Re: [Qemu-devel] [PATCH RFC] qemu-char: add logfile facility to socket backend

[Paolo Bonzini]

On 17/12/2015 12:55, Daniel P. Berrange wrote:
> Typically a UNIX guest OS will log boot messages to a serial
> port in addition to any graphical console. An admin user
> may also wish to use the serial port for an interactive
> console. A virtualization management system may wish to
> collect system boot messages by logging the serial port,
> but also wish to allow admins interactive access.
> 
> Currently providing such a feature forces the mgmt app
> to either provide 2 separate serial ports, one for
> logging boot messages and one for interactive console
> login, or to proxy all output via a separate service
> that can multiplex the two needs onto one serial port.
> While both are valid approaches, they each have their
> own downsides. The former causes confusion and extra
> setup work for VM admins creating disk images. The latter
> places an extra burden to re-implement much of the QEMU
> chardev backends logic in libvirt or even higher level
> mgmt apps and adds extra hops in the data transfer path.
> 
> A simpler approach that is satisfactory for many use
> cases is to allow the QEMU chardev backends to have a
> "logfile" property associated with them.
> 
>  $QEMU -chardev socket,host=localhost,port=9000,\
>                 server=on,nowait,id-charserial0,\
>               logfile=/var/log/libvirt/qemu/test-serial0.log
>        -device isa-serial,chardev=charserial0,id=serial0

Why for socket only?  It would be very useful for stdio and especially vc.

Paolo