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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.01.13 at 17:39, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> 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@xxxxxxx> 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?

> Perhaps we should make this
> hypercall be:
> 
>       uint64_t first_gfn
>       uint64_t first_mfn;
>       uint32_t nr_mfns;
>       uint32_t flags;
>       uint64_t _pad;
> 
> and then it is a nice 32 bytes long?

A trailing 64-bit field seems pretty pointless to me.

Jan


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