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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 <thuth@redhat.com>
Message-Id: <20200123170256.12386-1-thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
This commit is contained in:
Thomas Huth 2020-01-23 18:02:56 +01:00 committed by Cornelia Huck
parent a2fb6b000c
commit 3e0209bbd6
1 changed files with 13 additions and 3 deletions
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16
hw/s390x/s390-virtio-ccw.c
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@ -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;
}