Re: [PATCH 09/10] libxl: Stubdom emulator type

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Marek Marczykowski-Górecki wrote:
> Xen have feature of having device model in separate domain (called stub
> domain). Add a 'type' attribute to 'emulator' element to allow selecting
> such a configuration.

Or maybe 'mode', describing the mode in which the emulator runs: as a
process or as a VM.

>  Emulator path is still used for qemu running in dom0 (if
> any). Libxl currently do not allow to select stubdomain path.
>   

That seems to overload a single <emulator>.  Would it be better to have
multiple <emulators>?  E.g.

  <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator>
  <emulator mode='stubdomain'>/usr/lib/xen/bin/stubdom-dm</emulator>

> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> ---
>
> I think it would be good idea to introduce the same change to capabilities XML.
> The problem is I can't include domain_conf.h from capabilities.h, so probably
> that enum declaration needs to be moved to capabilities.h. Is it the right way?
> Or it should be done somehow different?
>
>  docs/formatdomain.html.in     | 14 ++++++++++++++
>  docs/schemas/domaincommon.rng | 23 ++++++++++++++++++++++-
>  src/conf/domain_conf.c        | 36 ++++++++++++++++++++++++++++++++++--
>  src/conf/domain_conf.h        |  9 +++++++++
>  src/libxl/libxl_conf.c        | 17 +++++++++++++++++
>  5 files changed, 96 insertions(+), 3 deletions(-)
>
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 38c42d5..4f539e2 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -1652,6 +1652,20 @@
>          The <a href="formatcaps.html">capabilities XML</a> specifies
>          the recommended default emulator to use for each particular
>          domain type / architecture combination.
> +
> +        <span class="since">Since 1.2.13</span>, the <code>emulator</code>
> +        element may contain <code>type</code> attribute. Possible values are:
> +        <dl>
> +          <dt><code>type='default'</code></dt>
> +          <dd>Equivalent to not setting <code>type</code> attribute at all.
> +          </dd>
> +
> +          <dt><code>type='stubdom'</code></dt>
> +          <dd>Launch emulator in stub domain (Xen only). The emulator path
> +          still indicate which binary is used in dom0 - there is no control
> +          which binary is used as a stub domain.
> +          </dd>
> +        </dl>
>        </dd>
>      </dl>
>  
> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
> index a4321f1..2a12073 100644
> --- a/docs/schemas/domaincommon.rng
> +++ b/docs/schemas/domaincommon.rng
> @@ -2519,7 +2519,28 @@
>      -->
>    <define name="emulator">
>      <element name="emulator">
> -      <ref name="absFilePath"/>
> +      <choice>
> +        <group>
> +          <optional>
> +            <attribute name="type">
> +              <choice>
> +                <value>qemu</value>
> +                <value>stubdom</value>
> +              </choice>
> +            </attribute>
> +          </optional>
> +          <ref name="absFilePath"/>
> +        </group>
> +        <group>
> +          <attribute name="type">
> +            <choice>
> +              <value>qemu</value>
> +              <value>stubdom</value>
> +            </choice>
> +          </attribute>
> +          <empty/>
> +        </group>
> +      </choice>
>      </element>
>    </define>
>    <!--
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 17b699a..c268091 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -741,6 +741,10 @@ VIR_ENUM_IMPL(virDomainDiskTray, VIR_DOMAIN_DISK_TRAY_LAST,
>                "closed",
>                "open");
>  
> +VIR_ENUM_IMPL(virDomainEmulatorType, VIR_DOMAIN_EMULATOR_TYPE_LAST,
> +              "qemu",
> +              "stubdom");
> +
>  VIR_ENUM_IMPL(virDomainRNGModel,
>                VIR_DOMAIN_RNG_MODEL_LAST,
>                "virtio");
> @@ -13712,6 +13716,14 @@ virDomainDefParseXML(xmlDocPtr xml,
>      }
>  
>      def->emulator = virXPathString("string(./devices/emulator[1])", ctxt);
> +    if ((tmp = virXPathString("string(./devices/emulator/@type)", ctxt))) {
> +        def->emulator_type = virDomainEmulatorTypeTypeFromString(tmp);
> +        VIR_FREE(tmp);
> +        if (def->emulator_type < 0) {
> +            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                           _("Unknown emulator type '%s'"), tmp);
