linux-kernel - Re: [PATCH v2 1/9] sysctl: add a new register_sysctl

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Date:   Thu, 25 Nov 2021 17:14:23 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     akpm@...ux-foundation.org, keescook@...omium.org,
        yzaikin@...gle.com, nixiaoming@...wei.com, ebiederm@...ssion.com,
        peterz@...radead.org, gregkh@...uxfoundation.org, pjt@...gle.com,
        liu.hailong6@....com.cn, andriy.shevchenko@...ux.intel.com,
        sre@...nel.org, penguin-kernel@...ove.sakura.ne.jp,
        senozhatsky@...omium.org, wangqing@...o.com, bcrl@...ck.org,
        viro@...iv.linux.org.uk, jack@...e.cz, amir73il@...il.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/9] sysctl: add a new register_sysctl_init() interface

On Tue 2021-11-23 12:23:39, Luis Chamberlain wrote:
> From: Xiaoming Ni <nixiaoming@...wei.com>
> 
> The kernel/sysctl.c is a kitchen sink where everyone leaves
> their dirty dishes, this makes it very difficult to maintain.
> 
> To help with this maintenance let's start by moving sysctls to
> places where they actually belong. The proc sysctl maintainers
> do not want to know what sysctl knobs you wish to add for your own
> piece of code, we just care about the core logic.
> 
> Today though folks heavily rely on tables on kernel/sysctl.c so
> they can easily just extend this table with their needed sysctls.
> In order to help users move their sysctls out we need to provide a
> helper which can be used during code initialization.
> 
> We special-case the initialization use of register_sysctl() since
> it *is* safe to fail, given all that sysctls do is provide a dynamic
> interface to query or modify at runtime an existing variable. So the
> use case of register_sysctl() on init should *not* stop if the sysctls
> don't end up getting registered. It would be counter productive to
> stop boot if a simple sysctl registration failed.
>
> Provide a helper for init then, and document the recommended init
> levels to use for callers of this routine. We will later use this
> in subsequent patches to start slimming down kernel/sysctl.c tables
> and moving sysctl registration to the code which actually needs
> these sysctls.

Do we really need a new helper for this?
Is the failure acceptable only during system initialization?

The warning would be useful even for the original register_sysctl().

It should be up-to-the caller to decide if the failure is fatal
or not. It might be enough to document the reasoning why a warning
is enough in most cases.

Best Regards,
Petr