Re: [Xen-devel] [PATCH] hvm/altp2m: Clarify the proper way to extend the altp2m interface

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Wei Liu writes ("Re: [PATCH] hvm/altp2m: Clarify the proper way to extend the 
altp2m interface"):
> On Tue, Jul 10, 2018 at 10:33:22AM +0100, George Dunlap wrote:
> > + * Normally hypercalls made by a program in domain 0 in order to
> > + * control a guest would be DOMCTLs rather than HVMOPs.  But in order
> > + * to properly enable the 'internal' use case, as well as to avoid
> > + * fragmentation, all altp2m subops should come under this single
> > + * HVMOP.
> 
> I don't understand this argument. There is no risk of code duplication /
> fragmentation if the implementation is contained within a function.
> Should we choose to split one HVMOP into a DOMCTL and a HVMOP, there is
> now two entries to the internal function, each of which with proper
> checks, but they will call the same internal function eventually.
> 
> I admit I haven't followed the discussion closely.

"each of which with proper checks".  You end up doing some of the
parameter validation twice.  That is very undesirable indeed.

Ian.

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