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[Qemu-devel] Re: [PATCH 09/21] Introduce event-tap.
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] Re: [PATCH 09/21] Introduce event-tap. |
Date: |
Tue, 30 Nov 2010 10:04:08 +0000 |
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).
> 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?
Stefan