domblkinfo->allocation is not equals to domstats.1->allocation for disk with <slices> settings

[Zhen Tang <zhetang@xxxxxxxxxx>]

Hi,

I did some testing about disk with <slice> setting and found that the value of domblkinfo->allocation is not same with domstats.1->allocation for disk with <slices>

Env:

libvirt-8.0.0-4.el9

qemu-kvm-6.2.0-9.el9

Step:

1. prepare a image 

# qemu-img create /car/lib/libvirt/images/disk-raw -f raw 100M -o preallocation=full

2. start a guest and attach the disk

➜  ~ cat disk.xml
<disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native' copy_on_read='off' discard='ignore' detect_zeroes='on'/>
      <source file='/var/lib/libvirt/images/disk-raw' index='1'>
        <slices>
          <slice type='storage' offset='0' size='104857600'/>
        </slices>
      </source>
      <backingStore/>
      <target dev='sdb' bus='scsi'/>
      <iotune>
        <total_bytes_sec>10000000</total_bytes_sec>
        <group_name>slice</group_name>
      </iotune>
      <alias name='ua-slices'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>

3. Write some data to the slices disk in vm

(in vm) dd if=/dev/zero of=/dev/sdb bs=10M count=1

4. check domblkinfo and domstats

➜  ~ virsh domstats rhel9.0-1 --block|grep -Ei 'block.1.(allocation|capacity|physical)'
  block.1.allocation=0
  block.1.capacity=104857600
  block.1.physical=104865792
➜  ~
➜  ~ virsh domblkinfo rhel9.0-1 sdb|grep -Ei '(allocation|capacity|physical)'
Capacity:       104857600
Allocation:     104865792
Physical:       104857600

Are these 'allocation' values expected to be equal to each other? 

Thanks,

Zhen Tang