Re: [Qemu-devel] [PATCH 1/4] Replace '-machine accel=xyz' with '-accel xyz'

[Eduardo Habkost <ehabkost@redhat.com>]

On Wed, Jun 13, 2018 at 02:53:04PM +0200, Thomas Huth wrote:
> On 13.06.2018 14:48, Paolo Bonzini wrote:
> > On 13/06/2018 07:05, Thomas Huth wrote:
> >> diff --git a/tests/vmgenid-test.c b/tests/vmgenid-test.c
> >> index 8d915c6..4324034 100644
> >> --- a/tests/vmgenid-test.c
> >> +++ b/tests/vmgenid-test.c
> >> @@ -131,7 +131,7 @@ static void read_guid_from_monitor(QemuUUID *guid)
> >>  static char disk[] = "tests/vmgenid-test-disk-XXXXXX";
> >>  
> >>  #define GUID_CMD(guid)                          \
> >> -    "-machine accel=kvm:tcg "                   \
> >> +    "-accel kvm:tcg "                           \
> >>      "-device vmgenid,id=testvgid,guid=%s "      \
> > 
> > "-accel kvm:tcg" works, but it really shouldn't (and I think we can
> > change it without a deprecation period).   The right syntax would be
> > "-accel kvm -accel tcg", so that you can specify options that are valid
> > only for KVM, or onlty for TCG.
> 
> I see your point, but this would break these qtests that are trying to
> override the "-machine accel=qtest" from libqtest.c this way... and if
> any other tool out there in the wild is already depending on this
> behavior, too, we can not change it so easily anymore.

Tools might rely in "-machine accel=kvm:tcg", but I don't think
anybody should be relying on "-accel kvm:tcg" to work.

I agree with Paolo.  If "-accel kvm:tcg" works today, I think we
should either remove that behavior immediately, or deprecate it
on QEMU 3.0.

We should also make sure "-accel kvm,FOO=BAR -accel tcg" won't
set FOO=BAR in the TCG accelerator if KVM is unavailable.

-- 
Eduardo