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

On Thu, May 14, 2015 at 10:02:39AM +0800, Chen Fan wrote: > > 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? > > I think that is simple to achieve my original target that implement NIC > passthrough > device migration. because sometimes we assign a native NIC to guest to keep > the > performance of network I/O, due to the MAC limitation of the non-SRIOV NICs, > as > laine said the cost of SRIOV NIC is cheaper than what we try. No, I think you should /not/ attempt to implement this in libvirt at all and instead focus on the higher level apps.