[libvirt-users] virt-sparsify changing the apparent-size of files

[libvirt_users at skagitattic.com]

Hello, 

I am curious why when using virt-sparsify the apparent-size of the file
gets reduced to the actual file size?  Is there a way to get the
apparent-size left as the full size?

In the man page for virt-sparsify it has a section on
"IMPORTANT NOTE ABOUT SPARSE OUTPUT IMAGES" and its output seems to
indicate what I would expect where "ls -lh" shows the full apparent size
and "du -sh" shows the actual size.  But my actual results from testing
are different.

In the following example input.qcow2 is before sparsify and output.qcow2
is after.

Doing ls reports full size for input but a small size for
the output:
root at testingbox:/tmp/test # ls -lh
total 3.1G
-rw-r--r-- 1 root root 512M Jun 14 22:30 file.img
-rw-r--r-- 1 root root  51G Jun 14 22:30 input.qcow2
-rw-r--r-- 1 root root 790M Jun 14 22:36 output.qcow2

Same when asking du for apparent-size:
root at testingbox:/tmp/test # du -h --apparent-size *
512M    file.img
51G     input.qcow2
790M    output.qcow2

A normal du will show the actual size of the files:
root at testingbox:/tmp/test # du -h *
0       file.img
2.4G    input.qcow2
790M    output.qcow2

The only way I have found to check the full virtual size of the file
after virt-sparsify is with qemu-img:
root at testingbox:/tmp/test # qemu-img info input.qcow2
image: input.qcow2
file format: qcow2
virtual size: 50G (53687091200 bytes)
disk size: 2.3G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
root at testingbox:/tmp/test # qemu-img info output.qcow2
image: output.qcow2
file format: qcow2
virtual size: 50G (53687091200 bytes)
disk size: 789M
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false


Thanks!