Re: [Xen-devel] [v3][PATCH 04/16] xen/passthrough: extend hypercall to support rdm reservation policy

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.06.15 at 10:48, <tiejun.chen@xxxxxxxxx> wrote:
> On 2015/6/18 15:53, Jan Beulich wrote:
>>>>> On 18.06.15 at 09:14, <tiejun.chen@xxxxxxxxx> wrote:
>>> On 2015/6/17 18:11, Jan Beulich wrote:
>>>>>>> On 11.06.15 at 03:15, <tiejun.chen@xxxxxxxxx> wrote:
>>>>> @@ -1577,9 +1578,10 @@ int iommu_do_pci_domctl(
>>>>>            seg = machine_sbdf >> 16;
>>>>>            bus = PCI_BUS(machine_sbdf);
>>>>>            devfn = PCI_DEVFN2(machine_sbdf);
>>>>> +        flag = domctl->u.assign_device.flag;
>>>>>
>>>>>            ret = device_assigned(seg, bus, devfn) ?:
>>>>> -              assign_device(d, seg, bus, devfn);
>>>>> +              assign_device(d, seg, bus, devfn, flag);
>>>>
>>>> I think you should range check the flag passed to make future
>>>> extensions possible (and to avoid ambiguity on what out of
>>>> range values would mean).
>>>
>>> Yeah.
>>>
>>> Maybe I can set this comment,
>>>
>>>       /* Make sure this is always the last. */
>>>
>>> #define XEN_DOMCTL_DEV_NO_RDM           2
>>>
>>>       uint32_t  flag;   /* flag of assigned device */
>>
>> Why would you want to needlessly break the interface is a new
>> constant gets added? It's a domctl, so it can be changed, but we
>> shouldn't change for no reason.
> 
> I just think XEN_DOMCTL_DEV_NO_RDM is prone to represent a sort of 
> ending of all flags, and I also add this comment,
> 
> /* Make sure this is always the last. */
> 
>>
>>> and then
>>>
>>>           flag = domctl->u.assign_device.flag;
>>>           if ( flag > XEN_DOMCTL_DEV_NO_RDM )
>>
>> All that needs updating when a new constant gets added is this
>> line.
> 
> This place really isn't one spotlight to take a attention when a new 
> flag is introduced, right? So what I intend to is trying to make sure we 
> don't need to change this.

Anyone adding a new value will need to test their code. And this
testing would not succeed without the range check above having
got adjusted.

>>>           {
>>>               printk(XENLOG_G_ERR "XEN_DOMCTL_assign_device: "
>>>                      "assign %04x:%02x:%02x.%u to dom%d failed "
>>>                      "with unknown rdm flag %x. (%d)\n",
>>>                      seg, bus, PCI_SLOT(devfn), PCI_FUNC(devfn),
>>>                      d->domain_id, flag, ret);
>>
>> I see absolutely no reason for such a log message.
>>
> 
> Do you mean I should simplify this log message? Or remove completely?

Remove. (And I think you generally need to reduce verbosity of
your additions - please don't mix up what might be useful for your
debugging with what will be useful once the code went in.)

Jan


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