On Mon, Feb 28, 2011 at 11:27:34PM -0500, Andrew Lutomirski wrote:
> 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.
.. because UUID is according to all standards 16 byte array, except
Intel EFI standard...
> This means that the the first three fields should be byte-swapped.
> Wikipedia's page on GPT agrees.
Yes, you're right. Good catch.
> 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.
Fixed in master branch, see the patch below (it's based on GNU parted).
Thanks!
Karel
>From c2ec2ff9a2e85c6146ab9253a61a158d8aee8edc Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@xxxxxxxxxx>
Date: Tue, 1 Mar 2011 10:01:21 +0100
Subject: [PATCH] libblkid: fix EFI GPT uuid byte order
Intel uses little-endians for UUID, the rest of the sane world uses 16
byte big-endian array...
Reported-by: Andrew Lutomirski <luto@xxxxxxx>
Signed-off-by: Karel Zak <kzak@xxxxxxxxxx>
---
shlibs/blkid/src/partitions/gpt.c | 34 +++++++++++++++++++++++-----------
1 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/shlibs/blkid/src/partitions/gpt.c b/shlibs/blkid/src/partitions/gpt.c
index 8259c2f..7df17bb 100644
--- a/shlibs/blkid/src/partitions/gpt.c
+++ b/shlibs/blkid/src/partitions/gpt.c
@@ -32,20 +32,18 @@ typedef uint16_t efi_char16_t;
/* UUID */
typedef struct {
- uint8_t b[16];
+ uint32_t time_low;
+ uint16_t time_mid;
+ uint16_t time_hi_and_version;
+ uint8_t clock_seq_hi;
+ uint8_t clock_seq_low;
+ uint8_t node[6];
} efi_guid_t;
-#define EFI_GUID(a,b,c,d0,d1,d2,d3,d4,d5,d6,d7) ((efi_guid_t) \
- {{ \
- (a) & 0xff, ((a) >> 8) & 0xff, ((a) >> 16) & 0xff, ((a) >> 24) & 0xff, \
- (b) & 0xff, ((b) >> 8) & 0xff, \
- (c) & 0xff, ((c) >> 8) & 0xff, \
- (d0), (d1), (d2), (d3), (d4), (d5), (d6), (d7) \
-}})
-
-#define GPT_UNUSED_ENTRY_GUID EFI_GUID(0x00000000, 0x0000, 0x0000, 0x00, 0x00, \
- 0x00, 0x00, 0x00, 0x00, 0x00, 0x00)
+#define GPT_UNUSED_ENTRY_GUID \
+ ((efi_guid_t) { 0x00000000, 0x0000, 0x0000, 0x00, 0x00, \
+ { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }})
struct gpt_header {
uint64_t signature; /* "EFI PART" */
uint32_t revision;
@@ -120,6 +118,17 @@ static inline int guidcmp(efi_guid_t left, efi_guid_t right)
return memcmp(&left, &right, sizeof (efi_guid_t));
}
+/*
+ * UUID is traditionaly 16 byte big-endian array, except Intel EFI
+ * specification where the UUID is a structure of little-endian fields.
+ */
+static void swap_efi_guid(efi_guid_t *uid)
+{
+ uid->time_low = swab32(uid->time_low);
+ uid->time_mid = swab16(uid->time_mid);
+ uid->time_hi_and_version = swab16(uid->time_hi_and_version);
+}
+
static int last_lba(blkid_probe pr, uint64_t *lba)
{
blkid_loff_t sz = blkid_probe_get_size(pr);
@@ -352,6 +361,9 @@ static int probe_gpt_pt(blkid_probe pr, const struct blkid_idmag *mag)
(unsigned char *) e->partition_name,
sizeof(e->partition_name), BLKID_ENC_UTF16LE);
+ swap_efi_guid(&e->unique_partition_guid);
+ swap_efi_guid(&e->partition_type_guid);
+
blkid_partition_set_uuid(par,
(const unsigned char *) &e->unique_partition_guid);
--
1.7.3.4
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