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

[Jason Vas Dias]

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
>