[libvirt] [PATCH v3 01/12] conf: Add definitions for 'uid' and 'fid' PCI address attributes

[Yi Min Zhao]

在 2018/8/22 下午6:09, Andrea Bolognani 写道:
> On Wed, 2018-08-22 at 17:39 +0800, Yi Min Zhao wrote:
>> 在 2018/8/21 下午9:19, Andrea Bolognani 写道:
>>> On Tue, 2018-08-21 at 19:55 +0800, Yi Min Zhao wrote:
>>>>>> For zPCI address, if we use the same strategy as PCI part and user
>>>>>> wants to assign fid=0 to the specific device, he might encounter
>>>>>> assignment failure. At least, according to the doc, 0 shoud be a valid
>>>>>> value to assign to fid.
>>>>> If the user wants to use a specific zPCI address they can simply
>>>>> specify both attributes, eg. uid=1,fid=0 will work just fine with
>>>>> the proposed approach and won't produce errors or cause a new zPCI
>>>>> address to be automatically assigned.
>>>>>
>>>>> If the user only specified fid=0 while leaving uid unspecified,
>>>>> well, an address is going to be picked for them.
>>>> This would be an empty zpci address while parsing XML so that we might
>>>> pick a zpci address with non-zero fid. For example:
>>>>
>>>> dev1: fid=0 (this address would be treated as an unassigned zpci address)
>>>> dev2 (no definition for both fid and uid)
>>>>
>>>> Then the process of assigning addresses will iterate devices as type by
>>>> type.
>>>> If dev2 is processed before dev1, dev2's fid would be assigned by 0.
>>>> This causes
>>>> dev1's fid=1. The result doesn't match what the user wants.
>>> This would be the same as specifying a partial PCI address such as
>>>
>>>     <address type='pci' slot='0x00'/>
>>>
>>> and getting an address with slot != 0x00 back: surprising, perhaps,
>>> but that's the way it's been with PCI addresses forever so you can
>>> assume users are familiar with it by now.
>>>
>>> For zPCI addresses to be inconsistent with this behavior would be
>>> utterly confusing; moreover, if the user really needs the uid and
>>> fid to have certain values, all they have to do is specify both
>>> and libvirt will not attempt to override them.
>> I tried as your idea. It makes everything complicated, especially
>> alloc/reserve/release
>> zpci address. If the user defines uid=1 and fid=0, we don't know whether
>> should
>> reserve fid. (uid=1 fid=0) is the same with (uid=1).
> You should reserve it. The user can either
>
>    * not specify zPCI information at all: automatic assignment will
>      be performed, no error should be reported;
>
>    * specify a *full* zPCI address: manual assignment, will result
>      in either that exact address being used or an error;
>
>    * specify partial information: missing properties will default
>      to zero, which will probably cause errors eg. if only the uid
>      is specified for a bunch of devices.
>
> The last option is less predictable so it should probably never be
> used. All of the above is consistent with how the PCI part works.
>
And then, zpci address instance could be a member of pci address structure?
I mean not using pointer at all?