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Re: [PATCH RFC 0/3] mirror: rework soft-cancelling READY mirror

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH RFC 0/3] mirror: rework soft-cancelling READY mirror
Date: Thu, 29 Jul 2021 13:02:13 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0

28.07.2021 10:00, Max Reitz wrote:
On 27.07.21 18:47, Vladimir Sementsov-Ogievskiy wrote:
Hi all!

That's an alternative to (part of) Max's
"[PATCH for-6.1? v2 0/7] mirror: Handle errors after READY cancel"
and shows' my idea of handling soft-cancelling READY mirror case
directly in qmp_block_job_cancel. And cleanup all other job cancelling

That's untested draft, don't take it to heart :)

Well, I would have preferred it if you’d rebased this on top of that series, 
precisely because it’s an alternative to only part of it. And if it’s just an 
untested draft, that would have been even better, because it would’ve given a 
better idea on what the cleanup looks like.

There are also things like this series making cancel internally always a 
force-cancel, where I’m not sure whether we want that in the replication driver 
or not[1].  With my series, we add an explicit parameter, so we’re forced to 
think about it, and then in this series on top we can just drop the parameter 
for all force-cancel invocations again, and for all non-force-cancel 
invocations we would have to think a bit more.

I now don't sure that patch 5 of your series is correct (see my last answer to 
it), that's why I decided to not base on it. My series has the benefit of 
handling soft-mirror-cancel case the other way and handles mirror finalization 
in case of soft-cancel properly.

Specifically as for this series, I don’t like job_complete_ex() very much, I 
think the parameter should be part of job_complete() itself.

That was my idea. But job_complete is passed as function pointer, so changing 
its prototype would be more work.. But I think it's possible.

  If we think that’s too specific of a mirror parameter to include in normal 
job_complete(), well, then there shouldn’t be a job_complete_ex() either, and 
do_graph_change should be a property of the mirror job (perhaps as 
pivot_on_completion) that’s cleared by qmp_block_job_cancel() before invoking 

This way users will lose a way to make a decision during job running.. But 
probably they don't need actually. Moving the option to mirror job parameter 
seems a good option to me.


[1] Although looking at it again now, it probably wants force-cancel.

What do you think of my idea to keep old bugs as is and just deprecate block-job-cancel 
and add a new interface for "no-graph-change mirror" case?

Best regards,

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