Re: [PATCH] libxl: only query VNC when enabled

[Wei Liu <wl@xxxxxxx>]

On Thu, Oct 01, 2020 at 07:53:37PM -0400, Jason Andryuk wrote:
> QEMU without VNC support (configure --disable-vnc) will return an error
> when VNC is queried over QMP since it does not recognize the QMP
> command.  This will cause libxl to fail starting the domain even if VNC
> is not enabled.  Therefore only query QEMU for VNC support when using
> VNC, so a VNC-less QEMU will function in this configuration.
> 
> 'goto out' jumps to the call to device_model_postconfig_done(), the
> final callback after the chain of vnc queries.  This bypasses all the
> QMP VNC queries.
> 
> Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---
>  tools/libs/light/libxl_dm.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
> index a944181781..d1ff35dda3 100644
> --- a/tools/libs/light/libxl_dm.c
> +++ b/tools/libs/light/libxl_dm.c
> @@ -3140,6 +3140,7 @@ static void device_model_postconfig_chardev(libxl__egc 
> *egc,
>  {
>      EGC_GC;
>      libxl__dm_spawn_state *dmss = CONTAINER_OF(qmp, *dmss, qmp);
> +    const libxl_vnc_info *vnc = libxl__dm_vnc(dmss->guest_config);
>      const libxl__json_object *item = NULL;
>      const libxl__json_object *o = NULL;
>      int i = 0;
> @@ -3197,6 +3198,9 @@ static void device_model_postconfig_chardev(libxl__egc 
> *egc,
>          if (rc) goto out;
>      }
>  
> +    if (!vnc)
> +        goto out;
> +

I would rather this check be done in device_model_postconfig_vnc.

Does the following work for you?

diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
index a944181781bb..c5db755a65d7 100644
--- a/tools/libs/light/libxl_dm.c
+++ b/tools/libs/light/libxl_dm.c
@@ -3222,6 +3222,8 @@ static void device_model_postconfig_vnc(libxl__egc *egc,

     if (rc) goto out;

+    if (!vnc) goto out;
+
     /*
      * query-vnc response:
      * { 'enabled': 'bool', '*host': 'str', '*service': 'str' }
@@ -3255,7 +3257,8 @@ static void device_model_postconfig_vnc(libxl__egc *egc,
         if (rc) goto out;
     }

-    if (vnc && vnc->passwd && vnc->passwd[0]) {
+    assert(vnc);
+    if (vnc->passwd && vnc->passwd[0]) {
         qmp->callback = device_model_postconfig_vnc_passwd;
         libxl__qmp_param_add_string(gc, &args, "password", vnc->passwd);
         rc = libxl__ev_qmp_send(egc, qmp, "change-vnc-password", args);