New subject: [libvirt] [Xen-devel] libvirt, libxl and QDISKs

Friday, 26 April 2013

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;

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