Re: [Xen-devel] [PATCH for-4.5 v6 05/16] tools: Add vmware_port support

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 09/24/2014 05:31 PM, Don Slutz wrote:
> On 09/23/14 08:20, Ian Campbell wrote:
> > On Mon, 2014-09-22 at 12:42 -0400, Don Slutz wrote:
> > > > The latter would allow moving to buildinfo.u.hvm, which would be nicer
> > > > from the libxl PoV, I think.
> > > I could not find "buildinfo.u.hvm":
> > >
> > >
> > > dcs-xen-54:~/xen>git grep buildinfo.u.hvm
> > > dcs-xen-54:~/xen>
> > >
> > >
> > > So unable to comment.
> > It's in the idl, next to createinfo.
> I take that to mean:
>
>
> libxl_domain_config = Struct("domain_config", [
>     ("c_info", libxl_domain_create_info),
>     ("b_info", libxl_domain_build_info),
> ...
>
> I.E.
>
> b_info->u.hvm
>
>
> > > > If yes then I still think you would want to set the default based on
> > > > vmware-hw, wouldn't you?
> > > I guess so since this is a BOOLEAN.
> > defbool I hope.
> Yes.
>
> > >    Currently I do not know of a way to
> > > say "set vmware_hw to 7
> > > if vmware_port is true and vmware_hw is not specified".
> > That's an error case, isn't it? Or at least a vmware_port is ignored
> > case.
> Nope.  But I will agree that I have not done a lot with 3 (at least)
> state booleans.  The 3 states being true, false, and not specified.
>
> And vmware_port is not ignored.
>
> > What I suggested was "if vmware_hw is non-zero then set vmware_port".
> I am reading that as "set vmware_port if not specified".  To avoid
> complexity, I am treating vmware_hw as a boolean.  Using this
> I get the following table:
>
> _hw   _port
>  0     0        Just like today
>  1     0        Only cpuid leaves change -- very unlikey
>  1     1        Full VMware mode
>  0     1        VMware hyper call mode.
>
> Adding U for unspecified:
>
> _hw   _port
>  U     U        ==> _hw=0 _port=0
>  0     U        ==> _hw=0 _port=0
>  1     U        The case in question.
>  U     0        ==> _hw=0 _port=0
>  U     1        What I was talking about.
>  0     0        Just like today
>  1     0        Only cpuid leaves change -- very unlikey
>  1     1        Full VMware mode
>  0     1        VMware hyper call mode.
>
> The problem here is that vmware_hw is not a boolean and there is
> currently not a value that lets you know it has not been specified.
>
> So I think it is just more confusing to have vmware_hw change
> the default of vmware_port but the inverse is not true.
So is it the case that if you specify vmware_hw with a value that your 
guest isn't expecting, it may not work?
I think the main thing Ian wants is probably a simple way for people to 
just turn everything on.  Having vmware_hw!=0 => vmware_port defaults to 
1 seems like a reasonable way to do that.
We could almost think of vmware_port as an "advanced" option that most 
people don't need to set: i.e., you only need to set it if you want one 
of the "unusual" modes (like CPUID-only or hypercall-only).
 -George

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