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[Qemu-devel] Re: [PATCH] char: Flush read buffer in mux_chr_can_read


From: Alexander Graf
Subject: [Qemu-devel] Re: [PATCH] char: Flush read buffer in mux_chr_can_read
Date: Fri, 14 May 2010 18:00:44 +0200

On 12.05.2010, at 20:51, Jan Kiszka wrote:

> Alexander Graf wrote:
>> Jan Kiszka wrote:
>>> Alexander Graf wrote:
>>> 
>>>> Jan Kiszka wrote:
>>>> 
>>>>> Move the buffer flush from mux_chr_read to mux_chr_can_read. While the
>>>>> latter is called periodically, the former will only be invoked when new
>>>>> characters arrive at the back-end. This caused problems to front-end
>>>>> drivers whenever they were unable to read data immediately, e.g.
>>>>> virtio-console attached to stdio.
>>>>> 
>>>>> 
>>>> I don't see this patch applied, but also don't see any issues with
>>>> virtio-console anymore on today's git. Odd.
>>>> 
>>>> 
>>> Hmm, I had a clear before-after experience using virtio console with an
>>> x86 Linux guest. I still think my patch is correct and required. Maybe
>>> you can bisect this positive "regression"? Something might paper over
>>> the core issue now.
>>> 
>> 
>> I just did a git reset --hard on
>> baf0b55a9e57b909b1f8b0f732c0b10242867418 and it worked! What the ...
> 
> Whatever "worked" now means (I'm slightly confused), I just rechecked
> the situation over current git head ("qemu linux-guest.img -chardev
> stdio,id=cons,mux=on -device virtio-serial -device
> virtconsole,chardev=cons -mon chardev=cons", "cat /dev/hvc0" in the
> guest, typing some chars on the host console): The problem still
> persists, my patch still solves it. Can you confirm this, ideally also
> for s390?

Now that I can finally reproduce the bug with --enable-io-thread, I can verify 
that it does *not* fix the issue.

Alex




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