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Re: [Qemu-devel] [PATCH 2/3] replay: allow replay stopping and restartin
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] replay: allow replay stopping and restarting |
Date: |
Wed, 29 Jun 2016 12:45:57 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 20/06/2016 08:26, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden
>>> From: "Pavel Dovgalyuk" <address@hidden>
>>> This patch fixes bug with stopping and restarting replay
>>> through monitor.
>>>
>>> Signed-off-by: Pavel Dovgalyuk <address@hidden>
>>> ---
>>> block/blkreplay.c | 18 +++++++++++++-----
>>> cpus.c | 1 +
>>> include/sysemu/replay.h | 2 ++
>>> replay/replay-internal.h | 2 --
>>> vl.c | 1 +
>>> 5 files changed, 17 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/block/blkreplay.c b/block/blkreplay.c
>>> index 42f1813..438170c 100644
>>> --- a/block/blkreplay.c
>>> +++ b/block/blkreplay.c
>>> @@ -70,6 +70,14 @@ static void blkreplay_bh_cb(void *opaque)
>>> g_free(req);
>>> }
>>>
>>> +static uint64_t blkreplay_next_id(void)
>>> +{
>>> + if (replay_events_enabled()) {
>>> + return request_id++;
>>> + }
>>> + return 0;
>>> +}
>>
>> What happens if 0 is returned?
>
> It could be any value. When replay events are disables,
> it means that either replay is disabled or execution is stopped.
> In first case we won't pass this requests through the replay queue
> and therefore id is useless.
> In stopped mode we have to keep request_id unchanged to make
> record/replay deterministic.
>
>> I think that you want to call
>> replay_disable_events...
>>
>>> bdrv_drain_all();
>>
>> ... after this bdrv_drain_all.
>
> Why? We disable replay events to avoid adding new block requests
> to the queue. How this is related to drain all?
drain all completes the guest's pending requests. If you disable events
before drain all, doesn't that cause a mismatch between record and replay?
>>
>> I was going to suggest using qemu_add_vm_change_state_handler
>> in replay_start (which could have replaced the existing call
>> to replay_enable_events), but that's not possible if you have
>> to do your calls after bdrv_drain_all.
>
> Pavel Dovgalyuk
>
>
>
[Qemu-devel] [PATCH 1/3] target-ppc: exceptions handling in icount mode, Pavel Dovgalyuk, 2016/06/08
[Qemu-devel] [PATCH 3/3] record/replay: add network support, Pavel Dovgalyuk, 2016/06/08