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From e1dfe0aec7bf2bc7f906f65ca1d5c82bd23d8f33 Mon Sep 17 00:00:00 2001
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From: Jean Delvare <jdelvare@suse.de>
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Date: Tue, 29 Jan 2019 14:11:42 +0100
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Subject: [PATCH 02/11] dmidecode: Document how the UUID fields are interpreted
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There has always been a lot of confusion about the byte order of UUID
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fields. While dmidecode is doing "the right thing", documenting it
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can't hurt.
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This should address bug #55510:
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https://savannah.nongnu.org/bugs/index.php?55510
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Signed-off-by: Jean Delvare <jdelvare@suse.de>
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---
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man/dmidecode.8 | 14 ++++++++++++++
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1 file changed, 14 insertions(+)
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diff --git a/man/dmidecode.8 b/man/dmidecode.8
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index 33f7d33bd5ef..52100a82435e 100644
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--- a/man/dmidecode.8
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+++ b/man/dmidecode.8
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@@ -256,6 +256,20 @@ It is crafted to hard-code the table address at offset 0x20.
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.IP \(bu "\w'\(bu'u+1n"
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The DMI table is located at offset 0x20.
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+.SH UUID FORMAT
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+There is some ambiguity about how to interpret the UUID fields prior to SMBIOS
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+specification version 2.6. There was no mention of byte swapping, and RFC 4122
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+says that no byte swapping should be applied by default. However, SMBIOS
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+specification version 2.6 (and later) explicitly states that the first 3 fields
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+of the UUID should be read as little-endian numbers (byte-swapped).
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+Furthermore, it implies that the same was already true for older versions of
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+the specification, even though it was not mentioned. In practice, many hardware
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+vendors were not byte-swapping the UUID. So, in order to preserve
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+compatibility, it was decided to interpret the UUID fields according to RFC
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+4122 (no byte swapping) when the SMBIOS version is older than 2.6, and to
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+interpret the first 3 fields as little-endian (byte-swapped) when the SMBIOS
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+version is 2.6 or later. The Linux kernel follows the same logic.
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+
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.SH FILES
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.I /dev/mem
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.br
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--
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2.17.1
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