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 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.
> 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, 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.
This is the main problem, I think it should be ok to leave the default 
type as IOEMU in libxl__device_nic_setdefault and set the type manually 
to VIF for PV guests in 
libxl_create.c:libxl__domain_build_info_setdefault, does this sound ok?
> Where * == current lib(xl) default and&  == proposed default after this change.
> and:
>          type=ioemu =>       LIBXL_NIC_TYPE_IOEMU to be renamed 
> LIBXL_NIC_TYPE_VIF_IOEMU.
>          type=vif => LIBXL_NIV_TYPE_VIF, no renaming proposed.
>
> But if my table is correct then LIBXL_NIC_TYPE_VIF_IOEMU is the right
> default and shouldn't be changed. Roger can you either confirm or
> correct my table.
>
> Ian.

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