Re: [libvirt] [RFC v1 4/6] migration: Migration support for ephemeral hostdevs

On 05/13/2015 10:30 PM, Laine Stump wrote: > On 05/13/2015 05:57 AM, Daniel P. Berrange wrote: >> On Wed, May 13, 2015 at 11:36:30AM +0800, Chen Fan wrote: >>> add migration support for ephemeral host devices, introduce >>> two 'detach' and 'restore' functions to unplug/plug host devices >>> during migration. >>> >>> Signed-off-by: Chen Fan <chen.fan.fnst(a)cn.fujitsu.com&gt; >>> --- >>> src/qemu/qemu_migration.c | 171 >>> ++++++++++++++++++++++++++++++++++++++++++++-- >>> src/qemu/qemu_migration.h | 9 +++ >>> src/qemu/qemu_process.c | 11 +++ >>> 3 files changed, 187 insertions(+), 4 deletions(-) >>> >>> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c >>> index 56112f9..d5a698f 100644 >>> --- a/src/qemu/qemu_migration.c >>> +++ b/src/qemu/qemu_migration.c >>> +void >>> +qemuMigrationRestoreEphemeralDevices(virQEMUDriverPtr driver, >>> + virConnectPtr conn, >>> + virDomainObjPtr vm, >>> + bool live) >>> +{ >>> + qemuDomainObjPrivatePtr priv = vm->privateData; >>> + virDomainDeviceDefPtr dev; >>> + int ret = -1; >>> + size_t i; >>> + >>> + VIR_DEBUG("Rum domain restore ephemeral devices"); >>> + >>> + for (i = 0; i < priv->nEphemeralDevices; i++) { >>> + dev = priv->ephemeralDevices[i]; >>> + >>> + switch ((virDomainDeviceType) dev->type) { >>> + case VIR_DOMAIN_DEVICE_NET: >>> + if (live) { >>> + ret = qemuDomainAttachNetDevice(conn, driver, vm, >>> + dev->data.net); >>> + } else { >>> + ret = virDomainNetInsert(vm->def, dev->data.net); >>> + } >>> + >>> + if (!ret) >>> + dev->data.net = NULL; >>> + break; >>> + case VIR_DOMAIN_DEVICE_HOSTDEV: >>> + if (live) { >>> + ret = qemuDomainAttachHostDevice(conn, driver, vm, >>> + dev->data.hostdev); >>> + } else { >>> + ret =virDomainHostdevInsert(vm->def, >>> dev->data.hostdev); >>> + } >> This re-attach step is where we actually have far far far worse >> problems >> than with detach. This is blindly assuming that the guest on the target >> host can use the same hostdev that it was using on the source host. > (kind of pointless to comment on, since pkrempa has changed my opinion > by forcing me to think about the "failure to reattach" condition, but > could be useful info for others) > > For a <hostdev>, yes, but not for <interface type='network'> (which > would point to a libvirt network pool of VFs). > >> This >> is essentially useless in the real world. > Agreed (for plain <hostdev>) > >> Even if the same vendor/model >> device is available on the target host, it is very unlikely to be >> available >> at the same bus/slot/function that it was on the source. It is quite >> likely >> neccessary to allocate a complete different NIC, or if using SRIOV >> allocate >> a different function. It is also not uncommon to have different >> vendor/models, >> so a completely different NIC may be required. > In the case of a network device, a different brand/model of NIC at a > different PCI address using a different guest driver shouldn't be a > problem for the guest, as long as the MAC address is the same (for a > Linux guest anyway; not sure what a Windows guest would do with a NIC > that had the same MAC but used a different driver). This points out the > folly of trying to do migration with attached hostdevs (managed at *any* > level), for anything other than SRIOV VFs (which can have their MAC > address set before attach, unlike non-SRIOV NICs). > > . So should we focus on implementing the feature that support migration with SRIOV VFs at first?