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Re: [PATCH 2/2] nbd: requeue command if the soecket is changed

On 03/03/2020 04:06 PM, Mike Christie wrote:
> On 03/03/2020 03:13 PM, Josef Bacik wrote:
>> On 2/28/20 1:40 AM, Hou Pu wrote:
>>> In commit 2da22da5734 (nbd: fix zero cmd timeout handling v2),
>>> it is allowed to reset timer when it fires if tag_set.timeout
>>> is set to zero. If the server is shutdown and a new socket
>>> is reconfigured, the request should be requeued to be processed by
>>> new server instead of waiting for response from the old one.
>>> Signed-off-by: Hou Pu <houpu@bytedance.com>
>> I'm confused by this, if we get here we've already timed out and
>> requeued once right?  Why do we need to requeue again?  Thanks,
> We may not have timed out already. If the tag_set.timeout=0, then the
> block timer will fire every 30 seconds. This could be the first time the
> timer has fired. If it has fired multiple times already then it still
> would not have been requeued because the num_connections=1 code just
> does a BLK_EH_RESET_TIMER when timeout=0 and does not have support for
> detecting reconnects.
> In this second patch if timeout=0 and num_connections=1 we restart the
> command when the command timer fires and we detect a new connection
> (nsock->cookie has incremented).
> I was saying in the last patch, maybe waiting for reconnect is wrong.
> Does a cmd timeout=0 mean to wait for a reconnect or in this patch
> should we do:
> 1. if timeout=0, num_connections=1, and the cmd timer fires and the
> conneciton is marked dead then requeue the command.
> 2. we then rely on the dead_conn_timeout code to decide how long to wait
> for a reconnect.

Oh yeah, I had thought Hou implemented timeout=0 to wait for a reconnect
to handle existing apps. However, I am not sure if they exist. When we
had timeout=0 support the first time then we did not have multi conn and
reconnect support yet.

The current timeout=0 and reconnect support does not work since that is
what Hou is implementing, so we can decide the behavior now.

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