Re: [libvirt] [PATCH v2 1/3] storage: Fix existing parent check for vHBA creation

On 07/19/2017 10:21 AM, Erik Skultety wrote: > On Wed, Jul 19, 2017 at 09:59:06AM -0400, John Ferlan wrote: >> >> >> On 07/19/2017 07:38 AM, Erik Skultety wrote: >>> On Tue, Jul 18, 2017 at 11:10:38AM -0400, John Ferlan wrote: >>>> https://bugzilla.redhat.com/show_bug.cgi?id=1472277 >>>> >>>> Commit id '106930aaa' altered the order of checking for an existing >>>> vHBA (e.g something created via nodedev-create functionality outside >>>> of the storage pool logic) which inadvertantly broke the code to >>>> decide whether to alter/force the fchost->managed field to be 'yes' >>>> because the storage pool will be managing the created vHBA in order >>>> to ensure when the storage pool is destroyed that the vHBA is also >>>> destroyed. >>> >>> Right, I agree with this - unless the user explicitly states they want the >>> pre-created vHBA to be managed, we don't force any setting. I was wondering >>> though, what about a use case when the user wants the vHBA to be auto-created, >>> but non-managed at the same time...(yeah, I know I'm stretching it a bit with >>> these unlikely scenarios, but then, you'd surely agree, you've already seen >>> some of similar sort and one can never expect what creative ways of defining >>> the XML are there to be found :)) >> >> I think you're becoming the new vHBA expert ;-) >> >> In this case, I tell them to go see figure one or go read the docs. From >> the storage pool page, managed description: "For configurations that do >> not provide an already created vHBA from a 'virsh nodedev-create', >> libvirt will set this property to "yes"." >> >>> >>> I was also about to point out in the previous version, that I didn't like how >>> complex virNodeDeviceCreateVport was getting - do wwnn and wwpn relate to a >>> vHBA at all or is it a regular HBA, does the vHBA exist already or should we >>> actually create and manage it. >>> >> >> The wwnn/wwpn are the wwnn/wwpn used to create the vHBA. Typically, a >> SAN admin will "assign" the pair (there's some specific rules about >> them). If not provided for a storage pool, then it's an XML error. For a >> nodedev it's possible to have libvirt generate a wwnn/wwpn, which yes, >> is quite confusing. In doing so libvirt uses a specific base and adds to >> it (see virRandomGenerateWWN and cover at least one eye). >> >> I agree in general about the "complexity" thing, but as time has gone on >> requests for new ways to determine which parent to use has caused code >> bloat. Complexity is a time factored calculation. When originally >> implemented using "host#" for parent was perfectly fine, but then >> someone realized that it should be "scsi_host#". Then someone said, that >> "scsi_host#" wasn't good enough because it can change between reboots. >> So parent by wwnn/wwpn was added. During the discussions for that >> someone else said what about using the fabric_wwn in order to find a >> parent. Oh and the "future" holds being able to define multiple vHBA's >> because it's felt migration of domains using vHBA pools is going to need >> more than one vHBA because on the target host using the same wwnn/wwpn >> won't work (although I have doubts here, but haven't had the cycles to >> investigate). >> >> If you're interested, go read the tail end of the wiki >> (http://wiki.libvirt.org/page/NPIV_in_libvirt) - it'll show a bit of the >> history of how things looked at one time. >> >> TBH: Sometimes I think QE reads the code and figures out a way to create >> bugs based on assumptions the code makes rather than making sure the >> intended use cases "work properly". Hence this whole need to know >> whether the parent is the HBA or the vHBA. Why would *anyone* provide >> the HBA parent wwnn/wwpn when it's perfectly fine to create a storage >> pool of the HBA without it via: >> >> <adapter type='scsi_host' name='scsi_host3'/> >> >> but no, someone wants to be inventive and think/believe: >> >> <adapter type='fc_host' [parent='scsi_host3'] wwnn='HBA_wwnn' >> wwpn='HBA_wwpn'/> >> >> should work as well (where HBA_wwnn/wwpn are the wwnn/wwpn of scsi_host3 >> in this example). >> >> The second XML isn't illegal, but because scsi_host3 has vHBA > > Well, I'd call it a misconfiguration, how can a device be a parent to itself? > That's not what the attribute's supposed to serve and using it this way is a > misuse - we should either ignore it in that case or return error. The storage > pool won't start but it should never have in the first place and the XML def > won't disappear in this case, so IMHO we could and probably should forbid it. > Because it hasn't really been characterized as a misconfiguration previously. I doubt anyone outside of QE has ever done something like this as there's no reason to do so. If they want to use the HBA they'd use the 'scsi_host' format. IMO: something with 'fc_host' what uses the HBA wwnn/wwpn is misconfigured because it's not a vHBA then, but there's been no attempt to prohibit that configuration, hence the current mess. I'd be perfectly fine with turning this particular bz/check into - don't configure things this way because it's not how it's supposed to work. If you want a storage pool backed to an HBA, then use the scsi_host syntax. If you want a vHBA/NPIV then use the fc_host syntax.