Re: [Xen-devel] [PATCH RESEND 2/2] hvc_xen: implement multiconso

On Wed, 8 Jun 2011, Ian Campbell wrote:
> On Tue, 2011-06-07 at 17:28 +0100, Stefano Stabellini wrote:
> > From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > This patch implements support for multiple consoles:
> > consoles other than the first one are setup using the traditional xenbus
> > and grant-table based mechanism.
> > We use a list to keep track of the allocated consoles, we don't
> > expect too many of them anyway.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> 
> > +static inline int xenbus_devid_to_vtermno(int devid)
> >  {
> > -       if (xencons_if != NULL)
> > -               return xencons_if;
> > -       if (console_pfn == ~0ul)
> > -               return mfn_to_virt(xen_start_info->console.domU.mfn);
> > -       else
> > -               return __va(console_pfn << PAGE_SHIFT);
> > +       return devid + HVC_COOKIE;
> 
> I know this is pre-existing but what is the purpose of offsetting
> vtermno by an arbitrary number?
> 
> Many other callers use 0 or a "unit_address" (which I presume to be
> non-arbitrary). The rtas backend does the same as us, but it just seems
> strange....

Yes, I just kept it the way it was.
We could #define HVC_COOKIE 0 and everything would still work.

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