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List:       qemu-devel
Subject:    Re: [PATCH] migration: Yield coroutine when receiving MIG_CMD_POSTCOPY_LISTEN
From:       Peter Xu <peterx () redhat ! com>
Date:       2024-04-02 21:43:48
Message-ID: Zgx8FFzaFS1RsNmc () x1n
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On Tue, Apr 02, 2024 at 07:20:01AM +0000, Wang, Wei W wrote:
> > IIUC we still need that pre_7_2 stuff and keep the postponed connect() to
> > make sure the ordering is done properly.  Wei, could you elaborate the patch
> > you mentioned?  Maybe I missed some spots.
> 
> Sure. I saw your patch (5655aab079) ensures that the preempt channel to be
> created when PONG is received from the destination, which indicates that
> the main channel has been ready on the destination side.
> 
> Why was it decided to postpone the preempt channel's connect() for newer QEMU
> only? The old QEMU (before 7.2) still performs preempt channel connect() in
> migrate_fd_connect(), doesn't it have the disordering issue?

Yes it has, but the solution actually was not compatible with older
binaries, so migration was broken back then..  See:

https://lore.kernel.org/qemu-devel/20230326172540.2571110-1-peterx@redhat.com/

My memory was that we didn't have a good solution to fix it without
breaking the old protocol, so it can only be fixed on newer binaries.

Thanks,

-- 
Peter Xu


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