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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/24/2015 10:09 AM, Boris Ostrovsky wrote:
> On 04/24/2015 03:19 AM, Jan Beulich wrote:
> > > > > On 24.04.15 at 00:20, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > 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.
> > There ought to be a way to create a guest handle from other than
> > the start of an allocated hypercall buffer, but that's really more a
> > question for the tool stack folks.
> Yes, this was question for toolstack people.
(Adjusted TO/CC to reflect this).

> (And my second paragraph was not stated correctly, now that I re-read 
> it. I meant to say that my understanding is that API is expected to 
> make all safety checks on buffers and with 
> set_xen_guest_handle_offset() that I was picturing in my head we could 
> pass in pretty much any pointer. I suppose we could check 'hbuf+offset 
> < sz')
>
> -boris

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel