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

[Laine Stump]

On 05/13/2015 04:36 AM, Peter Krempa wrote:
> On Wed, May 13, 2015 at 11:36:30 +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 at cn.fujitsu.com>
>> ---
>>  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
>> @@ -3384,6 +3384,158 @@ qemuMigrationPrepareDef(virQEMUDriverPtr driver,
>>      return def;
>>  }
>>  
>> +int
>> +qemuMigrationDetachEphemeralDevices(virQEMUDriverPtr driver,
>> +                                    virDomainObjPtr vm,
>> +                                    bool live)
>> +{
>> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>> +    virDomainHostdevDefPtr hostdev;
>> +    virDomainNetDefPtr net;
>> +    virDomainDeviceDef dev;
>> +    virDomainDeviceDefPtr dev_copy = NULL;
>> +    virCapsPtr caps = NULL;
>> +    int actualType;
>> +    int ret = -1;
>> +    size_t i;
>> +
>> +    VIR_DEBUG("Rum domain detach ephemeral devices");
>> +
>> +    if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
>> +        return ret;
>> +
>> +    for (i = 0; i < vm->def->nnets;) {
>> +        net = vm->def->nets[i];
>> +
>> +        actualType = virDomainNetGetActualType(net);
>> +        if (actualType != VIR_DOMAIN_NET_TYPE_HOSTDEV) {
>> +            i++;
>> +            continue;
>> +        }
>> +
>> +        hostdev = virDomainNetGetActualHostdev(net);
>> +        if (hostdev->mode != VIR_DOMAIN_HOSTDEV_MODE_SUBSYS ||
>> +            hostdev->source.subsys.type != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_PCI ||
>> +            !hostdev->ephemeral) {
>> +            i++;
>> +            continue;
>> +        }
>> +
>> +        dev.type = VIR_DOMAIN_DEVICE_NET;
>> +        dev.data.net = net;
>> +
>> +        dev_copy = virDomainDeviceDefCopy(&dev, vm->def,
>> +                                          caps, driver->xmlopt);
>> +        if (!dev_copy)
>> +            goto cleanup;
>> +
>> +        if (live) {
>> +            /* nnets reduced */
>> +            if (qemuDomainDetachNetDevice(driver, vm, dev_copy) < 0)
>> +                goto cleanup;
> 
> So this is where the fun begins. qemuDomainDetachNetDevice is not
> designed to be called this way since the detach API where it's used
> normally returns 0 in the following two cases:
> 
> 1) The detach was successfull, the guest removed the device
> 2) The detach request was successful, but guest did not remove the
> device yet
> 
> In the latter case you need to wait for a event to successfully know
> when the device was removed. 

For historical reference: omission of this bit (needing to wait for the
guest to remove the device) was one of the reasons Shradha's patches
couldn't be pushed.