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

Hi Breno and Andreas,

I'm in favor of this RFC as I think the current flow of needing to
create the cmdline0 dir in the netconsole configfs (when DYNAMIC config
is enabled) prior to modifying the values is not ideal.

I think there are good points shared about sysfs vs. configfs being used
for the cmdline target modification and wanted to add my thoughts.

On Fri, Dec 05, 2025 at 08:29:04PM +0100, Andreas Hindborg wrote:

"Breno Leitao" [off-list ref] writes:

quoted

Hello Andreas,

On Fri, Dec 05, 2025 at 06:35:12PM +0100, Andreas Hindborg wrote:

quoted

"Breno Leitao" [off-list ref] writes:

quoted

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.

quoted

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.

Although technically feasible, this approach leads to an inconsistent
and confusing management of the netconsole targets. A configfs path for
user-space created targets and a sysfs path for the cmdline initiated
target that can also be modified from userspace (e.g. to update
remote_ip or userdata fields).

I think Breno's approach sets up for the most intuitive user experience.
The cmdline config for netconsole is also user-provided, so it seems
like it should behave as a pre-populated configfs target that happens to
pass from cmdline through netconsole module init to the current configfs
interface. The initial values are not determined by the kernel itself.

Best regards,
Andreas Hindborg