From 20103e6ef28af483bb8aa54b1272fbd480b61aa4 Mon Sep 17 00:00:00 2001
From: Fam Zheng <famz@redhat.com>
Date: Mon, 15 Jan 2018 06:15:18 +0100
Subject: [PATCH 08/12] block: Open backing image in force share mode for size
 probe

RH-Author: Fam Zheng <famz@redhat.com>
Message-id: <20180115061518.16303-1-famz@redhat.com>
Patchwork-id: 78570
O-Subject: [RHV7.5 qemu-kvm-rhev PATCH] block: Open backing image in force share mode for size probe
Bugzilla: 1526212
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

Management tools create overlays of running guests with qemu-img:

  $ qemu-img create -b /image/in/use.qcow2 -f qcow2 /overlay/image.qcow2

but this doesn't work anymore due to image locking:

    qemu-img: /overlay/image.qcow2: Failed to get shared "write" lock
    Is another process using the image?
    Could not open backing image to determine size.
Use the force share option to allow this use case again.

Cc: qemu-stable@nongnu.org
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit cc954f01e3c004aad081aa36736a17e842b80211)
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index b5736dd..17629ab 100644
--- a/block.c
+++ b/block.c
@@ -4515,10 +4515,11 @@ void bdrv_img_create(const char *filename, const char *fmt,
         back_flags = flags;
         back_flags &= ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
 
+        backing_options = qdict_new();
         if (backing_fmt) {
-            backing_options = qdict_new();
             qdict_put_str(backing_options, "driver", backing_fmt);
         }
+        qdict_put_bool(backing_options, BDRV_OPT_FORCE_SHARE, true);
 
         bs = bdrv_open(full_backing, NULL, backing_options, back_flags,
                        &local_err);
-- 
1.8.3.1