Re: Number of NICs per VM with qemu-upstream (Was: Re: Re: [Xen-users] libvirt <emulator> /usr/local/lib/xen/bin/qemu-dm <emulator> did not work on xen-4.4)

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2014-11-17 at 13:00 +0000, Stefano Stabellini wrote:
> On Mon, 17 Nov 2014, Ian Campbell wrote:
> > On Sat, 2014-11-15 at 10:16 +0800, hanyandong wrote:
> > > By the way, how many NICs can I apply to a VM?
> > > 
> > > On xen-4.4.0, Using qemu-dm, I can apply 8 NIC to a VM, but using
> > > qemu-system-i386, I can only apply 4 NICs to an VM?
> > > is it normal?
> > 
> > I've no idea, CCing the qemu maintainers.
> > 
> > I'd have expected the number of PV nics to be completely independent of
> > the device mode, so I suppose you mean emulated NICs?
> 
> I can pass 4 emulated NICs maximum, but you can easily reach 8 if you
> use PV NICs instead. Just pass 'type=pv' like this:
> 
> vif=['', '', '', '', 'type=pv', 'type=pv', 'type=pv', 'type=pv']
> 
> it is going to create 4 emulated nics and 4 pv nics. The 4 emulated nics
> also have 4 corresponding pv nics. The emulated nics get disconnected
> soon after boot by the guest operating system (if it has pv drivers
> installed, such as Linux). So overall once the boot sequence is fully
> completed you'll end up with the 8 pv nics that you want.

I wonder if we should do something in (lib)xl such that by default the
first 4 NICs have type LIBXL_NIC_TYPE_VIF_IOEMU (i.e. emulated+PV path)
and the rest have LIBXL_NIC_TYPE_VIF (i.e. PV only).

> BTW the reason for the failure seems to be that QEMU runs out of ram
> (xen: failed to populate ram at 80110000, so
> xc_domain_populate_physmap_exact failed) allocating roms for the rtl8139
> (40000 bytes each). Maybe qemu-trad wasn't loading any roms for rtl8139.
> Interestingly e1000 doesn't need any roms either, so another way around
> this would be to set 'type=e1000' for all the vifs.

Or to use the new option in 4.5 to increase the MMIO space (or is that
not where ROMs end up?)

Do we need to plumb through qemu's optionrom parameter to allow a)
limiting the number of NICs which will try to do PXE and b) allow custom
roms etc?

Ian.