Re: [Qemu-devel] [PATCHv4] migration: catch unknown flags in ram_load

[Eric Blake <eblake@redhat.com>]

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On 06/10/2014 03:29 AM, Peter Lieven wrote:
> if a saved vm has unknown flags in the memory data qemu
> currently simply ignores this flag and continues which
> yields in an unpredictable result.
> 
> This patch catches all unknown flags and aborts the
> loading of the vm. Additionally error reports are thrown
> if the migration aborts abnormally.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---

> +    while (!ret) {
>          addr = qemu_get_be64(f);
>  
>          flags = addr & ~TARGET_PAGE_MASK;

> -
> -        if (flags & RAM_SAVE_FLAG_COMPRESS) {
> +        } else if (flags & RAM_SAVE_FLAG_COMPRESS) {
>              void *host;

>          } else if (flags & RAM_SAVE_FLAG_XBZRLE) {

>          } else if (flags & RAM_SAVE_FLAG_HOOK) {
>              ram_control_load_hook(f, flags);
> +        } else if (flags & RAM_SAVE_FLAG_EOS) {

Umm, is the migration format specifically documented as having at most
one flag per operation, or is it valid to send two flags at once?  That
is, can I send RAM_SAVE_FLAG_XBZRLE | RAM_SAVE_FLAG_HOOK on a single
packet?  Should we be flagging streams that send unexpected flag
combinations as invalid, even when each flag is in isolation okay,
rather than the current behavior of silently prioritizing one flag and
ignoring the other?

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


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