Re: Priority of -accel

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On Tue, Jan 7, 2020 at 1:34 PM Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> 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

I meant "more explicit" =)