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 12:27:43 +0200
From:   Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, borntraeger@...ibm.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] KVM: trigger uevents when starting or stopping a
 VM

On Tue, 4 Jul 2017 11:23:36 +0200
Paolo Bonzini <pbonzini@...hat.com> 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.
> 
> 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).

I'll add those

> 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;
> >   
>