Re: [PATCH 5/5] xen: Add V4V implementation - padding question

[Ross Philipson <ross.philipson@citrix.com>]

On 06/11/2013 01:40 PM, Ross Philipson wrote:
> On 06/11/2013 01:25 PM, Tim Deegan wrote:
>> At 13:10 -0400 on 11 Jun (1370956242), Ross Philipson wrote:
>>>>
>>>>>> ...
>>>>>> +struct v4v_info
>>>>>> +{
>>>>>> + uint64_t ring_magic;
>>>>>> + uint64_t data_magic;
>>>>>> + evtchn_port_t evtchn;
>>>>>
>>>>> Missing padding at the end?
>>>>>
>>>>
>>>> ack.
>>>>
>>>
>>> At one point during the review of an earlier version of the V4V patch
>>> set, Jan requested that this pad be added to the v4v_info struct. I
>>> understand the padding in all the other structs but I don't understand
>>> this one. This struct is not included in any other structs and is not
>>> followed by any data.
>>
>> 64-bit Xen would see this as a 24-byte struct, even without explicit
>> padding. That would surprise a 32-bit guest that allocated what it saw
>> as a 20-byte struct for Xen to copy into.
>
> Ah yes, of course. Thanks for the quick response.
>
> Ross

I guess that means that this struct is unhappy then...

typedef struct v4vtables_rule
{
     v4v_addr_t src;  -- 8b
     v4v_addr_t dst;  -- 8b
     uint32_t accept; -- 4b
} v4vtables_rule_t;


>
>>
>> Tim.
>
>
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