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

[Max Reitz]

But that’s the point of that field, to show the amount of space used by
the image on the host.

The man page documents it as: “disk size: How much space the image file
occupies on the host file system (may be shown as 0 if this information
is unavailable, e.g. because there is no file system)”, and the QAPI
definition of ImageInfo documents the actual-size field as “actual size
on disk in bytes of the image”.

So it is documented as and intended to be the number of bytes used, not
the length of the file.

Max

** Changed in: qemu
       Status: New => Invalid

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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:
  Invalid

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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