[Bug 1881648] [NEW] `qemu-img info` reports an incorrect actual-size when the underlying posix filesystem has transparent compression

[Graham Christensen]

Public bug reported:

qemu-img info reports the same thing as `du`*1024:

$ qemu-img info --output json ./my.qcow2  | jq '."actual-size"'
558619648

$ du ./my.qcow2
545527  ./my.qcow2

$ echo $((558619648 / 545527))
1024

and this is correct in terms of bytes on disk, but due to transparent
compression implemented by the filesystem, it is not the actual byte
count:

$ du -h --apparent-size ./my.qcow2
1346568192      my.qcow2

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1881648

Title:
  `qemu-img info` reports an incorrect actual-size when the underlying
  posix filesystem has transparent compression

Status in QEMU:
  New

Bug description:
  qemu-img info reports the same thing as `du`*1024:

  $ qemu-img info --output json ./my.qcow2  | jq '."actual-size"'
  558619648

  $ du ./my.qcow2
  545527        ./my.qcow2

  $ echo $((558619648 / 545527))
  1024

  and this is correct in terms of bytes on disk, but due to transparent
  compression implemented by the filesystem, it is not the actual byte
  count:

  $ du -h --apparent-size ./my.qcow2
  1346568192    my.qcow2

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