Re: [Xen-devel] [PATCH 2/4] sysctl/libxl: Add interface for returning IO topology data

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/12/14 15:19, Jan Beulich wrote:
>>>> On 08.12.14 at 15:56, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>>> Additionally please add IN and OUT annotations. When I first saw
>>>>> this I assumed they would all be OUT (in which case the long running
>>>>> loop problem mentioned in the reply to one of the other patches
>>>>> wouldn't have been there), matching their CPU counterpart...
>>>> I don't follow this. Are you saying that if ti->max_devs in patch 3/4 is
>>>> an IN (which it is) then we don't have to guard for long-running loops?
>>> If they were all OUT then there wouldn't be a way for the entire
>>> operation to be fooled into going over more devices than there are
>>> in the system.
>> Assuming I add continuations to the loop, too many devices wouldn't be a 
>> problem for the hypervisor, would it? If an unreasonable number is 
>> provided then eventually copy_from_guest() will fault.
> Continuations would address the concern, but it doesn't seem like
> their use is really warranted here.

It depends.  I have one server I have to hand looks like:

[root@mpx1 ~]# lspci | wc -l
1759

(And I believe this one isn't fully populated with devices.)

A continuation is possibly warranted in a case like this, particularly
if an HVM domain is making this hypercall.

~Andrew


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