[libvirt] [Xen-devel] libvirt, libxl and QDISKs

[Jim Fehlig]

David Scott wrote:
>> Something like the attached, which seems to work well for me when
>> specifying driverName = qemu, e.g.
>>
>>      <disk type='file' device='disk'>
>>        <driver name='qemu'/>
>>        <source file='/var/lib/xen/images/sles11sp2-pv/disk0.raw'/>
>>        <target dev='xvda' bus='xen'/>
>>      </disk>
>
> This also works for me!

Good to hear.  I'll send the patch to the libvirt list.

>
> On a related note, what do you think about the attached patch? It
> allows the user to select a non-default qemu via the <emulator>
> element. My domain XML looked like this:
>
>   <devices>
>     <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator>

IMO, the possible emulators should be exposed in the capabilities.  E.g.
on a machine with both kvm and qemu, both emulators are shown as
possibilities for an hvm, x86_64 guest

# virsh capabilities
...
<guest>
  <os_type>hvm</os_type>
  <arch name='x86_64'>
  <wordsize>64</wordsize>
  <domain type='qemu'>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <machine>pc-1.1</machine>
    <machine canonical='pc-1.1'>pc</machine>
    <machine>pc-1.0</machine>
    <machine>pc-0.15</machine>
    <machine>pc-0.14</machine>
    <machine>pc-0.13</machine>
    <machine>pc-0.12</machine>
    <machine>pc-0.11</machine>
    <machine>pc-0.10</machine>
    <machine>isapc</machine>
  </domain>
  <domain type='kvm'>
    <emulator>/usr/bin/qemu-kvm</emulator>
    <machine>pc-1.1</machine>
    <machine canonical='pc-1.1'>pc</machine>
    <machine>pc-1.0</machine>
    <machine>pc-0.15</machine>
    <machine>pc-0.14</machine>
    <machine>pc-0.13</machine>
    <machine>pc-0.12</machine>
    <machine>pc-0.11</machine>
    <machine>pc-0.10</machine>
    <machine>isapc</machine>
  </domain>
   ....
</guest>
...

>     <disk device="disk" type="network">
>       <driver name='qemu'/>
>       <source protocol="rbd" name="rbd:rbd/ubuntu1204.img"/>
>       <target dev="hda"/>
>     </disk>
>     <graphics type="vnc" port="-1" autoport="yes" listen="0.0.0.0"/>
>   </devices>
>
> Now that upstream qemu is the default in xen-4.3, it seems useful to
> be able to select the traditional qemu for older VMs.

Agreed.  And reporting that both emulators exist via the capabilities
would be helpful for users.

>
> Also I backported this to my xen-4.2 system and used this patch + your
> patch + the previous 'stat()' fix to successfully start a VM on ceph
> storage via libvirt + libxl (my quest is almost complete!)

Nice!

> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
> index f549a5d..abbd3c0 100644
> --- a/src/libxl/libxl_conf.c
> +++ b/src/libxl/libxl_conf.c
> @@ -811,6 +811,30 @@ 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 (strstr(def->emulator, "/qemu-system-")) {
> +        d_config->b_info.device_model_version =
> +            LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
> +        return 0;
> +    }
>   

Here we could check the requested emulator against the capabilities, and
then do the proper mapping for device_model_version.

Do you have time for an upstream libvirt patch to expose the possible
emulators in the capabilities, along with this patch allowing the user
to specify one?

Regards,
Jim

> +    if (strstr(def->emulator, "/qemu-dm")) {
> +        d_config->b_info.device_model_version =
> +            LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL;
> +        return 0;
> +    }
> +    virReportError(VIR_ERR_INTERNAL_ERROR,
> +                   _("libxenlight doesn't support emulator '%s'"),
> +                   def->emulator);
> +    return -1;
> +}
> +
> +
> +int
>  libxlBuildDomainConfig(libxlDriverPrivatePtr driver,
>                         virDomainDefPtr def, libxl_domain_config *d_config)
>  {
> @@ -834,6 +858,10 @@ 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;
>   
> ------------------------------------------------------------------------