Re: [PATCH v3] xen/public: add comment to struct xen_mem_acquire_resource

[Juergen Gross <jgross@xxxxxxxx>]

On 24.02.22 16:37, Jan Beulich wrote:
> On 24.02.2022 16:24, Juergen Gross wrote:
> > --- a/xen/include/public/memory.h
> > +++ b/xen/include/public/memory.h
> > @@ -662,6 +662,13 @@ struct xen_mem_acquire_resource {
> >        * two calls.
> >        */
> >       uint32_t nr_frames;
> > +    /*
> > +     * Padding field, must be zero on input.
> > +     * In a previous version this was an output field with the lowest
> > +     * bit named XENMEM_rsrc_acq_caller_owned. Future versions of this
> > +     * interface will not reuse this bit with the field being zero on
> > +     * input.
> > +     */
> >       uint32_t pad;
> Did you mean "... being non-zero ..." and "bit" and "field" changing
> positions?
No, why? The current Linux kernel will set pad (the "field") to zero
when doing the hypercall, and it expects the bit to be set or not on
return. This means that the bit is reserved for the case that pad
was zero on input.


Juergen

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