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Re: [Qemu-trivial] [Qemu-devel] [PATCH] qemu-char: fix terminal crash wh

From: Li Liu
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] qemu-char: fix terminal crash when using "-monitor stdio -nographic"
Date: Tue, 9 Sep 2014 10:22:26 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.4.0

On 2014/9/5 17:31, Gerd Hoffmann wrote:
> On Fr, 2014-09-05 at 11:04 +0200, Markus Armbruster wrote:
>> Li Liu <address@hidden> writes:
>>> Ping, any more comments? Thanks.
>> I'd like to hear Gerd's opinion (cc'ed).
>>>>> But is having multiple character devices use the same terminal valid?
> No (guess we should catch that case in stdio init).
> Beside the tty initialization and cleanup you also have the problem that
> both users are racing for input.  Well, maybe not in the qemu case as it
> is the same process and it very well might be that it polls the two
> chardevs in a well defined order, so one of them gets all input and the
> other gets nothing.  With two processes reading from the terminal (try
> 'cat | less') it is actually random though.
>>>> I'm not sure. But I have found such comments in vl.c
>>>> "According to documentation and historically, -nographic redirects
>>>> serial port, parallel port and monitor to stdio"
> In that case mux chardev is used (that is the piece which handles the
> input switching between serial and monitor via 'Ctrl-A c').  There is
> one stdio instance, and one mux instance, the mux is chained to stdio,
> and mux allows multiple backends to connect.
> You can construct it on the command line this way:
> qemu -nographic -nodefaults \
>    -chardev stdio,mux=on,id=terminal \
>    -serial chardev:terminal \
>    -monitor chardev:terminal
> [ serial is default, so no output here, unless you boot a guest
>   with serial console configured ]
> [ Hit 'Ctrl-A h' now ]
> C-a h    print this help
> C-a x    exit emulator
> C-a s    save disk data back to file (if -snapshot)
> C-a t    toggle console timestamps
> C-a b    send break (magic sysrq)
> C-a c    switch between console and monitor
> C-a C-a  sends C-a
> [ Hit 'Ctrl-A c' now ]
> QEMU 2.1.50 monitor - type 'help' for more information
> (qemu) info chardev
> terminal: filename=mux
> terminal-base: filename=stdio
> (qemu) 
> HTH,
>   Gerd

Appreciate your detailed answer. Thank you very much.


> .

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