linux-aio: track whether the queue is blocked

linux-aio: track whether the queue is blocked

Avoid that unplug submits requests when io_submit reported that it
couldn't accept more; at the same time, try more io_submit calls if it
could handle the whole set of requests that were passed, so that the
"blocked" flag is reset as soon as possible.

After the previous patch, laio_submit already tried to avoid submitting
requests to a blocked queue, by comparing s->io_q.idx with "==" instead
of the more natural ">=".  Switch to the simpler expression now that we
have the "blocked" flag.

Signed-off-by: Paolo Bonzini <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Message-id: 1418305950[email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>