[dm-crypt] LUKS GPT GUID

Pali Rohár pali.rohar at gmail.com
Mon Jan 27 11:05:29 CET 2014

2014-01-27 Karel Zak <kzak at redhat.com>:
> 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.

Of course, mkfs program should not modify partition table! Editing
parittion table then it is up to system admin (if he using mkfs) or
some high level partition program.

>> > 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.

In my opinion, if partition table (e.g GPT) support specifing
partition label, uuid or partition type, why user/admin cannot use it
(at least for his own usage)? I think its up to admin, if he want to
use it or not. He can write own udev rules to export these information
to system /dev/ or not.

>> 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
> --
>  Karel Zak  <kzak at redhat.com>
>  http://karelzak.blogspot.com

Pali Rohár
pali.rohar at gmail.com

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