Re: [Xen-devel] [PATCH v4 1/9] libxc: add DECLARE_HYPERCALL_BUFFER_SHADOW()

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-05-07 at 13:00 +0100, David Vrabel wrote:
> On 07/05/14 12:45, Ian Campbell wrote:
> > On Wed, 2014-04-30 at 19:36 +0100, Andrew Cooper wrote:
> >> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>
> >> DECLARE_HYPERCALL_BUFFER_SHADOW() is like DECLARE_HYPERCALL_BUFFER()
> >> except it is backed by an already allocated hypercall buffer.
> > 
> > I suppose enhancing DECLARE_HYPERCALL_BUFFER_ARGUMENT to have this
> > property has issues with unused variables?
> 
> Yes, I think so. Although I didn't actually try it... Perhaps I should.

Would be good.

> > HYPERCALL_BUFFER_AS_PTR() would have been an alternative implementation
> > (similar to AS_ARG), I suppose there is no particular reason to prefer
> > one over the other?
> 
> Usage of the buffer wouldn't be consistent with a regular
> DECLARE_HYPERCALL_BUFFER().  It would lead to slightly more confusing
> code like:
> 
> DECLARE_HYPERCALL_BUFFER(hbuf);
> unsigned long *to_send = HYPERCALL_BUFFER_AS_PTR(hbuf);
> ...
>     if ( test_bit(p, to_send) )
> ...
>     rc = xc_shadow_control(xch, ctx->domid,
>                       XEN_DOMCTL_SHADOW_OP_CLEAN,
>                       hbuf,
>                       ctx->save.p2m_size
>                       NULL, 0, shadow_stats);
> 
> And it's not as obvious that hbuf and to_send are really the same buffer
> without going back to the declarations.

OK. Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>.

Ian.


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