Re: [PATCH v3 07/14] qemu: Wire up <memory/> live update

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On Fri, Apr 23, 2021 at 15:24:29 +0200, Michal Privoznik wrote:
> As advertised in one of previous commits, we want to be able to
> change 'requested-size' attribute of virtio-mem on the fly. This
> commit does exactly that. Changing anything else is checked for
> and forbidden.
> 
> Once guest has changed the allocation, QEMU emits an event which
> we will use to track the allocation. In the next commit.
> 
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
>  src/conf/domain_conf.c       |  36 ++++++++
>  src/conf/domain_conf.h       |   4 +
>  src/libvirt_private.syms     |   1 +
>  src/qemu/qemu_driver.c       | 172 ++++++++++++++++++++++++++++++++++-
>  src/qemu/qemu_hotplug.c      |  18 ++++
>  src/qemu/qemu_hotplug.h      |   5 +
>  src/qemu/qemu_monitor.c      |  13 +++
>  src/qemu/qemu_monitor.h      |   5 +
>  src/qemu/qemu_monitor_json.c |  15 +++
>  src/qemu/qemu_monitor_json.h |   5 +
>  10 files changed, 273 insertions(+), 1 deletion(-)

[...]

> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index d908e95ba7..9a241ad551 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -7130,6 +7130,165 @@ qemuDomainChangeDiskLive(virDomainObj *vm,
>      return 0;
>  }
>  
> +
> +static bool
> +qemuDomainChangeMemoryLiveValidateChange(const virDomainMemoryDef *oldDef,
> +                                         const virDomainMemoryDef *newDef)
> +{

I must say this function feels almost as the ABI stability checker.

> +    /* The only thing that is allowed to change is 'requestedsize' for virtio
> +     * model. */

Also this is a bit weird. You mention that we are dealing with
virtio-mem ...

> +    if (oldDef->model != newDef->model) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory model from '%s' to '%s'"),
> +                       virDomainMemoryModelTypeToString(oldDef->model),
> +                       virDomainMemoryModelTypeToString(newDef->model));
> +        return false;
> +    }
> +
> +    if (oldDef->access != newDef->access) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory access from '%s' to '%s'"),
> +                       virDomainMemoryAccessTypeToString(oldDef->access),
> +                       virDomainMemoryAccessTypeToString(newDef->access));
> +        return false;
> +    }
> +
> +    if (oldDef->discard != newDef->discard) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory discard from '%s' to '%s'"),
> +                       virTristateBoolTypeToString(oldDef->discard),
> +                       virTristateBoolTypeToString(newDef->discard));
> +        return false;
> +    }
> +
> +    if (!virBitmapEqual(oldDef->sourceNodes,
> +                        newDef->sourceNodes)) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                       _("cannot modify memory source nodes"));
> +        return false;
> +    }
> +
> +    if (oldDef->pagesize != newDef->pagesize) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory pagesize from '%llu' to '%llu'"),
> +                       oldDef->pagesize,
> +                       newDef->pagesize);
> +        return false;
> +    }
> +
> +    if (STRNEQ_NULLABLE(oldDef->nvdimmPath, newDef->nvdimmPath)) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory path from '%s' to '%s'"),
> +                       NULLSTR(oldDef->nvdimmPath),
> +                       NULLSTR(newDef->nvdimmPath));
> +        return false;
> +    }

... but also check stuff not relevant to virtio-mem ...

