I'm playing around with rewriting efibootmgr, and I want it to use
libblkid to figure out how to label disks. Unfortunately, there's a
bit of byte order confusion. libblkid treats gpt guids like they're
big-endian, which seems to contradict the spec and all other software.
gpt.c does:
blkid_partition_set_uuid(par,
(const unsigned char *) &e->unique_partition_guid);
blkid_partition_set_type_uuid(par,
(const unsigned char *) &e->partition_type_guid);
which assumes that the guids are stored in big-endian (i.e. sane) byte order.
Unfortunately, the rest of the world seems to disagree.
- The UEFI 2.3 spec says (section 1.8.1) "the low-order byte of a
multibyte data item in memory is at the lowest address" and section
6.3 says:
typedef struct {
UINT32 Data1;
UINT16 Data2;
UINT16 Data3;
UINT8
Data4[8];
} EFI_GUID;
This means that the the first three fields should be byte-swapped.
Wikipedia's page on GPT agrees.
Finally, blkid seems to be alone among the standard tools in its interpretation:
# sgdisk -i 1 /dev/sda
Partition GUID code: C12A7328-F81F-11D2-BA4B-00A0C93EC93B (EFI System)
Partition unique GUID: 61FAE219-E1B7-492F-A147-5FAA268BECBF
[...]
# efibootmgr -v
[...]
Boot0000* Linux HD(1,800,80000,61fae219-e1b7-492f-a147-5faa268becbf)File(\EFI\redhat\grub.efi)
[...]
# blkid -p /dev/sda1 -i
[...]
PART_ENTRY_SCHEME=gpt
PART_ENTRY_UUID=19e2fa61-b7e1-2f49-a147-5faa268becbf
PART_ENTRY_TYPE=28732ac1-1ff8-d211-ba4b-00a0c93ec93b
UEFI spec 2.3 section 5.3 gives the EFI system partition guid as
"C12A7328-F81F-11D2-BA4B-00A0C93EC93B", which agrees with the little
endian order.
Should I submit a patch to fix up the byte order? I don't think that
fixing this will break anyone's boot since findfs and friends seem to
use UUID not PART_ENTRY_UUID.
(I think we should at least fix PART_ENTRY_TYPE -- anyone who looks up
the types in a table will get confused.)
--Andy
--
To unsubscribe from this list: send the line "unsubscribe util-linux" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
