[libvirt] [PATCH] libxl: allow an <emulator> to be selected in the domain config XML

[Jim Fehlig]

David Scott wrote:
> The emulator path supplied can be any valid path on the system.
>
> Note that when setting a device_model, libxl needs us to set the
> device_model_version too. The device_model_version can be either
>
>   ...QEMU_XEN: meaning "upstream qemu", the default in xen-4.3 onwards
>   ...QEMU_XEN_TRADITIONAL: the old xen-specific fork
>
> We detect the device_model_version by examining the qemu filename:
> if it is "qemu-dm" then it's the old xen-specific fork. If anything
> else then we assume "upstream qemu" (whose filename may change
> in future). Note that if you are using a wrapper script to (eg)
> adjust the arguments of the old qemu during development, you will
> have to ensure the wrapper script also has the name "qemu-dm", by
> placing it in a separate directory.
>   

That is unfortunate.  Users could have existing config with
<emulator>/usr/bin/my-qemu-dm</emulator> which works with the legacy
stack but not with libxl right?  Is it possible to safely query the
binary to determine if it is qemu-dm?

Regards,
Jim

> Signed-off-by: David Scott <dave.scott at eu.citrix.com>
> ---
>  src/libxl/libxl_conf.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 44 insertions(+), 0 deletions(-)
>
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index 7e0753a..2aa5a62 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -788,6 +788,46 @@ libxlMakeCapabilities(libxl_ctx *ctx)
>  }
>  
>  int
> +libxlMakeEmulator(virDomainDefPtr def, libxl_domain_config *d_config)
> +{
> +    /* No explicit override means use the default */
> +    if (!def->emulator) {
> +        return 0;
> +    }
> +
> +    if (!virFileExists(def->emulator)) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR,
> +                       _("emulator '%s' not found"),
> +                       def->emulator);
> +        return -1;
> +    }
> +
> +    VIR_FREE(d_config->b_info.device_model);
> +    if ((d_config->b_info.device_model = strdup(def->emulator)) == NULL) {
> +        virReportOOMError();
> +        return -1;
> +    }
> +
> +    /* N.B. from xen/tools/libxl/libxl_types.idl:
> +     * "If setting device_model you must set device_model_version too."
> +     *
> +     * The xen-4.3 and later default is "upstream qemu" (QEMU_XEN)
> +     * so we make that the default and special-case the old-style
> +     * "traditional qemu" (QEMU_XEN_TRADITIONAL)
> +     */
> +
> +    d_config->b_info.device_model_version =
> +        LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
> +
> +    if (STREQ(basename(def->emulator), "qemu-dm"))
> +        d_config->b_info.device_model_version =
> +            LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL; 
> +
> +    return 0;
> +}
> +
> +
> +int
>  libxlBuildDomainConfig(libxlDriverPrivatePtr driver,
>                         virDomainDefPtr def, libxl_domain_config *d_config)
>  {
> @@ -811,6 +851,10 @@ libxlBuildDomainConfig(libxlDriverPrivatePtr driver,
>          goto error;
>      }
>  
> +    if (libxlMakeEmulator(def, d_config) < 0) {
> +        goto error;
> +    }
> +
>      d_config->on_reboot = def->onReboot;
>      d_config->on_poweroff = def->onPoweroff;
>      d_config->on_crash = def->onCrash;
>