Re: [Qemu-devel] [PATCH v7 04/19] replay: don't drain/flush bdrv queue while RR is working

[Kevin Wolf]

Am 10.10.2018 um 15:33 hat Pavel Dovgalyuk geschrieben:
> In record/replay mode bdrv queue is controlled by replay mechanism.
> It does not allow saving or loading the snapshots
> when bdrv queue is not empty. Stopping the VM is not blocked by nonempty
> queue, but flushing the queue is still impossible there,
> because it may cause deadlocks in replay mode.
> This patch disables bdrv_drain_all and bdrv_flush_all in
> record/replay mode.
> 
> Signed-off-by: Pavel Dovgalyuk <address@hidden>

Disabling bdrv_flush_all() shouldn't make a big difference in replay
mode, so I agree with that.

But does the bdrv_drain_all() change mean that bdrv_drain_all_begin()
can return while there are still requests in flight? This sounds like
something that could break some existing code, because the meaning of
the function is that if it returns success, no requests are in flight
any more.

What would move the request forward in the replay case once it has been
created? Does this also involve some user interaction? Or may we process
the next event in a drain callback of blkreplay or something?

Kevin