Re: [PATCH v1 1/1] KVM: trigger uevents when starting or stopping a VM

[Paolo Bonzini]

On 04/07/2017 11:25, Christian Borntraeger wrote:
> On 07/04/2017 11:23 AM, Paolo Bonzini wrote:
>>
>>
>> On 04/07/2017 11:03, Claudio Imbrenda wrote:
>>> This patch adds a few lines to the KVM common code to fire a
>>> KOBJ_CHANGE uevent whenever a KVM VM is created or destroyed. The event
>>> carries two environment variables:
>>> KVM_VM_CREATED which indicates how many times a new VM has been created,
>>> KVM_VM_COUNT which indicates how many VMs are currently active.
>>
>> I'm not sure why KVM_VM_CREATED is useful, KVM_VM_COUNT can be a bit
>> more interesting though not much.
> 
> I am certainly interested in an trigger from "kvm was never used" to "kvm was used",
> so having something like KVM_VM_CREATED has a value for me.

Fair enough, that's a good use.  Please add it to the commit message,
however.

Paolo

>> But since we are at it, let's also add a PID.  That one is the really
>> useful one, because it gives you something to look at in debugfs.
>> Another possibility is to add the debugfs directory name directly
>> (KVM_VM_STATS_PATH or something like that).
>>
>> Paolo
>>
>>> Specific udev rules can be then set up in userspace to deal with the
>>> creation or destruction of VMs as needed.
>>>
>>> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
>>> ---
>>>  virt/kvm/kvm_main.c | 25 +++++++++++++++++++++++++
>>>  1 file changed, 25 insertions(+)
>>>
>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>> index 6e3b12c..f67aa59 100644
>>> --- a/virt/kvm/kvm_main.c
>>> +++ b/virt/kvm/kvm_main.c
>>> @@ -130,6 +130,10 @@ EXPORT_SYMBOL_GPL(kvm_rebooting);
>>>  
>>>  static bool largepages_enabled = true;
>>>  
>>> +static void kvm_uevent_notify_change(u64 created, u64 active);
>>> +static u64 kvm_createvm_count;
>>> +static u64 kvm_active_vms;
>>> +
>>>  bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>>>  {
>>>  	if (pfn_valid(pfn))
>>> @@ -627,6 +631,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
>>>  {
>>>  	int r, i;
>>>  	struct kvm *kvm = kvm_arch_alloc_vm();
>>> +	u64 activevms, createdvms;
>>>  
>>>  	if (!kvm)
>>>  		return ERR_PTR(-ENOMEM);
>>> @@ -686,9 +691,12 @@ static struct kvm *kvm_create_vm(unsigned long type)
>>>  
>>>  	spin_lock(&kvm_lock);
>>>  	list_add(&kvm->vm_list, &vm_list);
>>> +	createdvms = ++kvm_createvm_count;
>>> +	activevms = ++kvm_active_vms;
>>>  	spin_unlock(&kvm_lock);
>>>  
>>>  	preempt_notifier_inc();
>>> +	kvm_uevent_notify_change(createdvms, activevms);
>>>  
>>>  	return kvm;
>>>  
>>> @@ -739,11 +747,14 @@ static void kvm_destroy_vm(struct kvm *kvm)
>>>  {
>>>  	int i;
>>>  	struct mm_struct *mm = kvm->mm;
>>> +	u64 activevms, createdvms;
>>>  
>>>  	kvm_destroy_vm_debugfs(kvm);
>>>  	kvm_arch_sync_events(kvm);
>>>  	spin_lock(&kvm_lock);
>>>  	list_del(&kvm->vm_list);
>>> +	activevms = --kvm_active_vms;
>>> +	createdvms = kvm_createvm_count;
>>>  	spin_unlock(&kvm_lock);
>>>  	kvm_free_irq_routing(kvm);
>>>  	for (i = 0; i < KVM_NR_BUSES; i++) {
>>> @@ -767,6 +778,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
>>>  	preempt_notifier_dec();
>>>  	hardware_disable_all();
>>>  	mmdrop(mm);
>>> +	kvm_uevent_notify_change(createdvms, activevms);
>>>  }
>>>  
>>>  void kvm_get_kvm(struct kvm *kvm)
>>> @@ -3864,6 +3876,19 @@ static const struct file_operations *stat_fops[] = {
>>>  	[KVM_STAT_VM]   = &vm_stat_fops,
>>>  };
>>>  
>>> +static void kvm_uevent_notify_change(u64 created, u64 active)
>>> +{
>>> +	char createvm_buf[40];
>>> +	char activevm_buf[40];
>>> +	char *ptr[3] = {createvm_buf, activevm_buf, NULL};
>>> +
>>> +	if (!kvm_dev.this_device)
>>> +		return;
>>> +	snprintf(createvm_buf, 40, "KVM_VM_CREATED=%llu", created);
>>> +	snprintf(activevm_buf, 40, "KVM_VM_ACTIVE=%llu", active);
>>> +	kobject_uevent_env(&kvm_dev.this_device->kobj, KOBJ_CHANGE, ptr);
>>> +}
>>> +
>>>  static int kvm_init_debug(void)
>>>  {
>>>  	int r = -EEXIST;
>>>
>>
>