Re: [PATCH v5 1/3] x86/viridian: Re-purpose the HVM parameter to be a feature mask

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2014-08-13 at 12:09 +0100, Paul Durrant wrote:
> > -----Original Message-----
> > From: Ian Jackson [mailto:Ian.Jackson@eu.citrix.com]
> > Sent: 12 August 2014 16:26
> > To: Paul Durrant
> > Cc: xen-devel@lists.xen.org; Keir (Xen.org); Jan Beulich; Ian Campbell;
> > Stefano Stabellini
> > Subject: Re: [PATCH v5 1/3] x86/viridian: Re-purpose the HVM parameter to
> > be a feature mask
> > 
> > Paul Durrant writes ("[PATCH v5 1/3] x86/viridian: Re-purpose the HVM
> > parameter to be a feature mask"):
> > > The viridian option in xl.cfg(5) has also been changed to a string list so
> > > that the sets can be individually sepcified. For compatibility, if the
> > > option is specified as a boolean, then a true (1) value will be translated
> > > to a string list containing "base" and "freq".
> > 
> > This is correct, I think.  But the libxl API should be in numbers, not
> > a string list.  Text to string conversion should be done in xl, not
> > libxl.
> > 
> > I think that these flag values ought to be represented in the IDL, so
> > that text-to-string conversion can be done automatically.
> > 
> > I looked at the existing IDL definitions and there don't seem to be
> > any flags of this kind.  So I think this will involve a inventing new
> > kind of IDL type.  It might be possible to adapt Enumeration.  It
> > might be enough simply to provide a way to make an Enumeration whose
> > corresponding typedef is to a uint32_t.
> > 
> > Does this make any kind of sense ?
> > 
> 
> Yes, it does. I guess what we really want is an 'enumeration list'
> then - i.e. strings get translated via enumeration and then
> concatenated into a list.  Is there any precedent for such a thing?

For singleton enums there is, but not for lists of such things. I don't
think.

But isn't what you actually want here a struct viridian-ish thing
containing a bunch of (def)bools, one per fearture? That would seem like
a more natural interface for a libxl app (a list of VIRIDIAN_FEATURE_X,
VIRIDIAN_FEATURE_Y doesn't seem quite right to me).

Ian.