From 72fa3909cfabe8822e2b8709e5d324008f55022a Mon Sep 17 00:00:00 2001

From: Jean Delvare <jdelvare@suse.de>

Date: Tue, 29 Jan 2019 14:11:42 +0100

Subject: [PATCH 07/18] dmidecode: Document how the UUID fields are interpreted

There has always been a lot of confusion about the byte order of UUID

fields. While dmidecode is doing "the right thing", documenting it

can't hurt.

This should address bug #55510:

https://savannah.nongnu.org/bugs/index.php?55510

Signed-off-by: Jean Delvare <jdelvare@suse.de>

---

 man/dmidecode.8 | 14 ++++++++++++++

 1 file changed, 14 insertions(+)

diff --git a/man/dmidecode.8 b/man/dmidecode.8

index 33f7d33..52100a8 100644

--- a/man/dmidecode.8

+++ b/man/dmidecode.8

@@ -256,6 +256,20 @@ It is crafted to hard-code the table address at offset 0x20.

 .IP \(bu "\w'\(bu'u+1n"

 The DMI table is located at offset 0x20.

+.SH UUID FORMAT

+There is some ambiguity about how to interpret the UUID fields prior to SMBIOS

+specification version 2.6. There was no mention of byte swapping, and RFC 4122

+says that no byte swapping should be applied by default. However, SMBIOS

+specification version 2.6 (and later) explicitly states that the first 3 fields

+of the UUID should be read as little-endian numbers (byte-swapped).

+Furthermore, it implies that the same was already true for older versions of

+the specification, even though it was not mentioned. In practice, many hardware

+vendors were not byte-swapping the UUID. So, in order to preserve

+compatibility, it was decided to interpret the UUID fields according to RFC

+4122 (no byte swapping) when the SMBIOS version is older than 2.6, and to

+interpret the first 3 fields as little-endian (byte-swapped) when the SMBIOS

+version is 2.6 or later. The Linux kernel follows the same logic.

+

 .SH FILES

 .I /dev/mem

 .br

-- 

2.24.0