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Re: [Xen-devel] [PATCH 5 of 5] blkif.h: Define and document the request number/size/segments extension

On 07/02/2012 21:45, "Justin Gibbs" <justing@xxxxxxxxxxxxxxxx> wrote:

>> NAK. No backwards incompatible changes allowed in public headers.
> Sorry for the slow reply on this.  I've been experimenting with ways to keep
> legacy
> source compatibility.  After trying lots of things, testing the impact on an
> existing blkfront
> and blkback implementation, I think the best two options are:
>  1. Version the header file and require consumers to declare the interface
> version
>      they are using.  If the version isn't declared, the default, legacy,
> "version 1.0" will
>      be in effect.
>      Positives:   No change in or constant naming conventions.  Data
> structures and
>                          constants for new features are properly hidden from
> legacy implementations.
>      Negatives: Messy #ifdefs

We already have this. See use of

 -- Keir

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