From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Warren <swarren@wwwdotorg.org>
Date: Wed, 26 Mar 2014 12:47:36 -0600
Subject: [U-Boot] [PATCH v4 3/6] lib: uuid: add functions to generate
 UUID version 4
In-Reply-To: <5332C172.70401@samsung.com>
References: <5ef7cdb8df4fb05c3c371e29d7a61e28e1563a68.1394807506.git.p.marczak@samsung.com>
	<1395251911-26540-1-git-send-email-p.marczak@samsung.com>
	<1395251911-26540-3-git-send-email-p.marczak@samsung.com>
	<5331D8D1.7040301@wwwdotorg.org> <5332C172.70401@samsung.com>
Message-ID: <533320C8.8030308@wwwdotorg.org>
List-Id: <u-boot.lists.denx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: u-boot@lists.denx.de

On 03/26/2014 06:00 AM, Przemyslaw Marczak wrote:
> On 03/25/2014 08:28 PM, Stephen Warren wrote:
>> On 03/19/2014 11:58 AM, Przemyslaw Marczak wrote:
>>> This patch adds support to generate UUID (Universally Unique Identifier)
>>> in version 4 based on RFC4122, which is randomly.
>>>
>>> Source: https://www.ietf.org/rfc/rfc4122.txt

>>> diff --git a/lib/uuid.c b/lib/uuid.c
>>
>>>   /*
>>>    * UUID - Universally Unique IDentifier - 128 bits unique number.
>>>    *        There are 5 versions and one variant of UUID defined by RFC4122
>>> - *        specification. Depends on version uuid number base on a time,
>>> - *        host name, MAC address or random data.
>>> + *        specification. Depends on version uuid number base on:
>>
>> I still have no idea what "Depends on version uuid number base on" means.
> 
> It means that each UUID version "result" depends on different source
> data, as listed here...

How bout replacing that sentence with:

A UUID contains a set of fields. The set varies depending on the version
of the UUID, as shown below:

>>> + *        - time, MAC address(v1),
>>> + *        - user ID(v2),
>>> + *        - MD5 of name or URL(v3),
>>> + *        - random data(v4),
>>> + *        - SHA-1 of name or URL(v5),

>>> + * timestamp - 60-bit: time_low, time_mid, time_hi_and_version
>>> + * version   - 4 bit (bit 4 through 7 of the time_hi_and_version)
>>> + * clock seq - 14 bit: clock_seq_hi_and_reserved, clock_seq_low
>>> + * variant:  - bit 6 and 7 of clock_seq_hi_and_reserved
>>> + * node      - 48 bit
>>> + * In this version all fields beside 4 bit version are randomly generated.
>>> + * source: https://www.ietf.org/rfc/rfc4122.txt
>>
>> gen_rand_uuid() doesn't actually honor that format; it creates pure
>> random data rather than filling in any timestamps, clock sequence
>> data, etc.
> 
> Actually, yes but two fields are NOT set randomly, and this is what
> comment includes:
> "In this version all fields beside 4 bit version are randomly generated."
> Moreover the gen_rand_uuid() respects endianess for setting bits,
> and this could be checked on linux host by "uuid -d uboot_uuid_string"
> in shell.

While it's true that some fields are set non-randomly, most aren't; you
really can't claim that e.g. placing random data in the timestamp field
is a valid timestamp.