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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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