Re: [RFC PATCH 3/16]: PVH xen: Add PHYSDEVOP_map_iomem

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

On Mon, Jan 28, 2013 at 04:47:01PM +0000, Jan Beulich wrote:
> >>> On 28.01.13 at 17:39, Konrad Rzeszutek Wilk <konrad@kernel.org> wrote:
> > On Thu, Jan 24, 2013 at 05:03:50PM -0800, Mukesh Rathor wrote:
> >> On Thu, 24 Jan 2013 15:06:29 +0000
> >> Tim Deegan <tim@xen.org> wrote:
> >> 
> >> > At 17:32 -0800 on 11 Jan (1357925563), Mukesh Rathor wrote:
> >> >DEFINE_XEN_GUEST_HANDLE(physdev_dbgp_op_t);
> >> > >  
> >> > > + 
> >> > > +#define PHYSDEVOP_map_iomem        30
> >> > > +struct physdev_map_iomem {
> >> > > +    /* IN */
> >> > > +    unsigned long first_gfn;
> >> > > +    unsigned long first_mfn;
> >> > > +    unsigned int nr_mfns;
> >> > > +    unsigned int add_mapping;        /* 1 == add mapping;  0 ==
> >> > > unmap */ +
> >> > > +};
> >> > > +typedef struct physdev_map_iomem physdev_map_iomem_t;
> >> > > +DEFINE_XEN_GUEST_HANDLE(physdev_map_iomem_t);
> >> > > +
> >> > 
> >> > This needs documentation.  Also, the arguemnts should be explicitly
> >> > sized to avoid compat difficulties. 
> >> > 
> >> > Tim.
> >> 
> >> Done:
> >> 
> >> /* Map given gfns to mfns where mfns are part of IO space. */
> >> #define PHYSDEVOP_map_iomem        30
> >> struct physdev_map_iomem {
> >>     /* IN */
> >>     uint64_t first_gfn;
> >>     uint64_t first_mfn;
> >>     uint32_t nr_mfns;
> >>     uint32_t add_mapping;        /* 1 == add mapping;  0 == unmap */
> >> 
> >> };
> > 
> > Which is BTW what the Linux tree already has.
> > 
> > Perhaps the 'add_mapping' should be just called 'flags'
> > and have two #defines?
> > 
> > It is also has a bit of an issue when you use __packed__ - that is it
> > will shrink from 32 bytes down to 24 bytes.
> 
> How that? Or really - how would it ever end up being 32 bytes?

It won't. The structure will be aligned on the 8 bytes, so it will
be 24 bytes. Thanks for noticing my mistake.