[Parted-maintainers] Bug#1025223: parted: limited to 128 GPT partitions

[Pascal Hambourg]

On Thu, 01 Dec 2022 18:58:08 +1100 Trent W. Buck wrote:
> 
> But parted seems to be limited to 128 GPT partitions (test transcript below).
> Is this a fundamental limitation of GPT?

No. AFAIK the GPT specification only says that a minimum of 16384 bytes 
of space must be reserved for the GPT partition entry array and the 
minimum partition entry size is 128 bytes. These minimum sizes allow 
16384 / 128 = 128 partition entries, which is considered a safe default 
and should be supported by any software or device.

Other tools such as gdisk allow to change the partition table size. 
Parted creates GPT partition tables with 128 entries but can read and 
write existing partition tables with less or more entries.

> If not, can parted be changed to allow 256 partitions?

I can think of three options:

- Set the new partition table size at build time.
IMO neither parted nor Debian maintainers would accept to change the new 
partition table size in order to preserve compatibility. But of course 
you can rebuild your own parted flavour with a custom size.

- Set the new partition table size at run time.
This could be implemented with an environment variable, like 
PARTED_SECTOR_SIZE which defines the sector size when working on disk 
image files.

- Implement a partition table size change feature.
Parted uses the same generic API for all partition table types, and 
AFAIK the currently only available interface for partition table 
settings is disk flags (e.g. pmbr_boot which reflects the state of the 
boot flag in the protective MBR). But even if they are internally stored 
as integers, disk flags are managed as on/off boolean values, not 
numbers. A new disk flag could reflect that the partition table has 128 
or 256 entries, but how to reflect all other values ?

Anyway feature requests should be asked to parted upstream, not Debian.