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

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Date:   Mon, 29 Nov 2021 13:01:26 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
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 Thu, Nov 25, 2021 at 05:14:23PM +0100, Petr Mladek wrote:
> 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?

Yes because it is __init and we allow / guide folks to *think* clearly
about not stopping the init process when it comes to sysctls on failure.

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

We can open code those.

> 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.

For most case I have seen so far special casing init seems like a worthy
objective. When we're done with the full conversion we can re-visit
things but at this point I can't say sharing this outside of init uses
makes too much sense.

  Luis