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"qemu-img convert -O qcow2 -o backing_file" makes huge images
$ dd if=/dev/urandom bs=1M of=1.img count=4
4+0 records in
4+0 records out
4194304 bytes (4,2 MB) copied, 1,0413 s, 4,0 MB/s
$ qemu-img create -f qcow2 -b 1.img 2.img
Formatting '2.img', fmt=qcow2 size=4194304 backing_file='1.img' encryption=off cluster_size=0
$ qemu-img convert -O qcow2 -o backing_file=1.img 2.img 3.img
$ du -h ?.img
4,1M 1.img
144K 2.img
4,3M 3.img
The conversion result is bigger then the source!
It appears that "-o backing_file" is not applied to data (as expected). I.e. all data is put into the resulting image: both from source image and "backing" image.
Expected behavior is to put only data that is not present in backing_file.
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