Re: [Xen-devel] [PATCH v2 13/21] xen/dts: Add hypercalls to retrieve device node information

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.08.14 at 17:17, <julien.grall@xxxxxxxxxx> wrote:
> On 08/01/2014 09:50 AM, Jan Beulich wrote:
>>>>> On 31.07.14 at 17:00, <julien.grall@xxxxxxxxxx> wrote:
>>> --- a/xen/include/public/domctl.h
>>> +++ b/xen/include/public/domctl.h
>>> @@ -946,6 +946,44 @@ typedef struct xen_domctl_vcpu_msrs 
>>> xen_domctl_vcpu_msrs_t;
>>>  DEFINE_XEN_GUEST_HANDLE(xen_domctl_vcpu_msrs_t);
>>>  #endif
>>>  
>>> +/* Device Tree: Retrieve informations about a device node */
>>> +struct xen_domctl_dtdev_op {
>>> +    /* IN */
>>> +    uint32_t plen;                  /* Length of the path */
>>> +    XEN_GUEST_HANDLE(char) path;    /* Path to the device tree node */
>> 
>> XEN_GUEST_HANDLE_64?
> 
> Right. I never know when I should use XEN_GUEST_HANDLE_64 or
> XEN_GUEST_HANDLE.

The former is for interfaces without compat mode translation, i.e.
mainly domctl and sysctl (other toolstack only ones may use them
too).

> FYI, it's exactly the same on ARM.
> 
>> And padding between the two above
>> members, or fields re-ordered?
> 
> I can reorder the field.
> [...]
>>> +        } irq;
>>> +        struct {
>>> +            xen_pfn_t mfn;
>>> +            xen_pfn_t nr_mfn;
>>> +        } mmio;
>>> +        struct {
>>> +            uint32_t len;           /* IN: Size of buffer. OUT: Size 
>>> copied 
> */
>>> +            XEN_GUEST_HANDLE_64(char) compat;
>> 
>> Padding again?
> 
> I will invert the 2 fields.

The re-ordering won't help unless there's another field following which
fills the then trailing padding space.

Jan


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