linux-kernel - Re: [PATCH 2/9] uuid: use random32_get

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Date:	Wed, 31 Oct 2012 09:35:37 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	chris.mason@...ionio.com, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH 2/9] uuid: use random32_get_bytes()

On Tue, 2012-10-30 at 00:48 -0400, Theodore Ts'o wrote:
> On Tue, Oct 30, 2012 at 09:49:58AM +0800, Huang Ying wrote:
> > The uuid_le/be_gen() in lib/uuid.c has set UUID variants to be DCE,
> > that is done in __uuid_gen_common() with "b[8] = (b[8] & 0x3F) | 0x80".
> 
> Oh, I see, I missed that.
> 
> > To deal with random number generation issue, how about use
> > get_random_bytes() in __uuid_gen_common()?
> 
> We already have generate_random_uuid() in drivers/char/random.c, and
> no users for lib/uuid.c's equivalent uuid_be_gen().  So here's a
> counter-proposal, why don't we drop lib/uuid.c, and include in
> drivers/char/random.c:
> 
> /*
>  * Generate random GUID
>  *
>  * GUID's is like UUID's, but they uses the non-standard little-endian
>  * layout, compared to what is defined in RFC-4112; it is primarily
>  * used by the EFI specification.
>  */
> void generate_random_guid(unsigned char uuid_out[16])
> {
> 	get_random_bytes(uuid_out, 16);
> 	/* Set UUID version to 4 --- truly random generation */
> 	uuid_out[7] = (uuid_out[7] & 0x0F) | 0x40;
> 	/* Set the UUID variant to DCE */
> 	uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
> }
> EXPORT_SYMBOL(generate_random_guid);
> 
> I really don't think it's worth it to have a __uuid_gen_common once we
> are using get_random_bytes(), since there isn't much code to be
> factored out, and it's simpler just to have two functions in one place.

The intention of lib/uuid.c is to unify various UUID related code, and
put them in same place.  In addition to UUID generation, it provide some
other utility and may provide/collect more in the future.  So do you
think it is a good idea to put generate_rand_uuid/guid into lib/uuid.c
and maybe change the name/prototype to make it consistent with other
uuid definitions?

> Using UUID vs. GUID I think makes things much clearer, since the EFI
> specification talks about GUID's, not UUID's, and that way we don't
> have to worry about people getting confused about whether they should
> be using the little-endian versus big-endian variant.  (And I'd love
> to ask to whoever wrote the EFI specification what on *Earth* were
> they thinking when they decided to diverge from the rest of the
> world....)

I think that is a good idea.  From Wikipedia, GUID is in native byte
order, while UUID is in internet byte order.

Best Regards,
Huang Ying


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