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

[Peter Krempa]

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. Since this might very well happen the code
will need to be changed to take that option into account. Please note
that that step will make all the things really complicated.

Peter

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