dumping hybrid MBR/GPT disks is fine, which can sometimes be found
on USB sticks. but prohibit editing.
however, always barf on disks with dos partitions and missing
protecive MBR partition entry.
usually, the plan9 partition table is contained in
the first 9fat partition after the pbs/fat header,
but when no 9fat partition is requested, we have
to make sure partitions wont overlap the partition
table (start at sector offset >= 2).
the shared command language assumed 512 byte sectors, which is
not the case for fdisk as it uses cylinders for the block unit.
so we introduce an extra argument in the Edit structure and
parseexpr() function so byte sizes are properly converted to
the block unit when the K,M,G and T postfixes are used.
there where two problems with blank (-b flag):
we did not update the backup header when there was already a valid
backup header in place. we always want to initialize a new backup header
in blank mode!
we now also check the backup header matches the primary (or the other
way arround depending on which header could be read), reporting any
mismatches and restoring the backup from the data of the primary.
the protective mbr needs to start at sector 1 not 0 (apparently, this
matters for ovmf).
efi systems may use traditional dos partition table
with an esp (efi system partition). otherwise, honor
the protective mbr partition (0xEE) and exit when we
encounter it.
- make UU() shorter by using long long constant to encode node field
- store Flag as a mask, not as a shift count
- put the attributes before the name in cmdsum() as it is fixed length
