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From bcc312ef8d0c8ff3c8743e01bd24fd26c4cc96f6 Mon Sep 17 00:00:00 2001
From: Max Reitz <>
Date: Sun, 19 Jan 2014 18:07:57 +0100
Subject: [PATCH 23/34] block/drive-mirror: Check for NULL backing_hd

RH-Author: Max Reitz <>
Message-id: <>
Patchwork-id: 56816
O-Subject: [RHEL-7.0 qemu-kvm PATCH v2 3/7] block/drive-mirror: Check for NULL backing_hd
Bugzilla: 921890
RH-Acked-by: Fam Zheng <>
RH-Acked-by: Kevin Wolf <>
RH-Acked-by: Jeffrey Cody <>

BZ: 921890

It should be possible to execute the QMP "drive-mirror" command in
"none" sync mode and "absolute-paths" mode even for block devices
lacking a backing file.

"absolute-paths" does in fact not require a backing file to be present,
as can be seen from the "top" sync mode code path. "top" basically
states that the device should indeed have a backing file - however, the
current code catches the case if it doesn't and then simply treats it as
"full" sync mode, creating a target image without a backing file (in
"absolute-paths" mode). Thus, "absolute-paths" does not imply the target
file must indeed have a backing file.

Therefore, the target file may be left unbacked in case of "none" sync
mode as well, if the specified device is not backed either. Currently,
qemu will crash trying to dereference the backing file pointer since it
assumes that it will always be non-NULL in that case ("none" with

Signed-off-by: Max Reitz <>
Reviewed-by: Wenchao Xia <>
Reviewed-by: Eric Blake <>
Signed-off-by: Kevin Wolf <>
(cherry picked from commit 1452686495922b81d6cf43edf025c1aef15965c0)

Signed-off-by: Max Reitz <>
 blockdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Signed-off-by: Miroslav Rezanina <>
 blockdev.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 0ba2504..06bbf30 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1611,7 +1611,9 @@ void qmp_drive_mirror(const char *device, const char *target,
-    if (sync == MIRROR_SYNC_MODE_FULL && mode != NEW_IMAGE_MODE_EXISTING) {
+    if ((sync == MIRROR_SYNC_MODE_FULL || !source)
+        && mode != NEW_IMAGE_MODE_EXISTING)
+    {
         /* create new image w/o backing file */
         assert(format && drv);
         bdrv_img_create(target, format,