linux-kernel - Re: [PATCH v3 19/30] liveupdate: luo

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Message-ID: <2025100953-plug-acting-9530@gregkh>
Date: Thu, 9 Oct 2025 07:20:35 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: "yanjun.zhu" <yanjun.zhu@...ux.dev>
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Subject: Re: [PATCH v3 19/30] liveupdate: luo_sysfs: add sysfs state
 monitoring

On Wed, Oct 08, 2025 at 06:07:00PM -0700, yanjun.zhu wrote:
> > +#define LUO_DIR_NAME	"liveupdate"
> > +
> > +void luo_sysfs_notify(void)
> > +{
> > +	if (luo_sysfs_initialized)
> > +		sysfs_notify(kernel_kobj, LUO_DIR_NAME, "state");
> > +}
> > +
> > +/* Show the current live update state */
> > +static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
> > +			  char *buf)
> > +{
> > +	return sysfs_emit(buf, "%s\n", luo_current_state_str());
> 
> Because the window of kernel live update is short, it is difficult to
> statistics how many times the kernel is live updated.
> 
> Is it possible to add a variable to statistics the times that the kernel is
> live updated?
> 
> For example, define a global variable of type atomic_t or u64 in the core
> module:
> 
> #include <linux/atomic.h>
> 
> static atomic_t klu_counter = ATOMIC_INIT(0);
> 
> 
> Every time a live update completes successfully, increment the counter:
> 
> atomic_inc(&klu_counter);
> 
> Then exporting this value through /proc or /sys so that user space can check
> it:
> 
> static ssize_t klu_counter_show(struct kobject *kobj, struct kobj_attribute
> *attr, char *buf)
> {
>     return sprintf(buf, "%d\n", atomic_read(&klu_counter));
> }

But the value can change right after you read it, so how do you "know"
it is up to date?

What exactly do you want to do with this type of information?  What are
you going to do with that information?

thanks,

greg k-h