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

[Yi Min Zhao]

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:
>> 在 2018/8/21 下午7:00, Andrea Bolognani 写道:
>>> On Tue, 2018-08-21 at 17:35 +0800, Yi Min Zhao wrote:
>>>> I want to ask a question. For pci address, any pci device can't use slot 0.
>>>> Is that a reason why PCI part could treat all zeros as empty address?
>>> A PCI address where all attributes are zero can't be used, so
>>> there's no ambiguity there; same for a zPCI address where all
>>> attributes are zero, which also can't be used.
>> Yes, uid must be non-zero value. But the user could only define fid like
>> you mentioned below. Validation check happens during parsing xml.
>> So if the user only defines fid=0, zpci address (fid=0, uid=0 although the
>> user doesn't specify uid value) is going to be invalid as PCI address
>> check logic.
> In the context of PCI addresses, empty implies invalid but during
> XML parsing the address is only validated if it's not empty. If
> that was not the case, an empty address would never have a chance
> to be automatically filled in by libvirt :)
>
>> UID and FID must be unique separately, but we can't treat
>> them as a combination. This doesn't like PCI
>> address(domain:bus:slot:function).
> I asked a question about this in reply to patch 09/12 yesterday
> by the way, and it would be great if you could answer it.
I answered you in the morning.
>
>>>> 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).