This value is u32 on disk, but assigned to an int in memory. After we do the
implicit conversion via assignment, check that the result is at least one[1]
(non-negative[2]).
1. The subsequent for-loop iterates from gpt_entries minus one, down, until
reaching zero. A negative or zero initial index results in undefined signed
integer overflow.
2. It is also used to index into arrays later.
In practice, we expected non-malicious disks to contain small positive values.
Reported by: Coverity
CID: 1223202
Sponsored by: EMC / Isilon Storage Division
rounddown2 tends to produce longer lines than the original code
and when the code has a high indentation level it was not really
advantageous to do the replacement.
This tries to strike a balance between readability using the macros
and flexibility of having the expressions, so not everything is
converted.
This partitioning scheme is used in DragonFlyBSD. It is similar to
BSD disklabel, but has the following improvements:
* metadata has own dedicated place and isn't accessible through partitions;
* all offsets are 64-bit;
* supports 16 partitions by default (has reserved place for more);
* has reserved place for backup label (but not yet implemented);
* has UUIDs for partitions and partition types;
No objections from: geom
MFC after: 2 weeks
Relnotes: yes
