[U-Boot] [PATCH v4 3/6] lib: uuid: add functions to generate UUID version 4

[Stephen Warren <swarren@wwwdotorg.org>]

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.