Re: [RFC] libxl hotplug / unplug emulated devices

[Wei Liu <wei.liu2@citrix.com>]

On Fri, May 20, 2016 at 06:45:04PM +0100, Wei Liu wrote:
> On Fri, May 20, 2016 at 05:38:44PM +0100, Ian Jackson wrote:
> > Wei Liu writes ("[RFC] libxl hotplug / unplug emulated devices"):
> > > Recently I got a report on xen-users@ about xl network-attach not
> > > working for HVM guest.
> > >
> > > I try to use
> > >   xl network-attach jessie-hvm 'bridge=xenbr0'
> > > and vif-bridge script complains that it can't add vifXX-emu to bridge.
> > >
> > > The underlying issue is that the vif spec provided defaults to
> > > emulated nic, but libxl only populates a pv nic but doesn't call out
> > > via QMP to QEMU to populate one. Note that this issue not only affects
> > > nic device but essentially all device types.
> >
> > Is it really sensible to offer emulated nic hotplug ?  That'd be
> > presented to the guest as pci hotplug, I guess ?
> >
> > > I also experimented with block device:
> > >   xl block-attach jessie-hvm 'phy:/dev/DATA/disk,hdb,w'
> > > and it succeed, only pv disk is populated though.
> >
> > That's what I would have expected.
> >
> > Maybe the fix should be that xl network-attach should default hotplug
> > nics to pv only.
> >
>
> Here is a patch to do this. :-)
>
> ---8<---
> From 0a0a0ac76f825983bb13d70e46a59cabb05ed77b Mon Sep 17 00:00:00 2001
> From: Wei Liu <wei.liu2@citrix.com>
> Date: Fri, 20 May 2016 18:16:05 +0100
> Subject: [PATCH for-4.7] libxl: nic type defaults to vif in hotplug for hvm guest
>
> We don't support plugging in emulated nic to a HVM guest.
>
> The "update_json" flag is only set when doing hotplug, so use that as an
> indicator in libxl__device_nic_add. The new hotplug flag to _setdefault
> function should be false in all other locations.
>
> This then requires saving nic type in JSON file, because we don't want
> the receiving end to recalculate the nic type.
>
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> ---
>  tools/libxl/libxl.c          | 6 +++---
>  tools/libxl/libxl_create.c   | 3 ++-
>  tools/libxl/libxl_dm.c       | 3 ++-
>  tools/libxl/libxl_internal.h | 3 ++-
>  4 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index c39d745..62e9294 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -3319,7 +3319,7 @@ out:
>  /******************************************************************************/
>
>  int libxl__device_nic_setdefault(libxl__gc *gc, libxl_device_nic *nic,
> -                                 uint32_t domid)
> +                                 uint32_t domid, bool hotplug)
>  {
>      int rc;
>
> @@ -3358,7 +3358,7 @@ int libxl__device_nic_setdefault(libxl__gc *gc, libxl_device_nic *nic,
>      case LIBXL_DOMAIN_TYPE_HVM:
>          if (!nic->nictype) {
>              if (libxl__device_model_version_running(gc, domid) ==
> -                LIBXL_DEVICE_MODEL_VERSION_NONE)
> +                LIBXL_DEVICE_MODEL_VERSION_NONE || hotplug)
>                  nic->nictype = LIBXL_NIC_TYPE_VIF;


@@ -3357,8 +3357,9 @@ int libxl__device_nic_setdefault(libxl__gc *gc, libxl_device_nic *nic,
     switch (libxl__domain_type(gc, domid)) {
     case LIBXL_DOMAIN_TYPE_HVM:
         if (!nic->nictype) {
-            if (libxl__device_model_version_running(gc, domid) ==
-                LIBXL_DEVICE_MODEL_VERSION_NONE)
+            if (hotplug ||
+                (libxl__device_model_version_running(gc, domid) ==
+                 LIBXL_DEVICE_MODEL_VERSION_NONE))
                 nic->nictype = LIBXL_NIC_TYPE_VIF;

I changed the snippet to above and will push this patch soon.

Wei.

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