Re: [RFC PATCH 2/5] conf: Add an iommufd member struct to virDomainIOMMUDef

On 5/20/2025 6:01 AM, Daniel P. Berrangé wrote: > > Add support for an "iommufd" virDomainIOMMUDef member that will be > > translated to a qemu "-object iommufd" command line argument. This > > iommufd struct has an "id" member to specify the iommufd object id > > that can be associated with a passthrough device, and an "fd" > > member to specify the fd for externally opening the /dev/iommu and > > VFIO cdev by a management layer. > > > > @@ -28310,6 +28406,16 @@ virDomainIOMMUDefFormat(virBuffer *buf, > > virXMLFormatElement(&childBuf, "driver", &driverAttrBuf, NULL); > > + if (iommu->iommufd) { > > + virBufferAddLit(&childBuf, "<iommufd>\n"); > > + virBufferAdjustIndent(&childBuf, 2); > > + virBufferAsprintf(&childBuf, "<id>%s</id>\n", iommu->iommufd->id); > > + if (iommu->iommufd->fd) > > + virBufferAsprintf(&childBuf, "<fd>%s</fd>\n", iommu->iommufd->fd); > I'm not convinced we should be exposing the QEMU "id" in the XML. > It is an identifier libvirt uses internally for configuring > QEMU, but I don't see a reason why the end user needs to control > its name. I'm similarly not sure we should expose an FD to > users eitherm, just use that internally when talking to QEMU. > > IOW, why aren't we just having "iommu='yes'" as an attribute > on the <iommu> device, avoiding all the logic below that > tries to force all devices to use the same configuration. That makes sense - I will simply have an attribute like "iommufd='yes'" as an attribute in the next revision instead of having users specify the iommufd id themselves. As for exposing an FD to users, this is meant to mirror the qemu implementation where users can specify the FD string [0], so I think we should keep this part as-is.