linux-kernel - Re: udev kset_create_and_add() with own struct kobj

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Message-ID: <2024071509-closable-drop-down-3a7f@gregkh>
Date: Mon, 15 Jul 2024 17:33:32 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Alexander Aring <aahringo@...hat.com>
Cc: rafael@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	gfs2 <gfs2@...ts.linux.dev>, David Teigland <teigland@...hat.com>
Subject: Re: udev kset_create_and_add() with own struct kobj_type?

On Mon, Jul 15, 2024 at 11:27:00AM -0400, Alexander Aring wrote:
> Hi,
> 
> I am currently implementing namespace support into the fs/dlm
> subsystem. The DLM subsystem uses kset_create_and_add("dlm",
> &dlm_uevent_ops, kernel_kobj); to create the "dlm" sysfs directory.
> Underneath it creates for each lockspace a subdirectory using
> kobject_init_and_add() with a non-static name and being known during
> runtime.
> 
> Now I want to add namespace support and need to change the "default"
> kset->kobj.ktype = &kset_ktype; that is set by
> kset_create_and_add()->kset_create() to my own kobj_type because I
> need to implement a different ".child_ns_type" callback before
> kset_register() is called.
> 
> So kset_create_and_add() does not allow me to add my own
> ".child_ns_type" callback for the kset that is required for me to have
> my sysfs "kernel/dlm" directory separated by each net-namespace
> without breaking any backwards compatibility.

I don't understand, what "backwards compatibility" is happening here?

> My current solution is that I mostly copy&pasted the code of
> kset_create_and_add()/kset_create() to have a way to tell my own
> struct kobj_type that contains the implemented my own ".child_ns_type"
> callback.

Ick.

> I am writing this mail to get some advice on what I can do here
> without doing the copy&pasted code?
> Add a parameter to kset_create_and_add() that allows me to set an
> "struct kobj_type"?
> Introducing a new function that does allow me to set the new parameter
> (I probably like that because then I don't need to update all other
> users)?

A new function would be ok, but I hate it how filesystems have to use
"raw" kobjects and the like all the time.  It's rough, sorry.

Also, I didn't think sysfs namespaces worked for anything except
networking stuff.  Are you sure you really need this?  Where is your
"namespace" defined at?

thanks,

greg k-h