[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).

Why?

> 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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