[libvirt-users] use of qemu-kvm --chardev pipe, id=X, path=... argument ?

[Jason Vas Dias]

OK, solved this one myself (sort of) :
 o Using the command line options:
    ... -append 'root=/dev/sda rw selinux=0 enforcing=0 console=ttyS0'
-m 2048 -k en-gb -nographic -vga none -vnc none -enable-kvm -serial
stdio  -nodefaults

 does get the kernel to launch the console on stdio .

 So doing :
 $ qemu-kvm ...  -append 'root=/dev/sda rw selinux=0 enforcing=0
console=ttyS0' -m 2048 -k en-gb -nographic -vga none -vnc none
-enable-kvm -serial stdio  -nodefaults \
   <$MY_INPUT_PIPE >/tmp/$MY_OUPUT_PIPE 2>&1
does have exactly the effect I want . Hooray!
(where '...' are the other qemu-kvm arguments in quoted mail, and
$MY_*PIPE are /tmp/el6x32.in and /tmp/el6x32.out as in previous mail.

The above command works, so I can do:
   $ cat $MY_OUTPUT_PIPE &'
   $ cat >>$MY_INPUT_PIPE
and I get a login prompt.

But I still can't understand why this does not have the desired effect:
    $ qemu-kvm ...  -append 'root=/dev/sda rw selinux=0 enforcing=0
console=ttyS0' -m 2048 -k en-gb -nographic -vga none -vnc none
-enable-kvm -nodefault -chardev 'pipe,id=0,path=/tmp/el6x32'
No output is produced on the output pipe after connecting a writer
to the input pipe.

I'd like to understand how the '--chardev pipe,path=...' option is meant to
work if it does not have the effect of '-serial stdio' with I/O redirected
to the pipes.




On 05/01/2015, Jason Vas Dias <jason.vas.dias at gmail.com> wrote:
> Aha! Thank you.  Yes that does prevent the default stdio console .
> But no output appears on the input pipe, and outputting to input end has
> no effect:
> In one terminal, I do:
>   $ cat /tmp/el6x32.out
> in the main terminal, I run:
> $ /usr/libexec/qemu-kvm -M rhel6.4.0 -cpu n270 -smp 1 -hda
> /home/rpmbuild/OEL6/img/OEL6_32.img -kernel
> /home/rpmbuild/OEL6/boot/vmlinuz-2.6.39-400.215.14.el6uek.i686 -initrd
> /home/rpmbuild/OEL6/boot/initramfs-2.6.39-400.215.14.el6uek.i686.img
> -append 'root=/dev/sda rw selinux=0 enforcing=0 console=0' -m 2048 -k
> en-gb -nographic -vga none -vnc none -enable-kvm -chardev
> pipe,id=0,path=/tmp/el6x32 -chardev tty,id=1,path=/dev/pts/4 -monitor
> stdio -nodefaults
> QEMU 0.12.1 monitor - type 'help' for more information
> (qemu) info status
> VM status: running
> (qemu)
>
> In another terminal I connect to the input pipe:
>    $ cat >>/tmp/el632.in
>
> But no output appears on the /tmp/el6x32.out pipe ,
> regardless of what is typed on the input pipe .
>
> I want to issue the login commands and then set up the shell
> to run commands echo'ed to the input pipe on the physical - eg. :
>    $ echo 'ls' > /tmp/el6x32.in
> and read the output from the guest on the output pipe:
>    $ cat /tmp/el632.out
>
> Anyone know any way of doing this ?
>
> I'm trying to run a nested guest in a VMware guest whose physical host CPU
> has VMX enabled using qemu-kvm, but guest virtual networking is disabled
> in VMware  so I can't use ssh / telnet in the guest to run commands .
>
> Thanks for any further replies,
> Jason
>
> On 05/01/2015, Michal Privoznik <mprivozn at redhat.com> wrote:
>> On 05.01.2015 15:03, Jason Vas Dias wrote:
>>> Please can anyone enlighten me as to why linux qemu-kvm always
>>> creates the console on my terminal, when I am trying to direct
>>> all of its input and output to a pipe ?
>>>
>>> I have created :
>>>     $ mkfifo /tmp/el6x32{.in,.out,.monitor}
>>> and use the command:
>>>     $ /usr/libexec/qemu-kvm -M rhel6.4.0 -cpu n270 -smp 1 \
>>>       -hda /home/rpmbuild/OEL6/img/OEL6_32.img \
>>>       -kernel
>>> /home/rpmbuild/OEL6/boot/vmlinuz-2.6.39-400.215.14.el6uek.i686 \
>>>       -initrd /home/rpmbuild/OEL6/boot/initramfs
>>> 2.6.39-400.215.14.el6uek.i686.img \
>>>       -append 'root=/dev/sda rw selinux=0 enforcing=0 console=0' \
>>>       -m 2048 -k en-gb -nographic -vga none -vnc none -enable-kvm \
>>>       -chardev pipe,id=0,path=/tmp/el6x32 -monitor
>>> pipe:/tmp/el6x32.monitor
>>>
>>> But this ends up with the kernel's console on qemu-kvm's  STDIO .
>>>
>>> I actually want the console to be redirected to take input from
>>> /tmp/el6x32.in and direct output to /tmp/el6x32.out -
>>> I thought that was what the above '-chardev pipe,id=0,path=/tmp/el6x32'
>>> should do if kernel boot params 'console=0' is also supplied ?
>>> Why isn't this happening for me ? Anyone got a guest to read console
>>> input
>>> from a pipe and direct console output to a pipe ? If so, how?
>>>
>>> Thanks in advance for any replies, Jason.
>>
>> That's probably because qemu by default creates some
>> serial/parallels/virtual console/... You may want to pass '-nodefaults'
>> onto qemu-kvm command line.
>>
>> Michal
>>
>