Description of problem:
After hot add a spapr-vscsi hard disk, it could not be detected inside the guest; but after reboot the guest, it can be detected and used

Version-Release number of selected component (if applicable):
Host kernel: 3.10.53-2020.1.pkvm2_1_1.49.ppc64
Guest kernel: 3.10.0-227.el7.ppc64/3.10.0-223.ael7b.ppc64le

How reproducible:
100%

Steps to Reproduce:
1. Start a guest as follows with 2 spapr-vscsi controller:

/usr/bin/qemu-system-ppc64 -name spaprqcow-0205 -machine pseries-2.2,accel=kvm,usb=off -m 32768 -smp 4,sockets=1,cores=4,threads=2 -realtime mlock=off -uuid 95346a10-1828-403a-a610-ac5a52a29442 -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/spaprqcow-0205.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,clock=host -no-shutdown -boot strict=on -device nec-usb-xhci,id=xhci -device spapr-vscsi,id=scsi0,reg=0x1000 -device spapr-vscsi,id=scsi1,reg=0x6000 -drive file=/media/nfs/spaprqcow-0205,if=none,id=drive-scsi0-0-0-0,format=qcow2,cache=none -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1 -drive file=/media/ngu-nfs/iso/RHEL-7.1-20150129.0-Server-ppc64-dvd1.iso,if=none,id=drive-scsi0-0-1-0,readonly=on,format=raw,cache=none -device scsi-cd,bus=scsi0.0,channel=0,scsi-id=1,lun=0,drive=drive-scsi0-0-1-0,id=scsi0-0-1-0,bootindex=2 -netdev tap,id=hostnet0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown -device spapr-vlan,netdev=hostnet0,id=net0,mac=52:54:00:c4:e7:42,reg=0x2000 -chardev pty,id=charserial0 -device spapr-vty,chardev=charserial0,reg=0x30000000 -device usb-kbd,id=input0 -device usb-mouse,id=input1 -device usb-tablet,id=input2 -vnc 0:02 -device VGA,id=video0,bus=pci.0,addr=0x4 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 -object rng-random,id=rng0,filename=/dev/random -device virtio-rng-pci,rng=rng0,max-bytes=1234,period=2000,bus=pci.0,addr=0x5 -msg timestamp=on

2. Connect to its qmp with cmd 'nc -U /var/lib/libvirt/qemu/spaprqcow-0205.monitor' in another host terminal
3. Issue qmp command: {"execute":"qmp_capabilities"}
4. Issue following qmp command in sequence to hot add a spapr-vscsi disk to controller 1, where there is not any disk till now:
{ "execute": "blockdev-add",
"arguments": { "options" : {
"id": "scsi1-0-0-0",
"driver": "raw",
"file": { "driver": "file",
"filename": "/media/nfs/hd-1-02132015" } } } }

{"execute":"device_add","arguments":{"driver":"scsi-hd","drive":"scsi1-0-0-0","id":"scsi1-0-0-0"}}
5. Check the new added disk with qmp cmd: {"execute":"query-block"}; and inside the guest check it with cmd 'll /dev/sd*'
6. Host add another spapr-vscsi disk to controller 0, where there are already two disks till now, as steps 4 do
7. Check the new added disk as step 5 do


Actual results:
In steps 5 and 7, the new added scsi disks could be detected from qmp cmd {"execute":"query-block"} output, but couldn't inside the guest; however, after reboot the guest, the two hot added disks were detected inside the guest

Expected results:
Hot added disks could be detected without guest system reboot

Additional info:
'ppc64-diag-2.6.7-6.el7.ppc64'/'ppc64-diag-2.6.7-6.ael7b.ppc64le' has been installed on the guest by default