[Qemu-devel] Re: [PATCH] new parameter boot=on|off for "-net nic" and "-device" NIC devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 21, 2010 at 04:18:56PM +0200, Bernhard Kohl wrote:
> Am 19.09.2010 18:07, schrieb ext Michael S. Tsirkin:
> >On Tue, Sep 14, 2010 at 05:46:55PM +0200, Bernhard Kohl wrote:
> >>>  This patch was motivated by the following use case: In our system
> >>>  the VMs usually have 4 NICs, any combination of virtio-net-pci and
> >>>  pci-assign NIC devices. The VMs boot via gPXE preferably over the
> >>>  pci-assign devices.
> >>>  >  There is no way to make this working with a combination of
> >>the
> >>>  current options -net -pcidevice -device -optionrom -boot.
> >>>  >  With the parameter boot=off it is possible to avoid
> >>loading
> >>>  and using gPXE option ROMs either for old style "-net nic" or
> >>>  for "-device" NIC devices. So we can select which NIC is used
> >>>  for booting.
> >>>  >  A side effect of the boot=off parameter is that unneeded
> >>ROMs
> >>>  which might waste memory are not longer loaded. E.g. if you have
> >>>  2 virtio-net-pci and 2 pci-assign NICs in sum 4 option ROMs are
> >>>  loaded and the virtio ROMs take precedence over the pci-assign
> >>>  ROMs. The BIOS uses the first gPXE ROM which it finds and only
> >>>  needs one of them even if there are more NICs of the same type.
> >>>  >  Without using the boot=on|off parameter the current
> >>behaviour
> >>>  does not change.
> >>>  >  Signed-off-by: Thomas Ostler<thomas.ostler@nsn.com>
> >>>  Signed-off-by: Bernhard Kohl<bernhard.kohl@nsn.com>
> >I think this is useful, however:
> >
> >- We have bit properties which handle parsing on/off
> >   and other formats automatically. Please don't use string.
> >- boot is not a great property name for PCI: what
> >   you actually do is disable option rom.
> >   So maybe call it 'rom' or something like that?
> Our main goal is to select a certain NIC's option rom for booting.
> So the other roms are not needed and not loaded. We used 'boot'
> as the property name as it is similar as in the '-drive' option to
> select a certain disk for booting. What's about to call it 'bootrom'?

Sounds good.

> >- given you have added a property, it can now
> >   be changed with -device. and visible in -device ?
> >   This also has an advantage of only applying to pci devices
> >   (-net option would appear to apply to non-pci but have no effect).
> >   Please do not add more flag parsing in qdemu-options, net and vl.c
> I think it is OK that we don't support this new feature for the old
> style '-net' option and only implement it for qdev / -device?


I think so, too.

> >To summarize, just add a qdev bit option and check
> >the bit.
> >
> In general, we will rework the patch and use all new qdev features.
> There are also some memory leaks as Chris told us, because of the
> usage of strdup.
> 
> This rework might take 2 weeks because of vacation.
> 
> Thanks
> Bernhard

Sounds good.

-- 
MST