linux-kernel - register_device: was: Re: [PATCH v6 06/11] printk: console: Introduce sysfs interface for per-console loglevels

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Message-ID: <ZzTM04qQXOg2RsOa@pathway.suse.cz>
Date: Wed, 13 Nov 2024 16:59:15 +0100
From: Petr Mladek <pmladek@...e.com>
To: Chris Down <chris@...isdown.name>
Cc: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Tony Lindgren <tony.lindgren@...ux.intel.com>, kernel-team@...com
Subject: register_device: was: Re: [PATCH v6 06/11] printk: console:
 Introduce sysfs interface for per-console loglevels

> A sysfs interface under /sys/class/console/ is created that permits
> viewing and configuring per-console attributes. This is the main
> interface with which we expect users to interact with and configure
> per-console loglevels.

> diff --git a/kernel/printk/sysfs.c b/kernel/printk/sysfs.c
> new file mode 100644
> index 000000000000..e24590074861
> --- /dev/null
> +++ b/kernel/printk/sysfs.c
> +ATTRIBUTE_GROUPS(console_sysfs);
> +
> +static void console_classdev_release(struct device *dev)
> +{
> +	kfree(dev);
> +}
> +
> +void console_register_device(struct console *con)
> +{
> +	/*
> +	 * We might be called from register_console() before the class is
> +	 * registered. If that happens, we'll take care of it in
> +	 * printk_late_init.
> +	 */
> +	if (IS_ERR_OR_NULL(console_class))
> +		return;
> +
> +	if (WARN_ON(con->classdev))
> +		return;
> +
> +	con->classdev = kzalloc(sizeof(struct device), GFP_KERNEL);
> +	if (!con->classdev)
> +		return;
> +
> +	device_initialize(con->classdev);
> +	dev_set_name(con->classdev, "%s%d", con->name, con->index);
> +	dev_set_drvdata(con->classdev, con);
> +	con->classdev->release = console_classdev_release;
> +	con->classdev->class = console_class;
> +	if (device_add(con->classdev))
> +		put_device(con->classdev);

Honestly, I am not sure how to review this. I am not familiar with
these APIs. I have spent few hours trying to investigate various
drivers but I did not find any similar use case. I tried to look
for documentation but I did not find any good HOWTO.

It seems to work but it is the only thing that I could
say about it ;-)

Just by chance, do you have any pointers into a code or
documentation which could help me to feel more comfortable?

> +}
> +

Best Regards,
Petr