Re: [Qemu-devel] ivshmem property size should be a size, not a string

[Markus Armbruster <armbru@redhat.com>]

Marc-André Lureau <mlureau@redhat.com> writes:

> Hi
>
> ----- Original Message -----
>> >
>> > You can't migrate the peers.
>> 
>> Then explain the case N'=0 to me: how can you migrate the master so that
>> it's connected to a server afterwards?
>
> Dest qemu: -incoming.. -chardev socket,path=dest-server 
>
> That is, start your destination qemu with a destination server. The master
> origin qemu will migrate the shared memory, and the dest memory will be sync
> when the migration is done.

Got it!

>> > It works fine in the tests. Feel free to point out races or other issues.
>> 
>> I think I did: doorbell detection is inherently racy.
>> 
>> If you think it isn't, please refute my reasoning.
>
> I gave you some clues on how I did it in ivshmem-test.c: waiting for a
> signature on the memory to be mapped (and also checking that peers
> received ids)
>
>> If it's not broken, please explain to me how the guest should find out
>> whether its ivshmem device sports a doorbell.
>
> If you have received ID, you should be good to use the doorbell.

That's not a complete answer, so let me try a different tack.

What value will a read of register IVPosition yield

* if the device has no doorbell:

  I think the answer is -1.

* if the device has a doorbell, but it isn't ready, yet:

  I think the answer is -1.

* if the device has a doorbell, and it is ready.

  This is the part you answered already: >= 0.

Please correct mistakes.