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 119BD1BD9E4; Fri, 6 Dec 2024 09:59:03 +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=1733479143; cv=none; b=JfbAUeo1XX6TLvbNlAih7X2cNKUb1A8jku0sJ01Qd3XdTjA6QcrVvvQ4La/C9EEgOCygsNkUZPbl+ri6rE8hkcHzMczUuo8FPsQSPpNOIapiirumi8JQn1U+FgoKcGetcNurCIWtJEOqyDl7hBncQLThHxAtOgHsfjiDy+Hcx7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733479143; c=relaxed/simple; bh=Rf20ZeLVZbNe3/ItJRnSQAA0M7/5CB4BpvbXhbNuXBM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Sq53TF42h5zWycTTrwFn4GQApvKBqk4ceEGbPCtvxHaHxAX2KvvFhnPBMid/CqNTo9W4F0+bS/lfOwSqJ+EUdT098/mzbehc8R7agvUaz09DzkG65mzii3aORZus8XtcPSHOGW093oXp+DdtPOeETNXibi5/mOEDlXhPAdpTPMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Uo3fcH9c; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Uo3fcH9c" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A30DC4CED1; Fri, 6 Dec 2024 09:58:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1733479142; bh=Rf20ZeLVZbNe3/ItJRnSQAA0M7/5CB4BpvbXhbNuXBM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Uo3fcH9cRwF83aocJNJgtUEFKMnWzmgEquCJC62QmvAOsBo1215g4beR69M2bgrL7 CT0DCy+Rh0rq6il0dMnZfiZYgnpZhE36gMSjlxxRyVGjtflzK++QfDdv3tuZK5w2HP 0P6jzZD/+Q/ewsK/ojCjF6knIsVTsWa7txTSYbE+C86hcv7p7Ioxi/D80zoGeGaOU/ vBXUap/DMUwmzsJ/ffKkhWvFpocMGul6BAJfzNHrOSqKw03n0ZCqistXv5KU1sKpKZ 4pSwA7C4fid0o4MdCFfZqQNS4KD26WMYNJVhhemDd6m6KHZH6i1I/JnahVN/O1egB4 SOA7yifHAIcuQ== Date: Fri, 6 Dec 2024 10:58:57 +0100 From: Danilo Krummrich To: Alice Ryhl Cc: Lee Jones , linux-kernel@vger.kernel.org, arnd@arndb.de, gregkh@linuxfoundation.org, 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 v4 2/4] samples: rust: Provide example using the new Rust MiscDevice abstraction Message-ID: References: <20241206090515.752267-1-lee@kernel.org> <20241206090515.752267-5-lee@kernel.org> 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 10:40:23AM +0100, Alice Ryhl wrote: > On Fri, Dec 6, 2024 at 10:29 AM Danilo Krummrich wrote: > > > > On Fri, Dec 06, 2024 at 09:05:06AM +0000, Lee Jones wrote: > > > This sample driver demonstrates the following basic operations: > > > > > > * Register a Misc Device > > > * Create /dev/rust-misc-device > > > * Provide open call-back for the aforementioned character device > > > * Operate on the character device via a simple ioctl() > > > * Provide close call-back for the character device > > > > > > Signed-off-by: Lee Jones > > > --- > > > samples/rust/Kconfig | 10 ++++ > > > samples/rust/Makefile | 1 + > > > samples/rust/rust_misc_device.rs | 80 ++++++++++++++++++++++++++++++++ > > > 3 files changed, 91 insertions(+) > > > create mode 100644 samples/rust/rust_misc_device.rs > > > > > > diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig > > > index b0f74a81c8f9..df384e679901 100644 > > > --- a/samples/rust/Kconfig > > > +++ b/samples/rust/Kconfig > > > @@ -20,6 +20,16 @@ config SAMPLE_RUST_MINIMAL > > > > > > If unsure, say N. > > > > > > +config SAMPLE_RUST_MISC_DEVICE > > > + tristate "Misc device" > > > + help > > > + This option builds the Rust misc device. > > > + > > > + To compile this as a module, choose M here: > > > + the module will be called rust_misc_device. > > > + > > > + If unsure, say N. > > > + > > > config SAMPLE_RUST_PRINT > > > tristate "Printing macros" > > > help > > > diff --git