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

[Daniel P. Berrange]

On Thu, Dec 17, 2015 at 01:00:41PM +0100, Paolo Bonzini wrote:
> 
> 
> 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.

This is just an "RFC" so didn't want to spend the time to wire
up all of them until I got positive feedback on the idea :-)
If its acceptable, then I think it could make sense to just
support optional "logfile" on every single backend, except "file"

Regards,
Daniel
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