From 3e0209bbd6027d60539976b39a8f2131a81e5127 Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Thu, 23 Jan 2020 18:02:56 +0100 Subject: [PATCH] hw/s390x: Add a more verbose comment about get_machine_class() and the wrappers While working on the "Enable adapter interruption suppression again" recently, I had to discover that the meaning of get_machine_class() and the related *_allowed() wrappers is not very obvious. Add a more verbose comment here to clarify how these should be used. Signed-off-by: Thomas Huth Message-Id: <20200123170256.12386-1-thuth@redhat.com> Reviewed-by: David Hildenbrand Signed-off-by: Cornelia Huck --- hw/s390x/s390-virtio-ccw.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c index e0e28139a2..e759eb5f83 100644 --- a/hw/s390x/s390-virtio-ccw.c +++ b/hw/s390x/s390-virtio-ccw.c @@ -505,6 +505,19 @@ static inline void machine_set_dea_key_wrap(Object *obj, bool value, static S390CcwMachineClass *current_mc; +/* + * Get the class of the s390-ccw-virtio machine that is currently in use. + * Note: libvirt is using the "none" machine to probe for the features of the + * host CPU, so in case this is called with the "none" machine, the function + * returns the TYPE_S390_CCW_MACHINE base class. In this base class, all the + * various "*_allowed" variables are enabled, so that the *_allowed() wrappers + * below return the correct default value for the "none" machine. + * + * Attention! Do *not* add additional new wrappers for CPU features (e.g. like + * the ri_allowed() wrapper) via this mechanism anymore. CPU features should + * be handled via the CPU models, i.e. checking with cpu_model_allowed() during + * CPU initialization and s390_has_feat() later should be sufficient. + */ static S390CcwMachineClass *get_machine_class(void) { if (unlikely(!current_mc)) { @@ -521,19 +534,16 @@ static S390CcwMachineClass *get_machine_class(void) bool ri_allowed(void) { - /* for "none" machine this results in true */ return get_machine_class()->ri_allowed; } bool cpu_model_allowed(void) { - /* for "none" machine this results in true */ return get_machine_class()->cpu_model_allowed; } bool hpage_1m_allowed(void) { - /* for "none" machine this results in true */ return get_machine_class()->hpage_1m_allowed; }