Re: [Xen-devel] [PATCH v4 1/4] x86/HVM: update the start info structure layout

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 17/2/16 a les 10:58, Jan Beulich ha escrit:
>>>> On 16.02.16 at 22:26, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 02/16/2016 12:37 PM, Roger Pau Monne wrote:
>>> diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
>>> index 7b629b1..6ba060f 100644
>>> --- a/xen/include/public/xen.h
>>> +++ b/xen/include/public/xen.h
>>> @@ -787,25 +787,46 @@ typedef struct start_info start_info_t;
>>>   /*
>>>    * Start of day structure passed to PVH guests in %ebx.
>>>    *
>>> - * NOTE: nothing will be loaded at physical address 0, so
>>> - * a 0 value in any of the address fields should be treated
>>> - * as not present.
>>> + * NOTE: nothing will be loaded at physical address 0, so a 0 value in any
>>> + * of the address fields should be treated as not present.
>>> + *
>>> + *  0 +----------------+
>>> + *    | magic          | Contains the magic value HVM_START_MAGIC_VALUE
>>> + *    |                | ("xEn3" with the 0x80 bit of the "E" set).
>>> + *  4 +----------------+
>>> + *    | version        | Version of this structure. Current version is 0. 
>>> New
>>> + *    |                | versions are guaranteed to be 
>>> backwards-compatible.
>>
>> #define XEN_HVM_START_INFO_VERSION   0
> 
> What would that buy us? Once it gets bumped to 1, consumers
> would need to check against literal zero anyway.

I agree with Jan that this doesn't seem very useful, the headers don't
have to be in sync with the underlying hypervisor, so it's better to
just use literals instead of defines.

Roger.

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