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

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).