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 158FB1B4122; Fri, 6 Dec 2024 08:55:33 +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=1733475335; cv=none; b=pZjgCTcDlDTpr0qE/fIW36HI3ByakIS2pEJJdFKnCiQsXaRiWG6ptfqnCxtGNI3uMnrMjcTyA0sfM/L3PGbjn5uY9RjOqafyGDd9tDI9aMVfbRHJL6SbBMWaszhv8SJsH5YgaN6O2M0l1zDk6Q8UxARbUgWVq1igVtrXdCeFWIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733475335; c=relaxed/simple; bh=L6yN7mD5rKVPN+tUKvRk9yYl6zI+0cfg0Z1YEPW68Ys=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CReMah4i+VtaL37FOSJm1v1sAdvTCZhU/HhvwwWkx/En4qyf1x9waynpVLZdnBRWvwuYZ6SHZ7Xuk6PRRdboRAcW+8WASLE3Lg9Wl+fDO18661jIfE+Q0g2ZoNBzO22rwqXTUELvD1mfGss2ajVl1+RT627Tevv7efGwk7mRfqQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=2UuGPlh5; 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="2UuGPlh5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE7C2C4CED1; Fri, 6 Dec 2024 08:55:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1733475333; bh=L6yN7mD5rKVPN+tUKvRk9yYl6zI+0cfg0Z1YEPW68Ys=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=2UuGPlh5lVMkaJBzRw92Ro+VgeHLMjpc0xzpHzY4GGFBtTFgfbdUkTOaATmlUihTx CSKYse/KRWJUv/5C3hYmoZo/SzUU1fdy2iB/huG9QvHhr+oshcYkDrmeTZVkOEFrKw yhUj26SuCe39/PVN4g9mu/lv8jz9WT5OOm/tZGKA= Date: Fri, 6 Dec 2024 09:55:29 +0100 From: Greg KH To: Alice Ryhl Cc: Lee Jones , linux-kernel@vger.kernel.org, arnd@arndb.de, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@kernel.org, tmgross@umich.edu, rust-for-linux@vger.kernel.org Subject: Re: [PATCH v3 0/5] rust: miscdevice: Provide sample driver using the new MiscDevice bindings Message-ID: <2024120609-stamina-slit-5a84@gregkh> References: <20241205162531.1883859-1-lee@kernel.org> <2024120632-hardwired-hardhead-1906@gregkh> <20241206074443.GJ8882@google.com> <2024120622-unvalued-wriggle-7942@gregkh> <2024120615-concert-oven-66f1@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@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 Fri, Dec 06, 2024 at 09:51:55AM +0100, Alice Ryhl wrote: > On Fri, Dec 6, 2024 at 9:44 AM Greg KH wrote: > > > > On Fri, Dec 06, 2024 at 09:31:28AM +0100, Alice Ryhl wrote: > > > On Fri, Dec 6, 2024 at 9:11 AM Greg KH wrote: > > > > > > > > On Fri, Dec 06, 2024 at 07:44:43AM +0000, Lee Jones wrote: > > > > > On Fri, 06 Dec 2024, Greg KH wrote: > > > > > > > > > > > On Thu, Dec 05, 2024 at 04:25:17PM +0000, Lee Jones wrote: > > > > > > > It has been suggested that the driver should use dev_info() instead of > > > > > > > pr_info() however there is currently no scaffolding to successfully pull > > > > > > > a 'struct device' out from driver data post register(). This is being > > > > > > > worked on and we will convert this over in due course. > > > > > > > > > > > > But the miscdevice.rs change provides this to you, right? Or if not, > > > > > > why not? > > > > > > > > > > This does allow us to pull the 'struct device *` out from `struct > > > > > miscdevice`; however, since this resides in MiscDeviceRegistration, > > > > > which we lose access to after .init, we have no means to call it. > > > > > > > > > > Alice is going to work on a way to use ThisModule to get the > > > > > MiscDeviceRegistration reference back from anywhere in the module. Until > > > > > that piece lands, we can't call MiscDeviceRegistration::device() outside > > > > > of RustMiscDeviceModule. > > > > > > > > That seems crazy, as ThisModule shouldn't be dealing with a static misc > > > > device, what happens for dynamically created ones like all > > > > normal/sane/non-example drivers do? This should "just" be a dynamic > > > > object that is NOT tied to the module object, or worst case, a "static" > > > > structure that is tied to the module I guess? > > > > > > > > Anyway, I'll let you all work it out, good luck! > > > > > > If you store it somewhere else, you're probably okay. The current > > > place is just hard to access. > > > > > > The problem is that the Rust module abstractions generate a global > > > variable that holds an RustMiscDeviceModule which is initialized in > > > init_module() and destroyed in cleanup_module(). To have safe access > > > to this global, we need to ensure that you access it only between > > > init_module() and cleanup_module(). For loadable modules, the > > > try_module_get() logic seems perfect, so in Miscdevice::open we have a > > > file pointer, which implies that the fs infrastructure took a refcount > > > on fops->owner, which it can only do once init_module() is done. > > > > > > Unfortunately, this doesn't translate to built-in modules since the > > > owner pointer is just null, and try_module_get performs no checks at > > > all. > > > > > > Also, I'm realizing now that try_module_get() succeeds even if `state > > > == MODULE_STATE_COMING`. :( > > > > > > So in conclusion, I don't know of any way to provide safe access to > > > the global RustMiscDeviceModule value. > > > > Odd. How is this any different than what is going to happen for > > platform or other drivers of any other type? Sometimes they want to > > only create one single "static" object and register it with the bus they > > are assigned to. > > > > Do we need to have a RuscMiscDevice object somewhere instead that > > doesn't care about the module logic at all? And then just use a > > "normal" rust module object to create a single instance of that which > > the misc binding will handle? > > Actually, I guess we can access the miscdevice in open via the pointer > that misc_open() stashes into the file private data. We don't have to > go through the global variable. Ah, nice, that's how a "normal" misc device should be doing this, so yes, that sounds good! thanks, greg k-h