Re: [PATCH v2 1/1] KVM: trigger uevents when starting or stopping a VM

[Paolo Bonzini]

On 06/07/2017 12:48, 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 four environment variables:
> 
> KVM_VM_CREATED indicates how many times a new VM has been created. It
>                is useful for example to trigger specific actions when
>                the first VM is started
> KVM_VM_COUNT indicates how many VMs are currently active. This can be
>              used for logging or monitoring purposes
> KVM_VM_PID has the pid of the KVM process that has been started or
>            stopped. This can be used to perform process-specific
>            tuning.
> KVM_VM_STATS_PATH contains the path in /sys to the directory with all
>                   the runtime statistics for this VM. This is useful
>                   for performance monitoring and profiling.
> 
> Specific udev rules can be then set up in userspace to deal with the
> creation or destruction of VMs as needed.

Sorry I have a few more remarks on this---I have now checked other
callers of kobject_uevent_env, and there are couple improvements we can
make.

First, the environment variables names are usually very short.  So I'd
ask you to just name them CREATED, COUNT, PID, STATS_PATH.

Second, there is usually an EVENT variable which, in our case, could be
just one of EVENT=create or EVENT=destroy.

Thanks,

Paolo

> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
> ---
>  virt/kvm/kvm_main.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 6e3b12c..f4cf7d2 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -130,6 +130,12 @@ EXPORT_SYMBOL_GPL(kvm_rebooting);
>  
>  static bool largepages_enabled = true;
>  
> +#define KVM_EVENT_CREATE_VM 0
> +#define KVM_EVENT_DESTROY_VM 1
> +static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm);
> +static unsigned long long kvm_createvm_count;
> +static unsigned long long kvm_active_vms;
> +
>  bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>  {
>  	if (pfn_valid(pfn))
> @@ -740,6 +746,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
>  	int i;
>  	struct mm_struct *mm = kvm->mm;
>  
> +	kvm_uevent_notify_change(KVM_EVENT_DESTROY_VM, kvm);
>  	kvm_destroy_vm_debugfs(kvm);
>  	kvm_arch_sync_events(kvm);
>  	spin_lock(&kvm_lock);
> @@ -3212,6 +3219,7 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
>  		fput(file);
>  		return -ENOMEM;
>  	}
> +	kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm);
>  
>  	fd_install(r, file);
>  	return r;
> @@ -3864,6 +3872,48 @@ static const struct file_operations *stat_fops[] = {
>  	[KVM_STAT_VM]   = &vm_stat_fops,
>  };
>  
> +static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
> +{
> +	char cbuf[40], abuf[40], pidbuf[40], pathvar[18] = "KVM_VM_STATS_PATH=";
> +	char *ptr[5] = {cbuf, abuf, pidbuf, NULL, NULL};
> +	char *tmp, *pathbuf;
> +	unsigned long long created, active;
> +
> +	if (!kvm_dev.this_device || !kvm || !kvm->debugfs_dentry)
> +		return;
> +
> +	spin_lock(&kvm_lock);
> +	if (type == KVM_EVENT_CREATE_VM) {
> +		kvm_createvm_count++;
> +		kvm_active_vms++;
> +	} else if (type == KVM_EVENT_DESTROY_VM) {
> +		kvm_active_vms--;
> +	}
> +	created = kvm_createvm_count;
> +	active = kvm_active_vms;
> +	spin_unlock(&kvm_lock);
> +
> +	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
> +	if (pathbuf) {
> +		tmp = dentry_path_raw(kvm->debugfs_dentry,
> +				      pathbuf + sizeof(pathvar),
> +				      PATH_MAX - sizeof(pathvar));
> +		if (!IS_ERR(tmp)) {
> +			memcpy(tmp - sizeof(pathvar), pathvar, sizeof(pathvar));
> +			ptr[3] = tmp - sizeof(pathvar);
> +		}
> +	}
> +	snprintf(cbuf, sizeof(cbuf), "KVM_VM_CREATED=%llu", created);
> +	snprintf(abuf, sizeof(abuf), "KVM_VM_ACTIVE=%llu", active);
> +	snprintf(pidbuf, sizeof(pidbuf), "KVM_VM_PID=%s",
> +		 kvm->debugfs_dentry->d_name.name);
> +	tmp = strchr(pidbuf, '-');
> +	if (tmp)
> +		*tmp = '\0';
> +	kobject_uevent_env(&kvm_dev.this_device->kobj, KOBJ_CHANGE, ptr);
> +	kfree(pathbuf);
> +}
> +
>  static int kvm_init_debug(void)
>  {
>  	int r = -EEXIST;
>