[Xen-changelog] [qemu-xen master] block: Open backing image in force share mode for size probe

[patchbot@xxxxxxx]

commit 7f53a8107386d2943ff83c3224775a3eea82b767
Author:     Fam Zheng <famz@xxxxxxxxxx>
AuthorDate: Fri Dec 15 16:04:45 2017 +0800
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue Jan 9 10:49:44 2018 -0600

    block: Open backing image in force share mode for size probe
    
    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@xxxxxxxxxx
    Signed-off-by: Fam Zheng <famz@xxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx>
    (cherry picked from commit cc954f01e3c004aad081aa36736a17e842b80211)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 9a1a0d1..f236431 100644
--- a/block.c
+++ b/block.c
@@ -4593,10 +4593,11 @@ 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);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#master

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