From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v7 2/5] sysctl: Add sysctl interface for
 querying PCI topology
Date: Thu, 23 Apr 2015 18:20:55 -0400
Message-ID: <55397047.2080101@oracle.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: elena.ufimtseva@oracle.com, wei.liu2@citrix.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, andrew.cooper3@citrix.com, dario.faggioli@citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, keir@xen.org, dgdegra@tycho.nsa.gov
List-Id: xen-devel@lists.xenproject.org

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