Re: [Xen-devel] [PATCH v7 2/5] sysctl: Add sysctl interface for querying PCI topology

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/21/2015 03:01 AM, Jan Beulich wrote:
> > +                 ((++dev_cnt > 0x3f) && hypercall_preempt_check()) )
> > +                break;
> > +        }
> > +
> > +        if ( (!ret || (ret == -ENODEV)) &&
> > +             __copy_field_to_guest(u_sysctl, op, u.pcitopoinfo.first_dev) )
> > +            ret = -EFAULT;
> > +    }
> > +    break;
> > +#endif
> With the continuation-less model now used I don't think it makes
> sense to have first_dev and num_devs - for re-invocation all the
> caller needs to do is increment the buffer pointer suitably. I.e.
> you can get away with just a count of devices afaict.
This would require walking xc_hypercall_buffer_t->hbuf. Would something like

    set_xen_guest_handle_raw(sysctl..., (void 
*)HYPERCALL_BUFFER_AS_ARG(foo) + offset)
be acceptable? I don't think I see anything better.

I thought of adding set_xen_guest_handle_offset() that would look 
similar to set_xen_guest_handle() but then I felt that having this in 
API may not be a good idea since xc_hypercall_buffer_t->hbuf would end 
up pointing to memory that is not allocated for full 
xc_hypercall_buffer_t->sz.

-boris

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