Re: [libvirt] [PATCH 16/18] qemu: Support scsi controller model=virtio-{non-}transitional

On Tue, 2019-01-22 at 16:27 -0500, Cole Robinson wrote: > On 01/22/2019 12:39 PM, Cole Robinson wrote: >> On 01/21/2019 11:49 AM, Andrea Bolognani wrote: >>> Completely agree with the rationale here; however, in order to >>> really match the way other devices are handled, I think we should >>> make it so you can use >>> >>> <controller type='scsi' model='virtio'/> >>> >>> as well, which of course would behave the same as the currently >>> available version. What do you think? >> >> Yes I agree it would be nice to add that option. I suggest we make it a >> separate issue from this series though incase it's a contentious idea, >> v2 is already shaping up to be ~30 patches... I don't think that's going to be particularly controversial, and we should really make sure we get all the user-facing bits in at the same time IMHO, so I'd say go for it... If you're really unsure about it you can add that model in a separate patch right after this one, that way if someone happens not to like that we can drop it and otherwise we can squash them together before pushing.

>>> Using strstr() here is kinda crude, especially since the caller has >>> enough information to pass the appropriate virDomainControllerType >>> value, both in this case and later on for serial controllers. >>> >>> I'd say just add yet another argument to the function. Yeah, it >>> starts to get quite unsightly, but I'd really rather not resort to >>> string comparison when a nice, type safe enum will do. >> >> Yeah it's hacky. Adding another arg here is going to add extra pain if >> when this is merged into qemuBuildVirtioStr, most callers are going have >> NULL arguments, and an increased chance of new future callers passing in >> incorrect values and accidentally triggering a wrong code path. I feel >> like this is another argument for the separated BuildTransitional or >> whatever, but I'm not sold either way so I'll stick with your suggestion > > What do you think of this approach? See the attached two patches. It > adds a domain_conf.c function virDomainDeviceSetData which makes it > easier to create a virDomainDeviceDef. qemuBuildVirtioDevStr callers now > pass in a virDomainDeviceType and the specific DefPtr for their device > (virDomainDiskDefPtr, virDomainNetDefPtr etc). qemuBuildVirtioDevStr > then turns that into a virDomainDeviceDef and acts on that locally. > > Saves having to extend the argument list several times (like this > example above, and the net->model string example). Seperately I think > virDomainDeviceSetData can be used to clean up some device interactions > elsewhere too I like it! I actually wanted to suggest something like that earlier, but for some reason I thought it would be more complicated than it turned out to be... Better yet, you don't even need to add that switch statement to qemuBuildVirtioDevStr(): you can just use virDomainDeviceGetInfo() instead, thus making the code shorter and nicer :)