[Qemu-devel] restart a coroutine?

[Michael Tokarev <mjt@tls.msk.ru>]

Since all block (bdrv) layer is now implemented using
coroutines, I thought I'd give it a try.  But immediately
hit a question to which I don't know a good answer.

Suppose we've some networking block device (like NBD) and
want to be able to support reconnection - this is actually
very useful feature, in order to be able to reboot/restart
the NBD server without a need to restart all the clients.

For this to work, we should have an ability to reconnect
to the server and re-issue all requests which were waiting
for reply.

Traditionally, in asyncronous event-loop-based scheme, this
is implemented as a queue of requests linked to the block
driver state structure, and in case of reconnection we just
walk over all requests and requeue these.

But if the block driver is implemented as a set of coroutines
(like nbd currently does), I see no sane/safe way to restart
the requests.  Setjmp/longjmp can be uses with extra care
there, but with these it is extremly fragile.

Any hints on how to do that?

Thanks,

/mjt