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SubjectRe: [PATCH -v2 2/2] x86: Make Linux guest support optional
On Fri, Jan 25, 2013 at 07:23:35PM +0100, Borislav Petkov wrote:
> On Fri, Jan 25, 2013 at 10:07:31AM -0800, Dmitry Torokhov wrote:
> > > - if (x86_hyper != &x86_hyper_ms_hyperv)
> > > + if (!x86_hyper || strncmp(x86_hyper->name, "VMware", 6))
> > > return -ENODEV;
> >
> > I assume this is a typo as I doubt MS is using the same signature as we
> > do.
>
> Yeah, Vmware is assimilating Microsoft. :-)
>
> Damn copy-paste crap. Sorry, will fix.
>
> > > diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
> > > index cb56e270da11..85f15a6d8798 100644
> > > --- a/drivers/misc/vmw_balloon.c
> > > +++ b/drivers/misc/vmw_balloon.c
> > > @@ -786,7 +786,7 @@ static int __init vmballoon_init(void)
> > > * Check if we are running on VMware's hypervisor and bail out
> > > * if we are not.
> > > */
> > > - if (x86_hyper != &x86_hyper_vmware)
> > > + if (!x86_hyper || strncmp(x86_hyper->name, "VMware", 6))
> > > return -ENODEV;
> > >
> >
> > I wonder why you decided to switch from address matching (which is quite
> > precise and would potentially allow adding signatures without needing
> > to change the drivers) to string matching?
>
> Ok, this is a bit more involved. If we put all hypervisor stuff behind
> CONFIG_HYPERVISOR_GUEST and in the cases where this is disabled,
> the build fails because the x86_hyper_vmware symbol is undefined.
> Alternatively, this doesn't happen when we look at the name.

Can't we make the balloon driver depend on CONFIG_HYPERVISOR_GUEST?

>
> But why would you want to add signatures? Isn't "VMware" enough as a
> name for the vmware hypervisor and why would you need more? And besides,
> hypervisor_x86.name is only a single const char * so you'd need to
> change that struct to add more names...Hm.

We do not _need_ more and have no plans to introduce new ones AFAIK, but
I think that comparing an address of a structure instead of string
comparison is much more elegant and it is safer from typos.

Thanks,
Dmitry


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