Re: [Qemu-devel] [PATCHv2-RFC 0/2] RFC: standard pci bridge device

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

On Mon, Feb 13, 2012 at 05:38:26PM +0800, Wen Congyang wrote:
> At 02/13/2012 05:15 PM, Michael S. Tsirkin Wrote:
> > Here's a new version of the patch. It works for me.
> > Deep nesting of bridges is supported.
> > You need a small BIOS patch to support the OSHP method
> > if you want hotplug to work. I will post this separately.
> > We'd need a full ACPI driver to make hotplug work for guests
> > without an SHPC driver (e.g. windows XP).
> > Management support will also be needed.
> > 
> > One small wrinkle is that the pci_addr property
> > wants data in a format bus:device.function which is
> > broken as guests can change bus numbers.
> > For testing I used the 'addr' property which
> > encodes slot*8+function#. We probably want to
> > extend pci_addr in some way (e.g. :device.function ?
> > Thoughts?).
> 
> What about using id+device(slot)+function to set the address?

That's exactly what this patch does: addr encodes
slot+function.
I was asking about a friendlier format for this.

> > 
> > The SHPC controller supports up to 31 devices
> > (out of 32 slots) so slot 0 doesn't support hotplug.
> > Non hot-pluggable devices behind the bridge
> > don't work currectly (we'll try to unplug them)
> > so don't do this.
> > For now I just blocked adding devices in slot 0,
> > in the future it might be possible to add
> > a non-hotpluggable device there.
> > 
> > Example:
> > 
> > qemu-system-x86_64  -enable-kvm -m 1G
> >  -drive file=/home/mst/rhel6.qcow2
> > -netdev
> > tap,id=foo,ifname=msttap0,script=/home/mst/ifup,downscript=no,vhost=on
> > -device pci-bridge,id=bog
> > -device virtio-net-pci,netdev=foo,bus=bog,addr=8
> > 
> > 
> > Hot-unplug currently causes qemu to crash, this
> > happens without this patch too, so I'm not worried :)
> 
> How to trigger this bug without this patch?
> 
> Thanks
> Wen Congyang

start with 
 qemu-system-x86_64  -enable-kvm -m 1G
  -drive file=/home/mst/rhel6.qcow2
 -netdev
 tap,id=foo,ifname=msttap0,script=/home/mst/ifup,downscript=no,vhost=on

next do:
device_add virtio-net-pci,netdev=foo,id=bla
<wait a bit for guest to notice the device>
device_del bla
<wait for device to go away>
and it will crash on next malloc, to trigger
malloc give another command, e.g.
info pci

> > 
> > New since v1:
> > 	hotplug support
> >