Re: [Qemu-devel] Dummy question for setting up a serial connection between host and guest

[Markus Armbruster]

Christopher Covington <address@hidden> writes:

> Hi Alex,
>
> On 03/10/2015 09:12 PM, Alex Sun wrote:
>> I downloaded QEMU 2.2.0, and built a qemu-system-arm from there.
>> I loaded a versatile kernel 2.6.32.5 and my own file system.
>> 
>> #qemu-system-arm -pidfile /tmp/qemu_0_pids/0.pid -M versatilepb -option-rom
>> efi-rtl8139.rom -initrd newinitrd -kernel vmlinuz-2.6.32-5-versatile -append
>> "root=/dev/sda1 console=ttyAMA0" -hda new.qcow2 -drive file=fat:rw:./data
>> -nographic -no-reboot
>> 
>> I see following message while the kernel is booting:
>> 
>> [    3.873429] dev:f1: ttyAMA0 at MMIO 0x101f1000 (irq = 12) is a AMBA/PL011
>> [    3.884631] console [ttyAMA0] enabled
>> [    3.889783] dev:f2: ttyAMA1 at MMIO 0x101f2000 (irq = 13) is a AMBA/PL011
>> [    3.890646] dev:f3: ttyAMA2 at MMIO 0x101f3000 (irq = 14) is a AMBA/PL011
>> 
>> I think the serial ports of ttyAMA[0-2] are enabled.
>> Then I try to do serial redirection:
>> 
>> #qemu-system-arm -pidfile /tmp/qemu_0_pids/0.pid -M versatilepb -option-rom
>> efi-rtl8139.rom -initrd newinitrd -kernel vmlinuz-2.6.32-5-versatile -append
>> "root=/dev/sda1 console=ttyAMA0" -hda new.qcow2 -drive file=fat:rw:./data
>> -nographic -no-reboot *-serial stdio -serial pty*
>>
>> However, I get error message:
>> QEMU 2.2.0 monitor - type 'help' for more information
>> *(qemu) qemu-system-arm: -serial stdio: cannot use stdio by multiple 
>> character
>> devices*
>> 
>> It's weired to me. I don't think there is another one other than qemu itself
>> holding the stdio. 

You can connect multiple users to a character device in multiplexing
mode.  Quoting the fine manual:

    A character device may be used in multiplexing mode by multiple
    front-ends.  The key sequence of @key{Control-a} and @key{c} will
    rotate the input focus between attached front-ends. Specify
    @option{mux=on} to enable this mode.

> I think the conflict is that when you specify -nographic, the QEMU monitor
> uses stdio. I find it necessary to add "-monitor none" to all of my
> command lines.

I use -nodefault.  One stone, many annoying birds.