linux-kernel - Re: [RFC PATCH 0/6] debugfs: Replace dentry with an opaque handle in debugfs API

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Message-ID: <867c5x3clf.fsf@davidreaver.com>
Date: Mon, 10 Feb 2025 09:59:24 -0800
From: David Reaver <me@...idreaver.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,  "Rafael J . Wysocki"
 <rafael@...nel.org>,  Danilo Krummrich <dakr@...nel.org>,  Christian
 Brauner <brauner@...nel.org>,  Alexander Viro <viro@...iv.linux.org.uk>,
  linux-fsdevel@...r.kernel.org,  cocci@...ia.fr,
  linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/6] debugfs: Replace dentry with an opaque handle
 in debugfs API

Steven Rostedt <rostedt@...dmis.org> writes:

>
> No it will not be fine. You should not be using dentry at all. I thought
> this was going to convert debugfs over to kernfs. The debugfs_node should
> be using kernfs and completely eliminate the use of dentry.
>
> <snip>
>
> What caller should ever touch a dentry? What I got from my "conversation"
> with Linus, is that dentry is an internal caching descriptor of the VFS
> layer, and should only be used by the VFS layer. Nothing outside of VFS
> should ever need a dentry.
>
> -- Steve

I agree that just wrapping a dentry shouldn't be the final state for
debugfs_node, but this patch series is _only_ trying to introduce
debugfs_node as an opaque wrapper/handle.

It isn't clear to me that there is consensus on even using kernfs for
debugfs. Even if there was consensus, a full conversion to kernfs would
take 10x as much code and be extremely difficult to automate. For
example, using kernfs would require migrating all of the debugfs users'
file_operations to use the kernfs equivalent.

I figure any change away from persistent dentry handles for debugfs
requires introducing something akin to debugfs_node, so we could get
that out of the way first.

Thanks,
David Reaver