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[Qemu-devel] Re: [PATCH 2/3] char: Remove special init_reset handling

From: Jan Kiszka
Subject: [Qemu-devel] Re: [PATCH 2/3] char: Remove special init_reset handling
Date: Wed, 04 Nov 2009 15:30:21 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

Amit Shah wrote:
> On (Wed) Nov 04 2009 [10:39:39], Jan Kiszka wrote:
>> Amit Shah wrote:
>>> On (Tue) Nov 03 2009 [19:53:43], Jan Kiszka wrote:
>>>> Amit Shah wrote:
>>>>> On (Tue) Nov 03 2009 [23:25:52], Amit Shah wrote:
>>>>>> On (Tue) Nov 03 2009 [18:08:57], Jan Kiszka wrote:
>>>>>>> Amit Shah wrote:
>>>>>>>> The initial_reset sent to chardevs doesn't do much other than setting
>>>>>>>> a bool to true. Char devices are interested in the open event and
>>>>>>>> that gets sent whenever the device is opened.
>>>>>>> Have you checked with the monitor in all use cases (dedicated & muxed
>>>>>>> console, stdio & SDL console, etc.)? It was introduced once to fix a
>>>>>> I've checked with -monitor stdio, monitor in SDL and also chardevs using
>>>>>> unix sockets.
>>>>>> I've not tried mux yet; I'll try that and report back. BTW if it ends up
>>>>>> not working with this patch, it'd be broken in the current master as
>>>>>> well.
>>>>> I tried with:
>>>>> -chardev stdio,mux=on,id=mux -monitor chardev:mux -serial chardev:mux
>>>>> The monitor prompt shows up as does the serial output.
>>>>> (btw I've also tried closing and opening char devs and that works fine
>>>>> too)
>>>> That sounds good. Then something must have changed since 2970a6c943, do
>>>> you see what?
>>> I think that depended on the resets being sent. I've now removed the
>>> need for resets altogether.
>> No, this is in fact the reason why we no longer need it:
>>      9a1e948129 (Introduce contexts for asynchronous callbacks)
>> As the initial reset of the char device that is marked pending on open
>> is now no longer consumed by the IDE initialization, we can actually
>> drop the later regeneration via qemu_chr_initial_reset. I just hope this
>> stays like it is...
> I tested this even on a tree that doesn't have this patch.

The whole things was (and maybe still is) fragile. So you have to take
care what further patches with side effects you include. If you revert
9a1e948129 and remove qemu_chr_initial_reset, you get the old bug back
again, ie. no prompt.

> I haven't really delved deep to see why this was added earlier -- the
> commit log only says very little. Plus my testing with the current tree
> works fine so I'm happy to mention these things in the commit log.

I've nothing against your patch, specifically as it removes an obviously
no longer needed workaround, not a feature. I just want to make sure
that the current behavior is not only there by chance.


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