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[Qemu-devel] Re: [PATCH 09/21] Introduce event-tap.
From: |
Yoshiaki Tamura |
Subject: |
[Qemu-devel] Re: [PATCH 09/21] Introduce event-tap. |
Date: |
Tue, 30 Nov 2010 19:20:08 +0900 |
2010/11/30 Stefan Hajnoczi <address@hidden>:
> On Tue, Nov 30, 2010 at 9:50 AM, Yoshiaki Tamura
> <address@hidden> wrote:
>> 2010/11/29 Stefan Hajnoczi <address@hidden>:
>>> On Thu, Nov 25, 2010 at 6:06 AM, Yoshiaki Tamura
>>> <address@hidden> wrote:
>>>> event-tap controls when to start FT transaction, and provides proxy
>>>> functions to called from net/block devices. While FT transaction, it
>>>> queues up net/block requests, and flush them when the transaction gets
>>>> completed.
>>>>
>>>> Signed-off-by: Yoshiaki Tamura <address@hidden>
>>>> Signed-off-by: OHMURA Kei <address@hidden>
>>>> ---
>>>> Makefile.target | 1 +
>>>> block.h | 9 +
>>>> event-tap.c | 794
>>>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>> event-tap.h | 34 +++
>>>> net.h | 4 +
>>>> net/queue.c | 1 +
>>>> 6 files changed, 843 insertions(+), 0 deletions(-)
>>>> create mode 100644 event-tap.c
>>>> create mode 100644 event-tap.h
>>>
>>> event_tap_state is checked at the beginning of several functions. If
>>> there is an unexpected state the function silently returns. Should
>>> these checks really be assert() so there is an abort and backtrace if
>>> the program ever reaches this state?
>
> Fancier error handling would work too. For example cleaning up,
> turning off Kemari, and producing an error message with
> error_report(). In that case we need to think through the state of
> the environment carefully and make sure we don't cause secondary
> failures (like memory leaks).
Turning off Kemari should include canceling the transaction which
notifies the secondary. So same as you commented for
ft_trans_file error handling, I would implement better handling
for event-tap again.
>> BTW, I would like to ask a question regarding this. There is a
>> callback which net/block calls after processing the requests, and
>> is there a clean way to set this callback on the failovered
>> host upon replay?
>
> I think this is a limitation in the current design. If requests are
> re-issued by Kemari at the net/block level, how will the higher layers
> know about these requests? How will they be prepared to accept
> callbacks?
That's why we're using pio/mmio replay at this moment. With a
dirty hack in device emulators setting callbacks before replay,
block/net replay seems to work, but I don't think that to be a
correct solution.
Yoshi
>
> Stefan
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