[dm-crypt] LUKS GPT GUID

Karel Zak kzak at redhat.com
Mon Jan 27 10:53:53 CET 2014

On Sun, Jan 26, 2014 at 10:24:39AM +0100, Milan Broz wrote:
> On 01/26/2014 02:40 AM, Pali Rohár wrote:
> > Hello,
> > 
> > according to wikipedia [1] and other sites (e.g. [2]) MBR partition ID
> > for LUKS is E8. I tried to find GPT partition GUID for LUKS, but there
> > is nothing on wikipedia [3] nor google... So has LUKS already

Frankly, who cares about partition types? 

IMHO partition types make sense in firmwares like UEFI to detect boot
partition (e.g. GPT system partition) or in special cases when you
want to mark a partition for a special purpose (e.g. /home).

It's bad idea to use partition types for something else, especially
add to the partition table info about partition format (e.g. E8 for
LUKS).  It's nightmare to maintain something like this and I'm sure
that we don't want to maintain mkfs-like programs that modify
partition tables.

> > preferred/assigned GUID for GPT partition table? There is already GPT
> > GUID for linux data, raid, swap, lvm and home partitions (see [3]), so
> > I think that LUKS should have GUID too.

All these are historical mistakes, I have doubts we want to contribute
to this nonsense.

BTW, do you know what is the "official" list of the partition types
for MBR according to UEFI standard? It's Brouwer's (~aeb) web page [2]. 

IMHO it's pretty absurd situation when official standards have to link 
random hobby web pages on Internet, because there is no official
authority that main such list... I think it obvious proof that
partition types for things like LIKS, swap, ... is unofficial junk.

> this is wonderful... who assigned E8 type? I thought LUKS has no assigned
> partition type and also I doubt LVM2 type is properly assigned too
> (it is probably form the LVM1 age when it was implemented in-kernel directly
> and partition type was important to detect it.) But not sure about this.
> Anyway, today partition type is ignored (both in LVM and LUKS), so it is really
> just for convenience for other applications.
> (Anyway, code should always use (lib)blkid to detect what's really on the device,
> not trust partition id.)
> For GPT GUID, I would like to know how these GUID codes appeared in libfdisk
> and how this was standardized for LVM. LUKS should have GUID too then...
> (cc to Karel as util-linux/libfdisk maintainer ;-)

As Rod for gfdisk, wikipedia is the first source, and then random
requests from community.

> > [2] - http://www.win.tue.nl/~aeb/partitions/partition_types-1.html


 Karel Zak  <kzak at redhat.com>

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