[Xen-devel] Re: vtsc in domain builder

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 16/09/2009 00:32, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> Was this change due to some backward compatibility reason?
> 
> I found the compatibility issue describe here:
> 
> http://xen.markmail.org/message/usjxnjyp3csm3uct?q=superpages+date:200907
> 
> So it seems even more important that I somehow claim
> a field (or at least a bit) in struct xc_dom_image.
> Any help to get this right would be appreciated
> as getting it wrong clearly has some non-obvious
> consequences.

Well, the main issue was the original patch broke API compatibility. Fixing
ABI compatibility in the fixup patch was just gravy.

I suggest you split the superpages int8_t into a bitfield, e.g:
uint8_t superpages:1, vtsc:1;
Putting superpages first should maintain compatibility as far as possible.
The bitfield has to be switched to be unsigned - we got bit by that before.

 -- Keir



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