[libvirt] [PATCH 2/2] qemu: don't update cpu unconditionally for migratable flag

[Jiri Denemark]

On Thu, Sep 21, 2017 at 16:39:39 +0300, Nikolay Shirokovskiy wrote:
> Imagine if we use 'virsh dumpxml --migratable' for offline domain
> to get config to tweak before migration. Currenly cpu section will
> be expanded, host-cpu mode turns into custom and migration fails
> because of ABI check.
> 
> Looks like ABI check does not make much sence for offline migration
> but we don't want host-cpu mode to turn into custom in the first place.
> Using --migratable is reasonable in this case because this flags
> makes changes for inactive configs too like removing automatically
> added parts that old versions can not handle.
> 
> I suggest not to update cpu for inactive configs. This appoach is
> coherent with the way migration works for inactive configs in case
> it is not specified externally to migration: function qemuMigrationCookieXMLFormat
> don't expand cpu too.
> 
> Adding flag for active configs is useless because qemuDomainFormatXML
> will clear it in this case.

Not anymore, see commit v3.7.0-151-g06f75ff2cb.

...
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index d9dff93..3223554 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -6993,9 +6993,6 @@ static char
>      if (qemuDomainUpdateCurrentMemorySize(driver, vm) < 0)
>          goto cleanup;
>  
> -    if ((flags & VIR_DOMAIN_XML_MIGRATABLE))
> -        flags |= VIR_DOMAIN_XML_UPDATE_CPU;
> -
>      ret = qemuDomainFormatXML(driver, vm, flags);
>  
>   cleanup:

This area of code changed recently and it looks like the following now:

    if ((flags & VIR_DOMAIN_XML_MIGRATABLE))
        flags |= QEMU_DOMAIN_FORMAT_LIVE_FLAGS;

    /* The CPU is already updated in the domain's live definition, we need to
     * ignore the VIR_DOMAIN_XML_UPDATE_CPU flag.
     */
    if (virDomainObjIsActive(vm) &&
        !(flags & VIR_DOMAIN_DEF_FORMAT_INACTIVE))
        flags &= ~VIR_DOMAIN_XML_UPDATE_CPU;

But even before the changes, the two lines you are removing were

    if ((flags & VIR_DOMAIN_XML_MIGRATABLE))
        flags |= QEMU_DOMAIN_FORMAT_LIVE_FLAGS;

since commit v0.10.2-133-g28f8dfdccc, i.e., for the last 5 years. I
guess you have some local changes applied to the libvirt tree.

Jirka