Re: [Qemu-devel] [PATCH 03/10] target-i386: move hyperv_* static globals to CPUState

[Eduardo Habkost]

On Tue, Feb 26, 2013 at 06:10:25PM +0100, Igor Mammedov wrote:
> On Tue, 26 Feb 2013 14:06:05 -0300
> Eduardo Habkost <address@hidden> wrote:
> 
> > On Tue, Feb 26, 2013 at 05:39:02PM +0100, Igor Mammedov wrote:
> > [...]
> > > > > > > > * I don't expect hv-* to appear on a machine-type compat_props
> > > > > > > > array in the near feature.
> > > > > > > > * I don't expect people to need to set per-CPU hv-* properties
> > > > > > > > on device_add for CPU hotplug.
> > > > > > > > 
> > > > > > > > So we could keep them as special cases on parse_featurestr(),
> > > > > > > > and convert them to per-CPU properties only after we have the
> > > > > > > > subclasses and CPU hotplug working.
> > > > > > > it won't be a consistent interface, where user who has 
> > > > > > > "-cpu XXX,+foo1,+hv_spinlocks,+foo2" on cmd-line
> > > > > > > would have to use "device_add XXX,foo1=true,foo2=true" manually
> > > > > > > excluding options from device_add, i.e. it propagates special
> > > > > > > casing to users as well. And when hv_ are moved to per-CPU
> > > > > > > fields, it might break users since they will still exclude some
> > > > > > > options.
> > > > > > 
> > > > > > Won't -cpu/parse_featurestr() simply set global properties? In this
> > > > > > case, the common case would be to call "device_add XXX" with no
> > > > > > extra options at all, so there's no option to be excluded and no
> > > > > > special case to care about.
> > > > > That is if global properties will made to 1.5  which I highly doubt
> > > > > taking in account how fast patches are reviewed and accepted.
> > > > > Otherwise release would be broken. 
> > > > 
> > > > IMO it _has_ to make 1.5 and is a requirement to make device_add usable
> > > > for CPU hotplug. Otherwise we would have to change the behavior of -cpu
> > > > + device_add in an incompatible way.
> > > if all -cpu features are converted to static properties, we do not have to
> > > have global properties working. In absence of 'global properties', user
> > > will have to use the same properties at device_add that was specified at
> > > -cpu. And introduction of global properties won't regress it, it will
> > > just allow to use device_add without features specified on -cpu
> > 
> > Strictly, we do not have to, but changing -cpu to set global properties
> > only later would change the behavior of "-cpu XXX,foo=1,bar=2" followed
> > by "device_add XXX" in an incompatible way. So if our long-term plan is
> Could you explain how ^^^ it will be incompatible, pls?

Suppose that "foo" defaults to 0, and we run: "-cpu XXX,foo=1", followed
by "device_add XXX".

Without globals/defaults set by -cpu, the above will create a new CPU
with foo=0.

With globals/defaults set by -cpu, the above will create a new CPU with
foo=1.

If I recall correctly, we agreed that the latter is the behavior we
wanted (because it is simpler for users, matches the fact that "-cpu"
already affects multiple CPU devices [it already affects all the CPUs
created on startup], and is the most common use-case [creating CPUs that
look basically the same]).

-- 
Eduardo