Subject: Re: [PATCH v1 1/1] KVM: trigger uevents when starting or stopping a
 VM
To: Paolo Bonzini <pbonzini@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>, kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
References: <1499159018-19782-1-git-send-email-imbrenda@linux.vnet.ibm.com>
 <8d239a6c-3625-6964-7fd2-b753f2e15bf5@redhat.com>
From: Christian Borntraeger <borntraeger@de.ibm.com>
Date: Tue, 4 Jul 2017 11:25:26 +0200
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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.


> 
> 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@linux.vnet.ibm.com>
>> ---
>>  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;
>>
>