> +
> +    if (oldDef->alignsize != newDef->alignsize) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory align size from '%llu' to '%llu'"),
> +                       oldDef->alignsize, newDef->alignsize);
> +        return false;
> +    }
> +
> +    if (oldDef->nvdimmPmem != newDef->nvdimmPmem) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory pmem from '%d' to '%d'"),
> +                       oldDef->nvdimmPmem, newDef->nvdimmPmem);
> +        return false;
> +    }
> +
> +    if (oldDef->targetNode != newDef->targetNode) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory targetNode from '%d' to '%d'"),
> +                       oldDef->targetNode, newDef->targetNode);
> +        return false;
> +    }
> +
> +    if (oldDef->size != newDef->size) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory size from '%llu' to '%llu'"),
> +                       oldDef->size, newDef->size);
> +        return false;
> +    }
> +
> +    if (oldDef->labelsize != newDef->labelsize) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory label size from '%llu' to '%llu'"),
> +                       oldDef->labelsize, newDef->labelsize);
> +        return false;
> +    }
> +    if (oldDef->blocksize != newDef->blocksize) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory block size from '%llu' to '%llu'"),
> +                       oldDef->blocksize, newDef->blocksize);
> +        return false;
> +    }
> +
> +    /* requestedsize can change */
> +
> +    if (oldDef->readonly != newDef->readonly) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                       _("cannot modify memory pmem flag"));
> +        return false;
> +    }
> +
> +    if ((oldDef->uuid || newDef->uuid) &&
> +        !(oldDef->uuid && newDef->uuid &&
> +          memcmp(oldDef->uuid, newDef->uuid, VIR_UUID_BUFLEN) == 0)) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                       _("cannot modify memory UUID"));
> +        return false;
> +    }
> +
> +    switch (oldDef->model) {
> +    case VIR_DOMAIN_MEMORY_MODEL_VIRTIO_MEM:
> +        break;
> +
> +    case VIR_DOMAIN_MEMORY_MODEL_NONE:
> +    case VIR_DOMAIN_MEMORY_MODEL_DIMM:
> +    case VIR_DOMAIN_MEMORY_MODEL_NVDIMM:
> +    case VIR_DOMAIN_MEMORY_MODEL_VIRTIO_PMEM:
> +    case VIR_DOMAIN_MEMORY_MODEL_LAST:
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("cannot modify memory of model '%s'"),
> +                       virDomainMemoryModelTypeToString(oldDef->model));
> +        return false;

... but at the end only allow virtio-mem, so the irrelevant checks are
actually not even necessary.

> +        break;
> +    }
> +
> +    return true;
> +}
> +
> +
> +static int
> +qemuDomainChangeMemoryLive(virQEMUDriver *driver G_GNUC_UNUSED,
> +                           virDomainObj *vm,
> +                           virDomainDeviceDef *dev)
> +{
> +    virDomainMemoryDef *newDef = dev->data.memory;
> +    virDomainMemoryDef *oldDef = NULL;
> +
> +    oldDef = virDomainMemoryFindByDeviceInfo(vm->def, &dev->data.memory->info);
> +    if (!oldDef) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("memory '%s' not found"), dev->data.memory->info.alias);

[1]

> +        return -1;
> +    }
> +
> +    if (!qemuDomainChangeMemoryLiveValidateChange(oldDef, newDef))
> +        return -1;
> +
> +    if (qemuDomainChangeMemoryRequestedSize(driver, vm,
> +                                            newDef->info.alias,
> +                                            newDef->requestedsize) < 0)
> +        return -1;
> +
> +    oldDef->requestedsize = newDef->requestedsize;
> +    return 0;
> +}
> +
> +
>  static int
>  qemuDomainUpdateDeviceLive(virDomainObj *vm,
>                             virDomainDeviceDef *dev,
> @@ -7171,6 +7330,18 @@ qemuDomainUpdateDeviceLive(virDomainObj *vm,
>          ret = qemuDomainChangeNet(driver, vm, dev);
>          break;
>  
> +    case VIR_DOMAIN_DEVICE_MEMORY:
> +        oldDev.data.memory = virDomainMemoryFindByDeviceInfo(vm->def, &dev->data.memory->info);
> +        if (oldDev.data.memory) {

Also this is a bit weird too. Here you do this optionally if
virDomainMemoryFindByDeviceInfo finds the device ...

> +            if (virDomainDefCompatibleDevice(vm->def, dev, &oldDev,
> +                                             VIR_DOMAIN_DEVICE_ACTION_UPDATE,
> +                                             true) < 0)
> +                return -1;
> +        }
> +
> +        ret = qemuDomainChangeMemoryLive(driver, vm, dev);

... but here the first thing that is done is that virDomainMemoryFindByDeviceInfo
is called again and a NULL return is fatal.

> +        break;
> +
>      case VIR_DOMAIN_DEVICE_FS:
>      case VIR_DOMAIN_DEVICE_INPUT:
>      case VIR_DOMAIN_DEVICE_SOUND:

With the wierdness reduced:

Reviewed-by: Peter Krempa <pkrempa@xxxxxxxxxx>




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