Re: Priority of -accel

[Philippe Mathieu-Daudé]

On 1/7/20 1:18 PM, Thomas Huth wrote:
> On 07/01/2020 11.14, Paolo Bonzini wrote:
> > On 07/01/20 11:03, Thomas Huth wrote:
> > > >   
> > > >   vm = QEMUMachine(iotests.qemu_prog)
> > > > -vm.add_args('-machine', 'accel=kvm:tcg')
> > > > +vm.add_args('-accel', 'kvm', '-accel', 'tcg')
> > > Looking at this, I wonder whether we really want the "-accel" option to
> > > prioritize the accelerators in the order of appearance? A lot of other
> > > CLI tools give the highest priority to the last parameter instead, e.g.
> > > "gcc -O3 -O1" compiles with -O1, and not with -O3.
> > >
> > > Also I think it might be quite common that there are shell scripts which
> > > call "qemu-system-xxx -accel xyz $*" ... and if we don't invert the
> > > priorities of -accel, it will be impossible to override -accel in that
> > > case...
> >
> > Hmm, it does match "-machine accel=kvm:tcg" and in general I think it's
> > more self-explanatory.  However, it is indeed less friendly to scripts.
> >   On one hand those could be changed to place "-accel xyz" after $* (or
> > better "$@"), on the other hand we could also add a priority option to
> > "-accel".  What do you think?
>
> I don't think we need a separate priority parameter here. But IMHO it's
>   really rather common practice to prioritize the last option. So while
> it might be more "self-explanatory" to a CLI newbie if the first
> occurrence got the highest priority, it might be rather confusing
> instead for a CLI veteran...?
>
> What do others on the list here think about this?

We can make CLI more complex by adding a 'priority' option:

  -accel tcg,priority=1 -accel kvm,priority=0