linux-kernel - Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg

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Date:   Tue, 5 May 2020 19:50:59 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        James Morris <jmorris@...ei.org>,
        Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>, anton@...msg.org,
        ccross@...roid.com, Tony Luck <tony.luck@...el.com>,
        robh+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg_dumper

On (20/05/05 00:21), Pavel Tatashin wrote:
> > > I changed it to make code cleaner:  for such basic operation there are
> > > too many conditions if we will keep it inside the kmsg_dump().
> > > However, if being able to set always_kmsg_dump dynamically during
> > > runtime is deemed important, I can change it back to be checked in
> > > kmsg_dump.
> >
> > If you agree that we do not have to modify this variable dynamically,
> > I will also change the permission here:
> > module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
> 
> Hi Sergey,

Hi Pavel,

> After thinking about this. I will move this logic back to kmsg_dump(),
> to keep the current behavior where kmsg_dump can be modified during
> runtime.

Agreed. I think that sysfs knobs and user-visible API need to preserve
their behaviour. There is a deprecation protocol, but usually it takes
many years of WARN_ON() and pr_err("this knob will be removed") before
we can change anything. E.g. sysctl has been deprecated for about a
decade IIRC before it was actually removed.

	-ss