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

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Date:   Tue, 4 Jul 2017 11:23:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] KVM: trigger uevents when starting or stopping a
 VM



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.

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@...ux.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;
>