linux-kernel - Re: [PATCH 4/4] printk: Add a device attribute for the per-console loglevel

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Message-ID: <20190304191006.GA51516@calvinowens-mba.dhcp.thefacebook.com>
Date:   Mon, 4 Mar 2019 19:10:14 +0000
From:   Calvin Owens <calvinowens@...com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
CC:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH 4/4] printk: Add a device attribute for the per-console
 loglevel

On Monday 03/04 at 17:06 +0900, Sergey Senozhatsky wrote:
> On (03/01/19 16:48), Calvin Owens wrote:
> > +static struct attribute *console_sysfs_attrs[] = {
> > +	&dev_attr_loglevel.attr,
> > +	NULL,
> > +};
> > +ATTRIBUTE_GROUPS(console_sysfs);
> > +
> >  static struct bus_type console_subsys = {
> >  	.name = "console",
> > +	.dev_groups = console_sysfs_groups,
> >  };
> 
> Do we really need to change this dynamically? Console options are
> traditionally static (boot param or DT). Can we also be happy with
> the static per-console loglevel?

It really does need to be runtime configurable: there are a lot of usecases
that enables, like turning the fast console up to KERN_DEBUG on a pile of
machines you want to take a closer look at. The 'kernel.printk' global
loglevel is also already changable at runtime, and since that setting
interacts with this one it would be strange if only the former were able
to be changed.

I also want to add more attribute knobs related to extended consoles,
so the plumbing to get things exposed in sysfs is worth it for me.

Thanks,
Calvin