Re: [Xen-devel] [PATCH v2 5/5] xen: replace XEN_GUEST_HANDLE with XEN_GUEST_HANDLE_PARAM when appropriate

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.08.12 at 12:38, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
wrote:
> On Mon, 13 Aug 2012, Jan Beulich wrote:
>> >>> On 13.08.12 at 13:24, Stefano Stabellini 
>> >>> <stefano.stabellini@xxxxxxxxxxxxx> 
> wrote:
>> > On the other hand if you mean casting a XEN_GUEST_HANDLE_PARAM into a
>> > XEN_GUEST_HANDLE to pass it to other internal functions, I don't think
>> > there is any point in that because the other internal functions should
>> > also have XEN_GUEST_HANDLE_PARAMs as parameters.
>> 
>> So you obviously need a cast from "normal" to _PARAM (so that
>> you can pass embedded fields to functions).
> 
> In practice embedded fields are in guest memory, so the first thing Xen
> does is calling copy_from_guest and work with the struct pointer
> directly from that point on.

Perhaps we have a different understanding of embedded fields:
I'm thinking of structure field having XEN_GUEST_HANDLE() type.
An example would be struct mmuext_op's vcpumask field, which
is being passed to vcpumask_to_pcpumask(). This must remain to
be possible (and not just in x86-specific code, where it's mere luck
that both are really identical).

Jan



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