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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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