[Qemu-devel] About hotplug multifunction

[Amos Kong]

Hello all,

I'm working on hotplug pci multifunction. 

1. qemu cmdline: 
./x86_64-softmmu/qemu-system-x86_64 -snapshot -m 2000 
/home/kvm_autotest_root/images/rhel61-64-virtio.qcow2 -vnc :0 -monitor 
unix:/tmp/a,server,nowait --enable-kvm -net none

2. script to add virtio-blk devices:
for i in `seq 1 7` 0;do
qemu-img create /tmp/resize$i.qcow2 1G -f qcow2
echo drive_add 0x6.$i id=drv$i,if=none,file=/tmp/resize$i.qcow2 | nc -U /tmp/a
echo device_add 
virtio-blk-pci,id=dev$i,drive=drv$i,addr=0x6.$i,multifunction=on | nc -U /tmp/a
done

3. script to add virio-nic devices:
for i in `seq 1 7` 0;do
echo netdev_add tap,id=drv$i | nc -U /tmp/a
echo device_add 
virtio-net-pci,id=dev$i,netdev=drv$i,addr=0x6.$i,multifunction=on | nc -U /tmp/a
done

4. current qemu behaviors
4.1. add func 1~7 one by one, then add func 0
virtio-nic : success, all funcs are added
virtio-blk : success

4.2. add func 0~7 one by one
virtio-nic : failed, only func 0 is added
virtio-blk : success

4.3. removing any single func in monitor
virtio-nic: func 0 are not found in 'lspci', func 1~7 also exist. eth1~eth7 
also exist.
virtio-blk: func 0 are not found in 'lspci', func 1~7 also exist. the device. 
/dev/vda disappears,
              vdb,vdc,vde,vdf,vdg,vdh,vdi,vdj also exist. If I re-add 8 funcs 
to guest, they all works.
              # lspci (00:06.1 ~ 00:06.7 exist, 00:06.0 doesn't exit)
              00:06.1 SCSI storage controller: Red Hat, Inc Virtio block device 
(rev ff)

qemu sends an acpi event to guest, then guest will remove all funcs in the slot.
linux-2.6/drivers/pci/hotplug/acpiphp_glue.c:
static int disable_device(struct acpiphp_slot *slot) {
    list_for_each_entry(func, &slot->funcs, sibling) {
        ...

Questions:
1. why func1~7 still can be found after hot-remove? is it same as real hardware?
2. why the func 1~7 could not be added to guest (addingfunc 0~7 one by one)?
3. how about this interface to hotplug/hot-unplug multifunction:
   1) Add func 1-7 by monitor, add func 0, then send an acpi event to notice 
guest
   2) Remove func0, send an acpi event to guest. (all funcs can be removed)
4. what does "reversion 0xff" stand for?

Thanks in advance,
Amos