> +        }
> +    }
>  
>      /* analysis of the disk devices */
>      if ((n = virXPathNodeSet("./devices/disk", ctxt, &nodes)) < 0)
> @@ -15690,6 +15702,14 @@ virDomainDefCheckABIStability(virDomainDefPtr src,
>          goto error;
>      }
>  
> +    if (src->emulator_type != dst->emulator_type) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                _("Target domain emulator type %s does not match source %s"),
> +                virDomainEmulatorTypeTypeToString(dst->emulator_type),
> +                virDomainEmulatorTypeTypeToString(src->emulator_type));
> +        goto error;
> +    }
> +
>      if (!virDomainDefFeaturesCheckABIStability(src, dst))
>          goto error;
>  
> @@ -19893,8 +19913,20 @@ virDomainDefFormatInternal(virDomainDefPtr def,
>      virBufferAddLit(buf, "<devices>\n");
>      virBufferAdjustIndent(buf, 2);
>  
> -    virBufferEscapeString(buf, "<emulator>%s</emulator>\n",
> -                          def->emulator);
> +    if (def->emulator ||
> +            def->emulator_type != VIR_DOMAIN_EMULATOR_TYPE_DEFAULT) {
> +        virBufferAddLit(buf, "<emulator");
> +        if (def->emulator_type != VIR_DOMAIN_EMULATOR_TYPE_DEFAULT) {
> +            virBufferAsprintf(buf, " type='%s'",
> +                              virDomainEmulatorTypeTypeToString(def->emulator_type));
> +        }
> +        if (!def->emulator) {
> +            virBufferAddLit(buf, "/>\n");
> +        } else {
> +            virBufferEscapeString(buf, ">%s</emulator>\n",
> +                                  def->emulator);
> +        }
> +    }
>  
>      for (n = 0; n < def->ndisks; n++)
>          if (virDomainDiskDefFormat(buf, def->disks[n], flags) < 0)
> diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
> index 28c6920..38b9037 100644
> --- a/src/conf/domain_conf.h
> +++ b/src/conf/domain_conf.h
> @@ -1918,6 +1918,13 @@ struct _virBlkioDevice {
>  };
>  
>  typedef enum {
> +    VIR_DOMAIN_EMULATOR_TYPE_DEFAULT,
> +    VIR_DOMAIN_EMULATOR_TYPE_STUBDOM,
> +
> +    VIR_DOMAIN_EMULATOR_TYPE_LAST
> +} virDomainEmulatorType;
> +
> +typedef enum {
>      VIR_DOMAIN_RNG_MODEL_VIRTIO,
>  
>      VIR_DOMAIN_RNG_MODEL_LAST
> @@ -2083,6 +2090,7 @@ struct _virDomainDef {
>  
>      virDomainOSDef os;
>      char *emulator;
> +    virDomainEmulatorType emulator_type;
>      /* These three options are of type virTristateSwitch,
>       * except VIR_DOMAIN_FEATURE_CAPABILITIES that is of type
>       * virDomainCapabilitiesPolicy */
> @@ -2841,6 +2849,7 @@ VIR_ENUM_DECL(virDomainGraphicsSpiceMouseMode)
>  VIR_ENUM_DECL(virDomainGraphicsVNCSharePolicy)
>  VIR_ENUM_DECL(virDomainHyperv)
>  VIR_ENUM_DECL(virDomainKVM)
> +VIR_ENUM_DECL(virDomainEmulatorType)
>  VIR_ENUM_DECL(virDomainRNGModel)
>  VIR_ENUM_DECL(virDomainRNGBackend)
>  VIR_ENUM_DECL(virDomainTPMModel)
> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index b1131ea..a84ce09 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -768,6 +768,23 @@ libxlMakeDomBuildInfo(virDomainDefPtr def,
>              b_info->device_model_version = libxlDomainGetEmulatorType(def);
>          }
>  
> +        /* In case of stubdom there will be two qemu instances:
> +         *  - in stubdom (libxl uses hardcoded path for this one),
> +         *  - in dom0 as a backend for stubdom (if needed).
>   

Your comment here provoked my thinking above about supporting multiple
<emulator>s.  ISTM there should be an <emulator> device for each of
these qemu instances.

> +         * Emulator path control only the second one. It makes a perfect sense
> +         * to use <emulator type='stubdom'/> (yes, without emulator path).
>   

I'm not so sure.  Maybe we should first add support in libxl for
specifying a stubdomain emulator path.

Regards,
Jim

> +         */
> +        if (def->emulator_type == VIR_DOMAIN_EMULATOR_TYPE_STUBDOM)
> +            libxl_defbool_set(&b_info->device_model_stubdomain, 1);
> +
> +        if (def->os.cmdline && def->os.cmdline[0]) {
> +            b_info->extra_hvm = virStringSplit(def->os.cmdline, " ", 0);
> +            if (b_info->extra_hvm == NULL) {
> +                virReportOOMError();
> +                return -1;
> +            }
> +        }
> +
>          if (def->nserials) {
>              if (def->nserials > 1) {
>                  virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
>   

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