeroes": "on",
   "driver": "raw",
   "file": "node-d-s"
 }
diff --git a/tests/qemuxmlconfdata/disk-detect-zeroes.x86_64-latest.args b/tests/qemuxmlconfdata/disk-detect-zeroes.x86_64-latest.args
index d959d4a717..6284c082b1 100644
--- a/tests/qemuxmlconfdata/disk-detect-zeroes.x86_64-latest.args
+++ b/tests/qemuxmlconfdata/disk-detect-zeroes.x86_64-latest.args
@@ -28,17 +28,17 @@ XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain--1-test/.config \
 -boot menu=on,strict=on \
 -device '{"driver":"piix3-usb-uhci","id":"usb","bus":"pci.0","addr":"0x1.0x2"}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-unmap-back.img","node-name":"libvirt-7-storage","auto-read-only":true,"discard":"unmap"}' \
--blockdev '{"node-name":"libvirt-7-format","read-only":true,"discard":"unmap","driver":"qcow2","file":"libvirt-7-storage","backing":null}' \
+-blockdev '{"node-name":"libvirt-7-format","read-only":true,"discard":"unmap","detect-zeroes":"unmap","driver":"qcow2","file":"libvirt-7-storage","backing":null}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-unmap.img","node-name":"libvirt-6-storage","auto-read-only":true,"discard":"unmap"}' \
 -blockdev '{"node-name":"libvirt-6-format","read-only":false,"discard":"unmap","detect-zeroes":"unmap","driver":"qcow2","file":"libvirt-6-storage","backing":"libvirt-7-format"}' \
 -device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x4","drive":"libvirt-6-format","id":"virtio-disk0","bootindex":2}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-on-back.img","node-name":"libvirt-5-storage","auto-read-only":true,"discard":"unmap"}' \
--blockdev '{"node-name":"libvirt-5-format","read-only":true,"discard":"unmap","driver":"qcow2","file":"libvirt-5-storage","backing":null}' \
+-blockdev '{"node-name":"libvirt-5-format","read-only":true,"discard":"unmap","detect-zeroes":"on","driver":"qcow2","file":"libvirt-5-storage","backing":null}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-on.img","node-name":"libvirt-4-storage","auto-read-only":true,"discard":"unmap"}' \
 -blockdev '{"node-name":"libvirt-4-format","read-only":false,"discard":"unmap","detect-zeroes":"on","driver":"qcow2","file":"libvirt-4-storage","backing":"libvirt-5-format"}' \
 -device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x5","drive":"libvirt-4-format","id":"virtio-disk1"}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-off-back.img","node-name":"libvirt-3-storage","auto-read-only":true,"discard":"unmap"}' \
--blockdev '{"node-name":"libvirt-3-format","read-only":true,"discard":"unmap","driver":"qcow2","file":"libvirt-3-storage","backing":null}' \
+-blockdev '{"node-name":"libvirt-3-format","read-only":true,"discard":"unmap","detect-zeroes":"off","driver":"qcow2","file":"libvirt-3-storage","backing":null}' \
 -blockdev '{"driver":"file","filename":"/var/lib/libvirt/images/detect-zeroes-off.img","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}' \
 -blockdev '{"node-name":"libvirt-2-format","read-only":false,"discard":"unmap","detect-zeroes":"off","driver":"qcow2","file":"libvirt-2-storage","backing":"libvirt-3-format"}' \
 -device '{"driver":"virtio-blk-pci","bus":"pci.0","addr":"0x6","drive":"libvirt-2-format","id":"virtio-disk2"}' \
-- 
2.51.1