Description of problem:
Boot up a guest with one qcow2 disk image(acts as one data disk), then using QMP ‘human-monitor-command’ to execute  HMP block_resize, which attempts to resize the block disk to a smaller size(e.g. 1G-->512M).
This is expected to fail, but QMP returns “success” and the block disk’s size is not correct after changing.


Version-Release number of selected component (if applicable):
Host:  kernel: 4.11.0-10.el7a.ppc64le
       qemu-kvm-2.9.0-16.el7a.ppc64le
Guest: 4.11.0-10.el7a.ppc64le

How reproducible: 100%


Steps to Reproduce:
1. boot guest with QMP enabled, Qemu cli:
/usr/libexec/qemu-kvm \
-name yilzhang_vm \
-serial unix:/tmp/myserial.log,server,nowait \
-smp 8,sockets=2,cores=4,threads=1 -m 8192 \
-qmp tcp:0:9999,server,nowait \
-monitor stdio \
-nodefaults -enable-kvm \
\
-device virtio-scsi-pci,bus=pci.0,addr=0x3,id=scsi0 \
-drive file=/home/yilzhang/rhel7.4-alt-20170626.4.qcow2,if=none,id=drive-system-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop \
-device scsi-hd,bus=scsi0.0,drive=drive-system-disk,id=system-disk,bootindex=1 \
\
-drive file=/dev/sdb3,if=none,cache=none,id=data-disk1,format=qcow2 \
-device virtio-blk-pci,drive=data-disk1,bus=pci.0,id=blk-disk1 \
\
-netdev tap,id=hostnet0,vhost=on,script=/etc/qemu-ifup \
-device virtio-net-pci,netdev=hostnet0,id=virtio-net-pci0,mac=52:54:00:c3:e7:84,bus=pci.0,addr=0x4,ioeventfd=off \
2. from any box with telnet client run #telnet $HostIP 4444
   {"execute": "qmp_capabilities"}
3. execute block_resize command with QMP "human-monitor-command" to shrink a block disk with qcow2 format
 {"execute":"human-monitor-command","arguments":{"command-line":"block_resize  data-disk1 536870912" }}



Actual results:
1. step3 QMP success:
{"execute":"human-monitor-command","arguments":{"command-line":"block_resize  data-disk1 536870912" }}
{"return": ""}
2. the block disk's size is changed to 512T which is not correct:
{"execute": "query-block"}
{"return": [{"io-status": "ok", "device": "drive-system-disk", .......  ......}, {"io-status": "ok", "device": "data-disk1", "locked": false, "removable": false, "inserted": {"iops_rd": 0, "detect_zeroes": "off", "image": {"virtual-size": 562949953421312, "filename": "/dev/sdb3", "cluster-size": 65536, "format": "qcow2", "actual-size": 0, "format-specific": {"type": "qcow2"

[guest]#   fdisk -l  /dev/vda
Disk /dev/vda: 562950.0 GB, 562949953421312 bytes, 1099511627776 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

[guest]#  lsblk -p| grep vda
/dev/vda                    252:0    0  512T  0 disk 



Expected results:
1. step3 QMP should prompt error, like:
{"error": {"class": "GenericError", "desc": "Failed to resize image: Operation not supported"}}
2. the block disk's size is NOT changed


Additional info:
If I use QMP block_resize to shrink the block image's size, QMP will prompt error message (this is expected since qcow2 image doesn't support shrink):

{ "execute": "block_resize", "arguments": { "device": "data-disk1", "size": 536870912 }}
{"error": {"class": "GenericError", "desc": "Failed to resize image: Operation not supported"}}