Re: [libvirt] [PATCH] qemu: avoid double reservation of PCI address when hotplugging interface type='hostdev'

On 10/21/19 9:02 AM, Andrea Bolognani wrote: > On Sat, 2019-10-19 at 02:18 -0400, Laine Stump wrote: > > Commit 01ca4010d86 (libvirt v5.1.0) moved address reservation for > > hotplugged interface devices up to an earlier point in > > qemuDomainAttachNetDevice() because some function called when > > hotplugging on aarch64 needed to know the address type, and failed > > when it was "none". > > I don't see anything in the original commit suggesting the change > was connected to aarch64? In fact, for the most part I would expect > aarch64/virt guests to go down the very same code paths as x86/q35 > guests. The secret info is in the emails surrounding the V1 patch that turned into the V2 patch that was eventually pushed: https://www.redhat.com/archives/libvir-list/2018-December/msg00439.html https://www.redhat.com/archives/libvir-list/2018-December/msg00460.html I think the issue is that in the VIR_DOMAIN_NET_TYPE_VHOSTUSER case of the switch statement in qemuDomainAttachNetDevice(), it is calling qemuDomainSupportsNicdev(), and qemuDomainSupportsNicdev has this code: /* non-virtio ARM nics require legacy -net nic */ if (((def->os.arch == VIR_ARCH_ARMV6L) || (def->os.arch == VIR_ARCH_ARMV7L) || (def->os.arch == VIR_ARCH_AARCH64)) && net->info.type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_MMIO && net->info.type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI) return false; return true; So if you were attempting to hotplug a vhostuser device on aarch64 with no address specified in the XML, it would return false, which would cause qemuDomainAttachNetDevice() to fail and log an error.