From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7ED3A190676; Wed, 30 Apr 2025 16:58:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746032330; cv=none; b=clhBcH60POzKkdgmq2/Qf83yuqroZh2hW98HYCkZ8EwFeD5nLIetHlI3IYORkEhSj5u5eHkx8qt+w8vLtKLPUMdQ6eEaSMrfRO2+fSeVSPqZ7LOLHGlPb9SQXC4KqUKhradz21S5I9X72szrJG1zTn3WCchxszLS7e8cSltmq94= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746032330; c=relaxed/simple; bh=KbNoo8IuXKgkWpm6XiUqHyCkzgi2Y5PoLRe84tOlwAA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Y3G5ermMFpvkDD7XlD03oWgL2LqWUG2Cg33S0oJecVdCHXPh5NdTaIxe4gCjwYiRfAMiZA47I8ZDTLnbE7tt8czWavnPmNpx3zmDADWO9HfO0lWBkDx0NzC0c/UxnOFkZ0e9MBLvH6pTIzH+XDeZcvTq2q43ALrHjkdaJ6NEs1M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gJgSmQL3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="gJgSmQL3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 53919C4CEE7; Wed, 30 Apr 2025 16:58:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1746032330; bh=KbNoo8IuXKgkWpm6XiUqHyCkzgi2Y5PoLRe84tOlwAA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gJgSmQL3PEHgOBv+tqynMPpReBjxDR0nmy13htO/qBvlNxrN/P9XDsgHlCq4KBh40 P+3WASGL14uiwG0OTNmFe3nomkOdnbLszeW6m5Hkl4QCV0raTp1ceq5D1Vn95gkJNR vbLiD66gtJu21icCwQd52v2ZjDoOkjeGRj+iz+dc= Date: Wed, 30 Apr 2025 18:58:46 +0200 From: Greg Kroah-Hartman To: Matthew Maurer Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , "Rafael J. Wysocki" , Sami Tolvanen , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH 1/8] rust: debugfs: Bind DebugFS directory creation Message-ID: <2025043059-unlined-plausible-644e@gregkh> References: <20250429-debugfs-rust-v1-0-6b6e7cb7929f@google.com> <20250429-debugfs-rust-v1-1-6b6e7cb7929f@google.com> <2025043021-plaza-grip-2916@gregkh> <2025043022-travesty-slicing-2089@gregkh> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Apr 30, 2025 at 08:31:29AM -0700, Matthew Maurer wrote: > On Wed, Apr 30, 2025 at 8:23 AM Greg Kroah-Hartman > wrote: > > > > On Wed, Apr 30, 2025 at 08:10:44AM -0700, Matthew Maurer wrote: > > > On Wed, Apr 30, 2025 at 5:06 AM Greg Kroah-Hartman > > > wrote: > > > > > > > > On Tue, Apr 29, 2025 at 11:15:55PM +0000, Matthew Maurer wrote: > > > > > The basic API relies on `dput` to prevent leaks. Use of `debugfs_remove` > > > > > is delayed until the more full-featured API, because we need to avoid > > > > > the user having an reference to a dir that is recursively removed. > > > > > > > > > > Signed-off-by: Matthew Maurer > > > > > > > > First off, many thanks for doing this. I like this in general, but I > > > > have loads of specific questions/comments. Don't take that as a > > > > criticism of this feature, I really want these bindings to be in the > > > > tree and work hopefully better/cleaner than the userspace ones do. > > > > > > > > First off, the main "rule" of debugfs is that you should NEVER care > > > > about the return value of any debugfs function. So much so that the C > > > > side hides errors almost entirely where possible. I'd like to see this > > > > carried through to the Rust side as well, but I think you didn't do that > > > > for various "traditional" reasons. > > > > > > Sure, I mostly had to do error checking because I was using an > > > `ARef` to represent a directory, which meant that the underlying > > > directory needed to be a valid pointer. Given that you've said that > > > the returned `dentry *` should never be used as an actual `dentry`, > > > only as an abstract handle to a DebugFS object, that requirement goes > > > away, and I can remove the error handling code and always successfully > > > return a `Dir`, even in cases where an error has occurred. > > > > Great! > > > > Except when debugfs is not enabled, then what are you going to return? > > The same structure, or an error? > > > > I'd vote for the same pointer to the structure, just to make it more > > obvious that this is a totally opaque thing and that no caller should > > ever know or care if debugfs is working or even present in the system. > > > > Note that some drivers will want to save a bit of space if debugfs is > > not enabled in the build, so be prepared to make the binding work > > somehow that way too. Can you have an "empty" object that takes no > > memory? Or is this too overthinking things? > > Based on what you've expressed, I think what makes sense is: > > * Initial patch will always return the same `Dir`, just sometimes it > will be a wrapper around a pointer that is an error code, and > sometimes it will be a useful `dentry` pointer. This will match the > current behavior of C code to my understanding. Great. > * Follow-up (probably still in this series) will check > `CONFIG_DEBUG_FS`, and if it's off, will just make `Dir` into a ZST, > and just discard the pointer. This would be an improvement upon the C > interface, because drivers would get the shrinkage without needing to > add conditionals on `CONFIG_DEBUG_FS` in their own driver. You're going to have to check CONFIG_DEBUG_FS anyway for this series, otherwise things aren't going to build properly, so this sounds like a great way to handle that. thanks, greg k-h