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Re: [Qemu-devel] [PATCH 2/7] migration: only flush when there are no err

From: Juan Quintela
Subject: Re: [Qemu-devel] [PATCH 2/7] migration: only flush when there are no errors
Date: Tue, 20 Sep 2011 16:47:38 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)

"Daniel P. Berrange" <address@hidden> wrote:
> On Tue, Sep 20, 2011 at 03:24:41PM +0200, Juan Quintela wrote:
>> If we have one error while migrating, and then we issuse a
>> "migrate_cancel" command, guest hang.  Fix it for flushing only when
>> migration is in MIG_STATE_ACTIVE.  In case of error of cancellation,
>> don't flush.
>> We had an infinite loop at buffered_close()
>>         while (!s->has_error && s->buffer_size) {
>>             buffered_flush(s);
>>             if (s->freeze_output)
>>                 s->wait_for_unfreeze(s);
>>         }
>> There was no errors, there were things to send, and connection was
>> broken.  send() returns -EAGAIN, so we freezed output, but we
>> unfreeze_output and try again.
> I posted a couple of alternative approaches to fixing this
> hang problem
> http://lists.nongnu.org/archive/html/qemu-devel/2011-08/msg03248.html
> My second approach of checking the migration state in migrate_fd_put_buffer()
> seems like it would be worthwhile, even with your patch as an additional
> safety net against bad code.

We can add that there, but in my tests, the s->write() was returning
correctly an error (or -EAGAIN).  The problem was that we were not
exiting when we didn't needed to.

I agree that we can have *both* tests.  I will add your patch to my

Thanks for the fast review.

Later, Juan.

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