Re: [Xen-devel] [PATCH: IOEMU & XEN] Change ioreq layout and reduce its size

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 29/10/2009 13:21, "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx> wrote:

>> Reduce size of Xen-qemu shared ioreq structure to 32 bytes. This has
>> two advantages:
> 
> Hi, Keir, 
> Reduce the ioreq structure has these advantages indeed, but do we need to
> consider the following compatibility issues? Thanks!
> 1) HVM guest could migrate/save/restore between the new and old hypervisor if
> vcpu number is less than 32.

It still can, as the ioreq struct is private to the hypervisor and qemu,
neither of which is migrated/saved with the guest.

> 2) Old qemu could work with new hypervisor if guest vcpu number is less than
> 32. 

Qemu, like the toolstack, is expected to be upgraded with the hypervisor.

 -- Keir



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