[libvirt] [PATCH v6 02/13] qemu: Detect support for vxhs

[Peter Krempa]

On Wed, Aug 30, 2017 at 18:46:02 -0400, John Ferlan wrote:
> Using the query-qmp-schema introspection - look for the 'vxhs'
> blockdevOptions type
> 
> Signed-off-by: John Ferlan <jferlan at redhat.com>
> ---
> 
>  This is new from v5, this is the way I figured out in order to
>  use the query-qmp-schema in order to determine if 'vxhs' was
>  possible. It sets the libvirt capability.
> 
>  src/qemu/qemu_capabilities.c                      | 4 ++++
>  src/qemu/qemu_capabilities.h                      | 3 +++
>  tests/qemucapabilitiesdata/caps_2.10.0.x86_64.xml | 1 +
>  3 files changed, 8 insertions(+)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index e7ea6f4..173bcf3 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c

[...]

> @@ -1811,6 +1814,7 @@ static struct virQEMUCapsStringFlags virQEMUCapsObjectPropsIntelIOMMU[] = {
>  static struct virQEMUCapsStringFlags virQEMUCapsQMPSchemaQueries[] = {
>      { "blockdev-add/arg-type/options/+gluster/debug-level", QEMU_CAPS_GLUSTER_DEBUG_LEVEL},
>      { "blockdev-add/arg-type/+gluster/debug", QEMU_CAPS_GLUSTER_DEBUG_LEVEL},
> +    { "blockdev-add/arg-type/+vxhs", QEMU_CAPS_VXHS},

I've just noticed that this is reported by qemu even if it isn't built
with libvxhs, thus this is not a 100% proof that qemu in fact supports
such volumes.

So with this you still might get a failure from qemu even if libvirt
thinks that it's supported. For other storage protocols we don't really
have capabilities. I'm not sure whether it's worth adding it. It will
catch that your qemu is too old, but won't if it has the feature
disabled.
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