This patch add shrinking of the image file for qcow2. As a result, this allows
us to reduce the virtual image size and free up space on the disk without
copying the image. Image can be fragmented and shrink is done by punching holes
in the image file.
# ./qemu-img create -f qcow2 image.qcow2 4G
Formatting 'image.qcow2', fmt=qcow2 size=4294967296 encryption=off
cluster_size=65536 lazy_refcounts=off refcount_bits=16
# ./qemu-io -c "write -P 0x22 0 1G" image.qcow2
wrote 1073741824/1073741824 bytes at offset 0
1 GiB, 1 ops; 0:00:04.59 (222.886 MiB/sec and 0.2177 ops/sec)
# ./qemu-img resize image.qcow2 512M
warning: qemu-img: Shrinking an image will delete all data beyond the shrunken
image's end. Before performing such an operation, make sure there is no
important data there.
error: qemu-img: Use the --shrink option to perform a shrink operation.
# ./qemu-img resize --shrink image.qcow2 128M
Image resized.
# ./qemu-img info image.qcow2
image: image.qcow2
file format: qcow2
virtual size: 128M (134217728 bytes)
disk size: 128M
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
# du -h image.qcow2
129M image.qcow2