Re: [Xen-devel] [PATCH 3/4] xen kconfig: add dom0 support help text

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 6 Jan 2012, Andrew Jones wrote:
> ----- Original Message -----
> > On Fri, 6 Jan 2012, Andrew Jones wrote:
> > > > Almost all of the things which dom0 needs (e.g. PCI device
> > > > management
> > > > etc) is also required by a domU with passthrough enabled so the
> > > > savings
> > > > are really very slight.
> > > > 
> > > > We are talking less than 1k of code AFAICT, 319 bytes for
> > > > arch/x86/xen/vga.o and 573 for drivers/xen/xenfs/xenstored.o plus
> > > > whatever xen_register_gsi (a couple of dozen lines of code) adds
> > > > to
> > > > arch/x86/pci/xen.o. grep doesn't show CONFIG_XEN_DOM0 being used
> > > > anywhere else. What savings do you see in practice from disabling
> > > > just
> > > > this symbol?
> > > 
> > > I completely agree that the saving are near none. The savings,
> > > however,
> > > aren't the only reason to drive the change. It's actually the
> > > symbol
> > > name itself. Unfortunately configs can be perceived as a contract
> > > of
> > > support, i.e. if feature xyz is enabled in the distro's config,
> > > then
> > > the distributor must have selected, and therefore will support,
> > > said
> > > feature.
> > > 
> > > I didn't make this motivation clear in my initial post, because I
> > > was
> > > hoping to spare people some eye rolling.
> > 
> > I thought that in the kernel community we make decisions based on
> > technical merits rather than "contracts of support".
> 
> Sorry.
> 
> > Given that disabling the symbol saves near to nothing, the logical
> > thing
> > to do is removing the symbol altogether.
> > 
> 
> I thought of that too. If the symbol just goes away, then my
> non-technical requirement will be met and the functionality will
> stay. I consider that a bigger win actually. I didn't suggest it
> though, since I've never done any dom0 development, nor had any
> consideration for dom0 code needs of the future. With
> anti-credentials like that, I'd guess it'd be tougher for me to sell
> the need to remove it, than it is for me to just make it
> configurable.
 
The reason to remove is easy: it is already a silent option and
disabling it saves almost nothing.
I think that removing it should be easy enough but if you don't
feel confident doing it, I can come up with a patch.

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