[Bug 1551419] Re: Fix UUID endianness patch breaks cloud-init on Azure

[Dan Watkins]

OK, so I've done a bit of digging.

As of SMBIOS 2.6 (released in 2008), the first three fields of the UUID
are well-defined as being encoded in little-endian. Before that, they
could be encoded in "network byte order" (i.e. big-endian) if people
felt like it.

Presumably enough people did feel like it, as dmidecode specifically has
different code paths for pre-2.6 and post-2.6 SMBIOS versions; it will
decode pre-2.6 UUIDs as big-endian and post-2.6 UUIDs as little-endian.
(The comment in the dmidecode source code at [0] explains this pretty
well.)

And, you've guessed it, Azure reports a pre-2.6 version of SMBIOS. (To
be precise, 2.3, which was released in _1999_; Azure is old skool cool).
This explains the difference between the kernel-reported UUID (always
little-endian) and the dmidecode-reported UUID (big-endian on Azure, but
little-endian on most modern systems).

[0] https://github.com/mirror/dmidecode/blob/master/dmidecode.c#L415

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Title:
  Fix UUID endianness patch breaks cloud-init on Azure

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