linux-kernel - Re: [PATCH v2] netconsole: Append kernel version to message

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Date:   Fri, 14 Jul 2023 13:41:55 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Breno Leitao <leitao@...ian.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>, sergey.senozhatsky@...il.com,
        tj@...nel.org, stephen@...workplumber.org,
        Dave Jones <davej@...emonkey.org.uk>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] netconsole: Append kernel version to message

On Fri 2023-07-07 06:29:11, Breno Leitao wrote:
> Create a new netconsole runtime option that prepends the kernel version in
> the netconsole message. This is useful to map kernel messages to kernel
> version in a simple way, i.e., without checking somewhere which kernel
> version the host that sent the message is using.
> 
> If this option is selected, then the "<release>," is prepended before the
> netconsole message. This is an example of a netconsole output, with
> release feature enabled:
> 
> 	6.4.0-01762-ga1ba2ffe946e;12,426,112883998,-;this is a test
> 
> Calvin Owens send a RFC about this problem in 2016[1], but his
> approach was a bit more intrusive, changing the printk subsystem. This
> approach is lighter, and just append the information in the last mile,
> just before netconsole push the message to netpoll.

Thanks a lot for solving this on the netconsole level. The extended
console format is used also for /dev/kmsg. Which is then used by
systemd journal, dmesg, and maybe other userspace tools. Any format
changes might break these tools.

I have glanced over the patch and have two comments.


> @@ -254,6 +267,11 @@ static ssize_t extended_show(struct config_item *item, char *buf)
>  	return snprintf(buf, PAGE_SIZE, "%d\n", to_target(item)->extended);
>  }
>  
> +static ssize_t release_show(struct config_item *item, char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE, "%d\n", to_target(item)->release);

I have learned recently that sysfs_emit() was preferred over snprintf() in the
_show() callbacks.

> +}
> +
>  static ssize_t dev_name_show(struct config_item *item, char *buf)
>  {
>  	return snprintf(buf, PAGE_SIZE, "%s\n", to_target(item)->np.dev_name);
> @@ -366,6 +389,38 @@ static ssize_t enabled_store(struct config_item *item,
>  	return err;
>  }
>  
> +static ssize_t release_store(struct config_item *item, const char *buf,
> +			     size_t count)
> +{
> +	struct netconsole_target *nt = to_target(item);
> +	int release;
> +	int err;
> +
> +	mutex_lock(&dynamic_netconsole_mutex);
> +	if (nt->enabled) {
> +		pr_err("target (%s) is enabled, disable to update parameters\n",
> +		       config_item_name(&nt->item));
> +		err = -EINVAL;
> +		goto out_unlock;
> +	}
> +
> +	err = kstrtoint(buf, 10, &release);
> +	if (err < 0)
> +		goto out_unlock;
> +	if (release < 0 || release > 1) {
> +		err = -EINVAL;
> +		goto out_unlock;
> +	}

You might consider using:

	bool enabled;

	err = kstrtobool(buf, &enabled);
	if (err)
		goto unlock;


It accepts more input values, for example, 1/0, y/n, Y/N, ...

Well, I see that kstrtoint() is used also in enabled_store().
It might be confusing when "/enabled" supports only "1/0"
and "/release" supports more variants.

> +
> +	nt->release = release;
> +
> +	mutex_unlock(&dynamic_netconsole_mutex);
> +	return strnlen(buf, count);
> +out_unlock:
> +	mutex_unlock(&dynamic_netconsole_mutex);
> +	return err;
> +}
> +

Best Regards,
Petr