Re: [Xen-devel] [PATCH v3 3/3] xen: introduce XENMEM_get_dma_buf and XENMEM_put_dma_buf

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 8 Aug 2013, Jan Beulich wrote:
> >>> On 08.08.13 at 16:44, Stefano Stabellini 
> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > On Thu, 8 Aug 2013, Jan Beulich wrote:
> >> >>> On 08.08.13 at 16:12, Stefano Stabellini 
> >> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> > On Thu, 8 Aug 2013, Jan Beulich wrote:
> >> >> >>> On 05.08.13 at 18:40, Stefano Stabellini 
> >> >> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> >> > @@ -630,8 +690,15 @@ long do_memory_op(unsigned long cmd, 
> >> > XEN_GUEST_HANDLE_PARAM(void) arg)
> >> >> >  
> >> >> >          break;
> >> >> >  
> >> >> > +    case XENMEM_get_dma_buf:
> >> >> > +        /* xen_get_dma_buf_t is identical to xen_memory_exchange_t, 
> >> >> > so
> >> >> > +         * just cast it and reuse memory_exchange */
> >> >> 
> >> >> Then why do you define a new type for it in the first place?
> >> > 
> >> > Because the original hypercall doesn't copy back the mfn if the guest
> >> > it's an autotranslate guest.
> >> > And because it doesn't pin the p2m mappings.
> >> 
> >> Hmm, I'm confused: Here you reason why you want a new type
> >> (note that I said "type", not "sub-hypercall"), ...
> >> 
> >> >> And anyway, the naming of the new sub-op isn't really
> >> >> representing what the operation is capable of.
> >> >> XENMEM_exchange_and_pin would seem to come much closer.
> >> > 
> >> > I like this suggestion. I could also keep xen_memory_exchange as
> >> > argument for XENMEM_exchange_and_pin, as Ian suggested.
> >> 
> >> ... yet here you agree that xen_memory_exchange could be
> >> re-used.
> >  
> > I meant only to keep the same parameter struct xen_memory_exchange.
> 
> And that's what I asked for.

OK, I'll try to be clearer: I think it's reasonable to have a new
hypercall, called XENMEM_exchange_and_pin, using the same struct
parameter of XENMEM_exchange, called struct xen_memory_exchange.
Actually Ian suggested this.

Do you agree?

If not, given that the paramters are actually the same, do you think I
should duplicate and rename the struct as I was doing in this patch?

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