Re: [Qemu-devel] [PATCH for-2.2] spapr: add host Linux version information to device tree

[Eric Blake <eblake@redhat.com>]

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On 07/17/2014 10:31 PM, cyrilbur@gmail.com wrote:
> It may prove useful know which Linux distribution version the host machine
> is running when an issue in the guest arises but a user cannot access
> the host.
> 
> Signed-off-by: Cyril Bur <cyril.bur@au1.ibm.com>
> ---
>  hw/ppc/spapr.c       |  8 +++++++
>  target-ppc/kvm.c     | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  target-ppc/kvm_ppc.h |  6 +++++
>  3 files changed, 76 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 6b48a26..391d47a 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -375,6 +375,14 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
>      _FDT((fdt_property_string(fdt, "vm,uuid", buf)));
>      g_free(buf);
>  
> +    /*
> +     * Add info to the guest FDT to tell it what linux the host is
> +     */
> +    if (kvmppc_get_linux_host(&buf)) {
> +        _FDT((fdt_property_string(fdt, "linux,host", buf)));
> +        g_free(buf);
> +    }

Ouch.  What does this do for migration?  By exposing it to the guest,
you have made it part of the guest ABI, and now you have limited
yourself to migrate only when the destination host is identical to the
source if you don't want to risk breaking the guest.  Without this, it
seems feasible to migrate from a machine on an older host to another
machine on a newer host.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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