[libvirt] [PATCH v2] qemu: disable external snapshot of readonly disk

[John Ferlan]

On 11/9/18 3:00 AM, Nikolay Shirokovskiy wrote:
> Disable external snapshot of readonly disk for inactive domains
> as this operation is not very useful. As to active domains
> such snapshot was not possible before already but error message was
> not helpful so now it will be better.
> 
> Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy at virtuozzo.com>
> ---
> 
> Diff from v1 [1]
> ================
> 
> - move check to qemuDomainSnapshotPrepareDiskExternal
> - disable such snapshot for inactive domain as well
> 
> 
> [1]  [PATCH] qemu: snapshot: better error for active external readonly disk
> https://www.redhat.com/archives/libvir-list/2018-October/msg01322.html
>   continues in
> https://www.redhat.com/archives/libvir-list/2018-November/msg00265.html
> 
> 
>  src/qemu/qemu_driver.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 

Do you mind if I "merge" some details from the first patch on this to
generate the following commit message?:

    Disable external snapshot of a readonly disk for domains as
    this operation is not very useful. Such a snapshot is not
    possible for active domains but the error message from QEMU
    is more cryptic:

       error: internal error: unable to execute QEMU command 'transaction':
                           Could not create file: Permission denied

    This error at least makes the error more understandable for
active domains and disallows for inactive domains as well.


Reviewed-by: John Ferlan <jferlan at redhat.com>

John