Re: [PATCH libvirt v1 0/6] Fix ZPCI address auto-generation on s390

On 4/10/20 2:06 PM, Andrea Bolognani wrote: > On Thu, 2020-04-09 at 12:30 +0200, Shalini Chellathurai Saroja wrote: > > The ZPCI address validation or autogeneration does not work as > > expected in the following scenarios > > 1. uid = 0 and fid = 0 > > 2. uid = 0 and fid > 0 > > 3. uid = 0 and fid not specified > > 4. uid not specified and fid > 0 > > 5. 2 ZPCI devices with uid > 0 and fid not specified. > > > > This is because of the following reasons > > 1. If uid = 0 or fid = 0 the code assumes that user has not specified > > the corresponding address > > 2. If either uid or fid is provided, the code assumes that both uid > > and fid addresses are specified by the user. > > I'd have to dig up the old threads, but based on what I remember the > behaviors you describe are entirely intentional. > > For PCI addresses, setting all parts of the address to zero or not > setting it at all is equivalent, and we wanted to be consistent with > that behavior for ZPCI; additionally, zero is not a valid value for > uid so of course neither is the address uid=0 fid=0, which means that > we're not preventing the user from specifying a valid address by > conflating the all-zero address with the unspecified address. > > For partially-specified addresses, the behavior is also the same as > PCI: any part you don't specify is considered to be zero, which > results in > > 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 > fid=x -> uid=0 fid=x -> address is rejected as invalid > uid=x -> uid=x fid=0 -> address is accepted > > So, just like for PCI addresses, you have basically two reasonable > options: either don't specify any zPCI address and leave allocation > entirely up to libvirt, or specify all of the addresses completely: > anything in between will likely not work as you'd expect or want. > > Again, this is based purely on my recollection of design discussions > that happened one and a half years ago, so I might have gotten some > of the details wrong - in which case by all means call me out on > that O:-) > Hi Andrea, sorry for the delayed answer. I (and some others as well) lost some emails on my IMAP account and I just found your answer today.

I can remember that you had a discussion with the original author of the zpci code. There are a few issues with the currently implemented "rules" which partially are not even working as you outlined above in more complex scenarios.