RE: linux shell comes out to qemu-monitor when I enter anything. (I have two uarts)

[Chan Kim]

Hi, Peter Maydell,

Thank you for the advice.
So I uncommented the stdio_in_use guard, and used this option
(because the second uart will be used)

-chardev null,mux=off,id=char0 -serial chardev:char0 -chardev 
stdio,mux=off,id=char1 -serial chardev:char1

And it gives me :
qemu-system-aarch64: cannot use stdio by multiple character devices

I tried setting mux=on or removing '-serial chardev:char0'. But the message is 
the same.
The only way I  can suppress the error seems to be removing the 'stdio_in_use' 
guard.
I don't know how to 'not connect anything' to my first UART.
Can you give me more specific option?

p.s. : by the way I'm running from u-boot-spl (using -kernel elf at 0x4000000) 
which jumps to loaded linux(by -device loader option at 0x80200000)
with dtb at 0x80000000 (also using -device loader option). 
I think in this case only my loaded dtb is used and the qemu-generated fdt is 
not used at all, is this correct?

Best regards,
Chan Kim

>-----Original Message-----
>From: Peter Maydell <peter.maydell@linaro.org>
>Sent: Wednesday, July 20, 2022 7:44 PM
>To: Chan Kim <ckim@etri.re.kr>
>Cc: qemu-discuss <qemu-discuss@nongnu.org>
>Subject: Re: linux shell comes out to qemu-monitor when I enter anything.
>(I have two uarts)
>
>On Wed, 20 Jul 2022 at 11:27, Chan Kim <ckim@etri.re.kr> wrote:
>>
>> Hello qemu experts,
>>
>> In my virtual machine I have two uart and I want to use the
>> input/output in my host machine.
>> For that I commented out these lines in qemu_chr_open_stdio function
>> in chardev/char-stdio.c. (qemu-6.2.0)
>>
>> /*
>> if (stdio_in_use) {
>>         error_setg(errp, "cannot use stdio by multiple character devices");
>>         return;
>>     }
>> */
>
>Don't do that, there is a reason why that guard is there.
>If you want multiple chardevs connecting to stdio you need to multiplex
>them (otherwise, which one should input from the terminal go to?).
>
>> And used this option for stdio.
>>
>> -chardev stdio,mux=on,id=char0 -serial chardev:char0 -serial
>> chardev:char0
>>
>> And two serial ports are generated and is multiplexed into stdio backend.
>> Actually in the software on the virtual machine, the first uart is
>> never written and only the second uart is written to. But the dtb
>> contains two uarts so I had to generate two frontends anyway.
>
>If you don't care about one of the UARTs, then just don't connect a chardev
>to it (or equivalently, connect an instance of the 'null' chardev, which
>throws away anything sent to it).
>
>-- PMM