Re: [Xen-devel] Domain Save Image Format proposal (draft B)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-02-11 at 12:09 +0000, Ian Campbell wrote:
> 
> 
> > >>
> --------------------------------------------------------------------
> > >> Field       Description
> > >> -----------
> --------------------------------------------------------
> > >> count       Number of pages described in this record.
> > >>
> > >> pfn         An array of count PFNs. Bits 63-60 contain
> > >>             the XEN\_DOMCTL\_PFINFO_* value for that PFN.
> > > 
> > > Now might be a good time to remove this intertwining? I suppose
> 60-bits
> > > is a lot of pfn's, but if the VMs address space is sparse it isn't
> out
> > > of the question.
> > 
> > I don't think we want to consider systems with > 64 bits of address
> > space so 60-bits is more than enough for PFNs.
> 
> Is it? What about systems with 61..63 bits of address space?

Nevermind, another reply in the thread reminded me that these are PFNs,
so 64-bit PFN == 72 bits of address space.

Although, perhaps it would be better to spec this as nibble and a 60-bit
field rather than by pretending the top of a 64-bit field is special.

(or an octet and a 7 octet field if you prefer)

Ian.


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