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

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.