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

[Eric Blake]

On 06/10/2014 06:55 AM, Eric Blake wrote:
> 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.
>>

>>          } 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?

For that matter, would it be better to change the if-tree into a switch,
so that the default case catches unsupported combinations?

switch (flags) {
  ...
  case RAM_SAVE_FLAG_HOOK: ...
  case RAM_SAVE_FLAG_EOS: ...
  default: report unsupported flags value
}

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

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