Re: [Xen-API] [xen-api-libs.hg:PATCH 0 of 2] Uuid stuff.

[Magnus Therning <magnus.therning@xxxxxxxxxxxxx>]

On 30/07/10 02:49, Todd Deshane wrote:
> On Thu, Jul 29, 2010 at 11:46 AM,  <magnus.therning@xxxxxxxxxxxxx> wrote:
>> Is this a direction that's worthwhile to pursue?
>> Would a make_uuid_urandom also be necessary?  (E.g. getting session
>> UUIDs from /dev/random might be too heavy weight for something that's
>> that short-lived.)
> 
> Would it be possible to use uuidgen for something that simple?
> 
> http://linux.die.net/man/1/uuidgen

Yes, it would, but I'm not sure that it'd simplify things that much.
Currently the code reads a few bytes from a device and then converts them into
a string of the appropriate format.  Using uuidgen would require spawning a
process on each UUID creation, and reading its stdout.  Given how frequently
xapi generates UUIDs I'd guess that this would cause a performance hit.

The issue at hand is that xapi uses entropy very liberally, and entropy is a
dear resource in dom0.  So it makes sense to try to conserve it a bit,
especially when noticing that UUIDs are used for so many things.  Splitting it
into three groups seems useful to me:

 1. UUIDs that are long-lived secrets (e.g. pool secret)
 2. UUIDs that identify objects, but in reality are short-lived secrets (e.g.
    sessions)
 3. UUIDs that identify objects (e.g. PBDs, VDIs, etc)

So, my initial thought was the following:

 1. Use UUIDs generated from /dev/random
 2. Use UUIDs generated from /dev/urandom
 3. Use UUIDs generated from OCaml's Random

Cheers,
M

-- 
Magnus Therning
magnus.therning@xxxxxxxxxxxxx          Jabber: magnusth@eng

There does not now, nor will there ever, exist a programming language
in which it is the least bit hard to write bad programs.
     -- Flon's Axiom

_______________________________________________
xen-api mailing list
xen-api@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/mailman/listinfo/xen-api