Re: [Xen-devel] [PATCH 1 of 2] After preparing a page for page-in, allow immediate fill-in of the page contents

["Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>]

> Andres Lagar-Cavilla writes ("[PATCH 1 of 2] After preparing a page for
> page-in, allow immediate fill-in of the page contents"):
>> -    /* OP_ENABLE */
>> -    uint64_aligned_t shared_addr;  /* IN:  Virtual address of shared
>> page */
>> +    union {
>> +        /* OP_ENABLE IN:  Virtual address of shared page */
>> +        uint64_aligned_t shared_addr;
>> +        /* PAGING_PREP IN: buffer to immediately fill page in */
>> +        uint64_aligned_t buffer;
>> +    } u;
>
> Do we care that this interface is very binary-incompatible ?  Is there
> a flag or version somewhere where we can at least arrange for this to
> be detected ?  Perhaps we should allocate a new domctl number for this
> version, so old code gets "no idea what you're talking about" rather
> than wrong behaviour ?

I turned the field into a union of the same size, so it should be binary
compatible. Should...

There is no reason to use a union other than clarity: "this field is used
for different purposes in different domctls".

I think this is fine, but your call.

Andres
>
> Ian.
>



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