On Wed, May 13, 2020 at 07:41:34PM +0200, Andrea Bolognani wrote: > On Wed, 2020-05-13 at 17:32 +0100, Daniel P. Berrangé wrote: > > On Tue, May 12, 2020 at 12:13:22PM +0200, Boris Fiuczynski wrote: > > > The behavior change would be > > > Current code: > > > uid=0 fid=0 -> uid=0 fid=0 -> address gets autogenerated > > > uid=0 fid=x -> uid=0 fid=x -> address is rejected as invalid > > > uid=0 -> uid=0 fid=0 -> address gets autogenerated > > > > IIUC, in the two cases here where the address gets auto-generated, > > the resulting guest VM successfully boots & runs.... > > > > > With the series applied > > > uid=0 fid=0 -> uid=0 fid=0 -> address is rejected as invalid > > > uid=0 fid=x -> uid=0 fid=x -> address is rejected as invalid > > > uid=0 -> uid=0 fid=0 -> address is rejected as invalid > > > > ...so this proposed change is a functional regression for the > > user. > > > > > The documentation already specifies the uid value range correctly. > > > The fix for users hitting the two scenarios (uid=0 fid=0) and (uid=0) is > > > simple: Remove the zpci definition completely. > > > > This would be taking a users' currently working VM, intentionally > > breaking it, and then making the user pick up the pieces. This is > > an example of a behaviour regression that libvirt promises to not > > do to users. > > The bit of nuance that might be missing here is that existing guests > already have a full zPCI address stored in the domain XML, which > means the wouldn't be affected in any way; additionally, the case > where no zPCI address is provided when defining a new guest, which I > assume is the most common one, will keep working. > > The only scenarios that would no longer work are: > > * the user manually specifies uid=0 fid=0; > * the user manually specifies uid=0 and doesn't specify fid. > > In both cases the user would have gone out of their way to specify > a value for the uid attribute that is documented as being invalid: > > PCI addresses for S390 guests will have a zpci child element, with > two attributes: uid (a hex value between 0x0001 and 0xffff [...] > > https://libvirt.org/formatdomain.html#elementsAddress The effect of specifying zero though is that we perform allocation to assign a non-zero address, which is then valid. The same happens with regular PCI devices if you give slot="0". > As a result, they'd now get a pretty clear error message at define > time instead of confusing behavior across the board. I'm not really > sure anyone would complain about such a change. I don't see this existing behaviour as confusing. It looks like mostly being a docs ommission about auto-allocation taking place. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
