The code that validates whether an internal snapshot is possible would
reject an empty but not-readonly drive. Since floppies can have this
property, add a check for emptiness.
---
 src/qemu/qemu_driver.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 388af4f6f..e39de625d 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -13825,7 +13825,8 @@ qemuDomainSnapshotPrepare(virConnectPtr conn,

         case VIR_DOMAIN_SNAPSHOT_LOCATION_NONE:
             /* Remember seeing a disk that has snapshot disabled */
-            if (!dom_disk->src->readonly)
+            if (!virStorageSourceIsEmpty(dom_disk->src) &&
+                !dom_disk->src->readonly)
                 forbid_internal = true;
             break;

-- 
2.12.2

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On 04/07/2017 11:50 AM, Peter Krempa wrote:
> The code that validates whether an internal snapshot is possible would
> reject an empty but not-readonly drive. Since floppies can have this
> property, add a check for emptiness.
> ---
>  src/qemu/qemu_driver.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

Took a little while to think about this one - but essentially because
LOCATION_NONE is being set when src->readonly (during XML parse) or when
virStorageSourceIsEmpty during virDomainSnapshotAlignDisks, that means
essentially that using LOCATION_NONE is "proper" for those disks and
thus if we find LOCATION_NONE that means we didn't set it that way and
thus the forbid_internal needs to be set.

ACK -

John

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