How to change a block device virtual-size on a running VM?

[Ilya Yakushin]

Hello!

I'm trying to reszie a disk on a working VM using the qemu monitor.

```
# zfs set volsize=2571108352 fastpool/vm/vm-9008-disk-0
# qm monitor 9008
Entering Qemu Monitor for VM 9008 - type 'help' for help
qm> info block -v
drive-scsi0 (#block178): /dev/zvol/fastpool/vm/vm-9008-disk-0 (raw)
    Attached to:      scsi0
    Cache mode:       writeback, direct
    Detect zeroes:    on

Images:
image: /dev/zvol/fastpool/vm/vm-9008-disk-0
file format: raw
virtual size: 2.3 GiB (2466250752 bytes)
disk size: 0 B
qm> block_resize drive-scsi0 2654994432
Error: Cannot grow device files
```

As I can see, the qemu monitor sending to a socket json like this:
```
{
  "id": "2737013:2",
  "arguments": {
    "command-line": "block_resize drive-scsi0 2654994432"
  },
  "execute": "human-monitor-command"
}
```
and the socket returns back error message:
"Error: Cannot grow device files"

Maybe I should use different command in the qemu-monitor to change virtual size 
of a VM?

I'm using the Proxmox, which sending to a qemu socket different json:
{
  "id": "1889371:2",
  "arguments": {
    "size": 2571108352,
    "device": "drive-scsi0"
  },
  "execute": "block_resize"
}
This json successfully change virtual block size of a block device.

Regards,
Ilya Yakushin