[Sheepdog] [PATCH] sheep: use hash value for vdi attribute object id

[Chris Webb]

MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp> writes:

> At Wed, 3 Aug 2011 13:50:32 +0100,
> Chris Webb wrote:
> > 
> > MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp> writes:
> > 
> > > Sheepdog also uses a hash value of the vdi name to look up vdi
> > > objects, so it is already difficult to implement vdi rename simply,
> > > but I think it is not impossible.  For example, if we log all the vdi
> > > rename operations, we can traverse the renamed vdi name and get the
> > > correct hash value based on the old vdi name.
> > 
> > Or perhaps make the vdi 'name' an internal uniquely allocated 'id' value and
> > the displayed name be an attribute of the vdi? (This is what I'm already
> > doing with sheepdog in our system, as I want to be able to guarantee unique
> > 'names'.)
> 
> Let me clarify some points.
> 
> In this approach, when we rename a vdi, we specify the vdi 'id' and
> change the attribute of the vdi, yes?
> 
> What is specified in the qemu command line option as a Sheepdog volume
> name?  Is it vdi 'name' (an attribute of the vdi) or vdi 'id' (the 32
> bit integer)?

I was imagining that the vdi was internally addressed by its 'id' and the
name was just an attribute for user convenience, a bit like we fundamentally
identify snapshots by their vid but might one day give them a convenience
tag name as qcow2 snapshots have. I'm already using the vdi 'name' in this
way inside our management system, allocating a unique value to it rather
than setting it to the user-provided drive name.

Cheers,

Chris.