linux-kernel - Re: [PATCH RFC 0/2] configfs: enable kernel-space item registration

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Message-ID: <875xakwwvz.fsf@t14s.mail-host-address-is-not-set>
Date: Fri, 05 Dec 2025 20:29:04 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 linux-kernel@...r.kernel.org, hch@...radead.org, jlbec@...lplan.org,
 linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
 gustavold@...il.com, asantostc@...il.com, calvin@...nvd.org,
 kernel-team@...a.com
Subject: Re: [PATCH RFC 0/2] configfs: enable kernel-space item registration

"Breno Leitao" <leitao@...ian.org> writes:

> Hello Andreas,
>
> On Fri, Dec 05, 2025 at 06:35:12PM +0100, Andreas Hindborg wrote:
>> "Breno Leitao" <leitao@...ian.org> writes:
>>
>> > This series introduces a new kernel-space item registration API for configfs
>> > to enable subsystems to programmatically create configfs items whose lifecycle
>> > is controlled by the kernel rather than userspace.
>> >
>> > Currently, configfs items can only be created via userspace mkdir operations,
>> > which limits their utility for kernel-driven configuration scenarios such as
>> > boot parameters or hardware auto-detection.
>>
>> I thought sysfs would handle this kind of scenarios?
>
> sysfs has gaps as well, to manage user-create items.
>
> Netconsole has two types of "targets". Those created dynamically
> (CONFIG_NETCONSOLE_DYNAMIC), where user can create and remove as many
> targets as it needs, and netconsole would send to it. This fits very
> well in configfs.
>
>   mkdir /sys/kernel/config/netconsole/mytarget
>   .. manage the target using configfs items/files
>   rmdir /sys/kernel/config/netconsole/mytarget
>
> This is a perfect fit for configfs, and I don't see how it would work
> with sysfs.

Right, these go in configfs, we are on the same page about that.

>
> On top of that, there are netconsole targets that are coming from
> cmdline (basically to cover while userspace is not initialized). These
> are coming from cmdline and its life-cycle is managed by the kernel.
> I.e, the kernel knows about them, and wants to expose it to the user
> (which can even disable them later). This is the problem I this patch
> addresses (exposing them easily).

I wonder if these entries could be exposed via sysfs? You could create
the same directory structure as you have in configfs for the user
created devices, so the only thing user space has to do is to point at a
different directory.

Best regards,
Andreas Hindborg