Re: [Xen-devel] [PATCH, RFC 1/4] linux: add new (replacement) mmap-batch ioctl

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/01/2010 08:13, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 12.01.10 08:57 >>>
>> Looked okay to me. The only question I saw was regarding
>> xc_get_pfn_type_xxx: I don't think they are used outside libxc, so you can
>> do whatever makes internal sense for libxc (and remove the decls from
>> xenctrl.h).
> 
> The other question (of wider scope) was that on the save format
> currently used: Using bits 28-31 of the PFNs to encode their types
> (effectively wasting bits 32-63 on 64-bit) isn't forward compatible,
> and hence sooner or later will require a change. But of course there
> are other tools limitations (restricting guests to even smaller amounts
> of memory), but those are mostly internal to the tools (i.e. fixing
> them would not break compatibility).

We'll have to stick some kind of version-bump indicator in the save file,
and change the way PFNs and their types are encoded. This is very doable,
when the development window reopens.

This is definitely a 4.1 feature -- it only prevents us saving 1TB+ guests.
It's quite a separate concern from our support for sparse-memory-map hosts.

 -- Keir



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