Re: [Xen-devel] [PATCH v6 10/13] libxl: set nic type to VIF by default

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Ian Campbell wrote:
> On Thu, 2012-06-28 at 10:22 +0100, Roger Pau Monne wrote:
> > Ian Campbell wrote:
> > > On Tue, 2012-06-26 at 17:58 +0100, Pasi KÃrkkÃinen wrote:
> > > > On Tue, Jun 26, 2012 at 05:20:35PM +0100, Roger Pau Monne wrote:
> > > > > Ian Jackson wrote:
> > > > > > Roger Pau Monne writes ("[PATCH v6 10/13] libxl: set nic type to VIF by 
> > > > > > default"):
> > > > > > > Set the default value for nic interfaces to VIF, since it used to be
> > > > > > > IOEMU, even for PV guests.
> > > > > > If your renaming of IOEMU to VIF_IOEMU is correct, does this not stop
> > > > > > HVM guests getting emulated network interfaces by default ?
> > > > > Yes, if you want emulated interfaces with HVM guests you should use
> > > > > 'type=ioemu', that's how it has always been right?
> > > > With Xen 4.1 you don't have to use "type=ioemu". Emulated interfaces seem to work OK 
> > > > without "type=ioemu".
> > > > (at least with xm/xend). And if you actually do add "type=ioemu" it will break 
> > > > PVHVM for Linux guests..
> > > >
> > > > Quote from: http://wiki.xen.org/wiki/XenLinuxPVonHVMdrivers
> > > >
> > > > "NOTE! If you have "type=ioemu" specified for the "vif"-line, PVHVM
> > > > drivers WILL NOT work! Don't specify "type" parameter for the vif.
> > > > (with type=ioemu the pvhvm nic in the VM will have mac address full of
> > > > zeroes - and thus won't work!). "
> > > mac=00:00:00:00:00 is certainly a bug, if (lib)xl behaves this way too
> > > then we should fix it.
> > >
> > > But surely type=ioemu is supposed to mean "only emulated"? In which case
> > > the actual xend bug is that it created a PV VIF at all.
> > Currently there's no network type that means "emulated only", we have
> > VIF and VIF_IOEMU.
> Ah, ok, yes I'm confused.
>
> > > What are the options here? I think they are, with their (lib)xl
> > > behaviour:
> > >
> > >                 PV                              HVM
> > > type=ioemu      meaningless / an error          emulated device + paravirt VIF*
> > > type=vif        paravirt VIF device*&               paravirt VIF device only&
> > You are missing a row, the default one when user doesn't specify
> > anything,
> That was supposed to be indicated by the * (now) and&  (after your
> patch) symbols above.
>
> >   this currently is:
> >
> >         PV                              HVM
> > default nic type is set to IEOMU        nic type is set to IOEMU
> >
> > In the past this was not a problem, since when the guest is PV, we
> > didn't launch Qemu, and thus the tap device was never created and the
> > hotplug scripts were not launched. Now that we launch hotplug scripts
> > from libxl this is a problem, because when we call libxl_device_nic_add,
> > libxl has no idea if the domain is a PV or HVM guest, and only sees the
> > network type, which is set to IOEMU by default.
> It has a domid so it can ask and/or propagate it down to setdefaults.
I think the most suitable place is 
libxl_create.c:initiate_domain_create, which also sets the defaults for 
disk devices, so I think it's adequate to place something like:
if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_PV) {
    for (i = 0; i < d_config->num_vifs; i++) {
        d_config->vifs[i].nictype = LIBXL_NIC_TYPE_VIF;
    }
}


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