[libvirt-users] Libvirt-QEMU : Multiplex the output from qemu's serial port to a pty as well as a file (basically redirect console to file as well as pty device)

[gokul cg]

Hi All,

I could following documentation ,
https://wiki.libvirt.org/page/LibvirtConsoleManagement
I hope this doc is upto date , as of now there is no way other than
conserver. Please let me know if there is any alternative.
LibvirtConsoleManagement (doc snippet pasted from above link)
----------------------------------------------------------
This page describes an approach to managing virtual machine text consoles,
which leverages the conserver daemon
Background information

With Xen, LXC, KVM, etc hypervisors there is typically a serial console or
a paravirtualized log for each virtual machine. Typically this is exposed
on the host as a dynamically allocated psuedo TTY, but they can also be
configured to use a UNIX or TCP socket, a FIFO pipe or (output only) to a
plain file.

The consoles are typically used as a text-mode interactive shell, or to log
all guest console messages, or both. There are a number of limitations with
the console functionality that is exposed natively by the hypervisors

   - It is impossible to configure a console to both provide an interactive
   pTTY, and log all data to a file concurrently.
   - If configured to log to a file, the file will grow without any bounds
   - The console TTY names are unstable across restarts of the virtual
   machine, since they are dynamically allocated by the host kernel
   - The console TTYs only exist while the VM is running
   - There is typically no native, secure, remote TCP access

Architecture design

The problems described with the native hypervisor console configuration can
broadly be addressed by leveraging the conserver daemon, which is
distributed as a standard part of most Linux distributions. The main
integration pain point is that the conserver daemon uses a static
configuration file, while virtual machines can come & go at any moment.

There is a need, therefore, to have a way of automatically
generating/updating the conserver configuration file on the fly to deal
with dynamic virtual machines. This can be achieved by having a process
which listens out for libvirt domain lifecycle events and triggers an
update of the conserver configuration file at appropriate times.

Regards
Gokul

On Fri, Oct 11, 2019 at 12:20 PM gokul cg <gokuljnpr at gmail.com> wrote:

> +dev
> Hi Folks ,
>
> As per https://libvirt.org/formatdomain.html#elementsConsole
> Regardless of the type, character devices can have an optional log file
> associated with them.
> Whether the lgging functionality is same as mapping device to file ?
> Whether libvirt xml syntax below both 1 and 2 are same ?
>
>     1)
>     <serial type='pty'>
>       <log
> file='/var/lib/nova/instances/7151c8b7-1ea5-4701-bb79-b482d9e253b8/console.log'
> append='off'/>
>       <target port='0'/>
>     </serial>
>
>     2)
>     <serial type='pty'>
>       <source path='/tmp/serial.log'/>
>       <target port='0'/>
>     </serial>
>
>     is it possible to multiplex the output from qemu's serial port  to a
> pty as well as a file (basically redirect console to file as well as pty
> device)?
>
> Regards
> Gokul
>
>
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