Comment 35 for bug 1847105

Thread 6 "rpc-worker" hit Breakpoint 4, storageBackendCreateQemuImgOpts (encinfo=0x0, opts=0x7fd1791102a0, info=0x7fd179110380) at ../../../src/storage/storage_util.c:712

(gdb) p *info
$3 = {format = 14, type = 0x7fd17ef920f0 "qcow2", inputType = 0x0, path = 0x7fd164018440 "/var/lib/libvirt/images/ubuntu20.04-l.qcow2", size_arg = 2097152, allocation = 2097152,
  encryption = false, preallocate = true, compat = 0x7fd16400deb0 "1.1", features = 0x7fd16400e170, nocow = false, backingPath = 0x0, backingFormat = 0, inputPath = 0x0,
  inputFormatStr = 0x0, inputFormat = 0, secretAlias = 0x0}

And in particular:
(gdb) p info->preallocate
$4 = true
(gdb) p info->size_arg
$5 = 2097152
(gdb) p info->allocation
$6 = 2097152

So we now have equal numbers, but not bigger.
Therefore falloc is chosen still.

I have to ping on the upstream bug if that is expected.