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? 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.