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Re: [Xen-devel] [PATCH v2] tools/libxl: libxl_get_scheduler should return an int

Julien Grall writes ("Re: [PATCH v2] tools/libxl: libxl_get_scheduler should 
return an int"):
> On 03/21/2014 02:28 PM, Ian Jackson wrote:
> > But then I don't understand why you changed this too.  Either of these
> > changes would suffice by itself, and the former is marginally less
> > fiddly.
> The variable sched is a libxl_scheduler in this function. I can't modify
> the type because it's used with lixbl_scheduler_from_string (see
> xl_cmdimpl.c:6703).

Ah.  I think libxl_scheduler_from_string should be changed too.

Having enums in APIs is not a good idea.  One reason is that on some
architectures the size or passing convention can depend on the range
of the enum.  So backporting a patch that adds a new _value_ to an
enum can result in ABI breakage, even if the new value is never
actually used!

I realise that this is rather counterintuitive and I'm sorry I didn't
spot this when it went in.


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