The calculation whether to resize the partition only works with disks
with 512 byte sector size. Use values provided by sfdisk exclusively to
make sure comparing the same sector size.
Furthermore, it seems that sgdisk does not like sfdisk's backup GPT
placement:
$ sgdisk -e /dev/zram1
Warning! Secondary partition table overlaps the last partition by 250 blocks!
Today it seems sfdisk can handle GPT quite well. Use sfdisk for all
operations in hassos-expand.
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