[libvirt] [PATCH] qemu-capabilities: Fix query-cpu-model-expansion on s390 with older kernel

[Jiri Denemark]

On Thu, Jan 12, 2017 at 11:18:11 -0500, Collin L. Walling wrote:
> When running on s390 with a kernel that does not support cpu model checking and
> with a Qemu new enough to support query-cpu-model-expansion, the gathering of qemu
> capabilities will fail. Qemu responds to the query-cpu-model-expansion qmp
> command with an error because the needed kernel ioct does not exist. When this
> happens a guest cannot even be defined due to missing qemu capabilities data.
> 
> This patch fixes the problem by silently ignoring generic errors stemming from
> calls to query-cpu-model-expansion.
> 
> Reported-by: Farhan Ali <alifm at linux.vnet.ibm.com>
> Signed-off-by: Collin L. Walling <walling at linux.vnet.ibm.com>
> Signed-off-by: Jason J. Herne <jjherne at linux.vnet.ibm.com>
> ---
>  src/qemu/qemu_monitor_json.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
> index e767437..1662749 100644
> --- a/src/qemu/qemu_monitor_json.c
> +++ b/src/qemu/qemu_monitor_json.c
> @@ -5041,6 +5041,15 @@ qemuMonitorJSONGetCPUModelExpansion(qemuMonitorPtr mon,
>      if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
>          goto cleanup;
>  
> +    /* Some QEMU architectures have the query-cpu-model-expansion
> +     * command, but return 'GenericError' instead of simply omitting
> +     * the command entirely.
> +     */

Hmm, this comment says something a bit different than the commit
message. I hope the issue described by this comment was fixed in QEMU
within the same release the query-cpu-model-expansion command was
introduced. But we need to fix this nevertheless to address what the
commit message describes.

> +    if (qemuMonitorJSONHasError(reply, "GenericError")) {
> +        ret = 0;
> +        goto cleanup;
> +    }
> +
>      if (qemuMonitorJSONCheckError(cmd, reply) < 0)
>          goto cleanup;

However, we need to do a little bit more than just ignoring this error.
I'll send a v2 soon.

Jirka