[Qemu-devel] Re: [PATCH 33/41] virtio-net: port to vmstate

[Juan Quintela]

"Michael S. Tsirkin" <address@hidden> wrote:
> On Wed, Dec 02, 2009 at 07:38:03PM +0100, Juan Quintela wrote:
>> "Michael S. Tsirkin" <address@hidden> wrote:

> I expect it fits in practice.
> But you should range check the value and fail migration on error.
>
>>  That is only
>> needed for old versions that we are reading (get_* function has real
>> code).  But we are supposed to never write old versions (*).
>> Thet that shouldn't happen ever.
>
> vmstate guarantees this won't be called?

No, I express it badly.  That function should never be called.  It is a
compatibility type for old versions.  Only get() part should be used.
What should be guaranteed is that you protect that with a test or
something to assure that only the get() part is ever used, not the put()
one.

> So just assert(1)? Let's not write a ton of
> code that isn't called?

options are:
a- put a NULL value in the struct, and if there are ever an error get a
   segmentation fault.
b- put a function that just writes "the impossible happened in <foo>"
   and exit.

I don't know where do you want me to put one assert.

Later, Juan.

>> >  when
>> > is this called? Please supply a comment.
>> > Maybe call assert?
>> >
>> 
>> assert or exit is ok for me, what does people preffer?
>> 
>> Later, Juan.
>> 
>> (*): My next series will propose to change that and allow to write old
>>      versions, but that didn't exist when this code was written, and
>>      there are still no agreement about how/if doing it.