qdev: Don't exit when running into bad -global

qdev: Don't exit when running into bad -global

-global lets you set a nice booby-trap for yourself:

    $ qemu-system-x86_64 -nodefaults -S -display none -usb -monitor stdio -global usb-mouse.usb_version=l
    QEMU 2.1.94 monitor - type 'help' for more information
    (qemu) device_add usb-mouse
    Parameter 'usb_version' expects an int64 value or range
    $ echo $?
    1

Not nice.  Until commit 3196270 we even abort()ed.

The same error triggers if you manage to screw up a machine type's
compat_props.  To demonstrate, change HW_COMPAT_2_1's entry to

            .driver   = "usb-mouse",\
            .property = "usb_version",\
            .value    = "1", \

Then run

    $ qemu-system-x86_64 -usb -M pc-i440fx-2.1 -device usb-mouse
    upstream-qemu: -device usb-mouse: Parameter 'usb_version' expects an int64 value or range
    $ echo $?
    1

One of our creatively cruel error messages.

Since this is actually a coding error, we *should* abort() here.
Replace the error by an assertion failure in this case.

But turn the fatal error into a mere warning when the faulty
GlobalProperty comes from the user.  Looks like this:

    $ qemu-system-x86_64 -nodefaults -S -display none -usb -monitor stdio -global usb-mouse.usb_version=l
    QEMU 2.1.94 monitor - type 'help' for more information
    (qemu) device_add usb-mouse
    Warning: global usb-mouse.usb_version=l ignored (Parameter 'usb_version' expects an int64 value or range)
    (qemu)

This is consistent with how we handle similarly unusable -global in
qdev_prop_check_globals().

You could argue that the error should make device_add fail.  Would be
harder, because we're running within TypeInfo's instance_post_init()
method device_post_init(), which can't fail.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>