a/samples/rust/Makefile b/samples/rust/Makefile > > > index c1a5c1655395..ad4b97a98580 100644 > > > --- a/samples/rust/Makefile > > > +++ b/samples/rust/Makefile > > > @@ -2,6 +2,7 @@ > > > ccflags-y += -I$(src) # needed for trace events > > > > > > obj-$(CONFIG_SAMPLE_RUST_MINIMAL) += rust_minimal.o > > > +obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE) += rust_misc_device.o > > > obj-$(CONFIG_SAMPLE_RUST_PRINT) += rust_print.o > > > > > > rust_print-y := rust_print_main.o rust_print_events.o > > > diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs > > > new file mode 100644 > > > index 000000000000..3837532d259e > > > --- /dev/null > > > +++ b/samples/rust/rust_misc_device.rs > > > @@ -0,0 +1,80 @@ > > > +// SPDX-License-Identifier: GPL-2.0 > > > + > > > +// Copyright (C) 2024 Google LLC. > > > + > > > +//! Rust misc device sample. > > > + > > > +use kernel::{ > > > + c_str, > > > + ioctl::_IO, > > > + miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration}, > > > + prelude::*, > > > +}; > > > + > > > +const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 9); > > > + > > > +module! { > > > + type: RustMiscDeviceModule, > > > + name: "rust_misc_device", > > > + author: "Lee Jones", > > > + description: "Rust misc device sample", > > > + license: "GPL", > > > +} > > > + > > > +struct RustMiscDeviceModule { > > > + _miscdev: Pin>>, > > > +} > > > + > > > +impl kernel::Module for RustMiscDeviceModule { > > > + fn init(_module: &'static ThisModule) -> Result { > > > + pr_info!("Initialising Rust Misc Device Sample\n"); > > > + > > > + let options = MiscDeviceOptions { > > > + name: c_str!("rust-misc-device"), > > > + }; > > > + > > > + Ok(Self { > > > + _miscdev: KBox::pin_init( > > > + MiscDeviceRegistration::::register(options), > > > + GFP_KERNEL, > > > + )?, > > > + }) > > > > Since this v4 was sent just when I was commenting on v3: > > > > Why do we add examples where we ask people to allocate those structures with > > kmalloc()? > > > > `MiscDevice` should switch to the generic `Registration` type in [1] and use > > `InPlaceModule`, such that those structures land in the .data section of the > > binary. > > > > [1] https://lore.kernel.org/rust-for-linux/20241205141533.111830-3-dakr@kernel.org/ > > > > > + } > > > +} > > > + > > > +struct RustMiscDevice; > > > + > > > +#[vtable] > > > +impl MiscDevice for RustMiscDevice { > > > + type Ptr = KBox; > > > + > > > + fn open() -> Result> { > > > + pr_info!("Opening Rust Misc Device Sample\n"); > > > > This should be `dev_info!`, but I see why you don't have access to the device > > structure here... > > > > @Greg: How do miscdev drivers do this in C? I looked at a couple of them, but > > all of those seem to use pr_* macros. They can't get the device pointer from > > the inode or file pointer. > > > > However, C drivers could refer to the struct miscdevice directly since it's > > almost always a static variable in the file scope. > > > > In Rust we do the static allocation part with `InPlaceModule` as mentioned > > above. However, this still doesn't let us refer to the underlying struct > > miscdevice. > > > > This all would be much cleaner if there'd be a "fake" probe() callback for a > > struct miscdevice. This way we could perfectly align the miscdevice abstraction > > with the abstractions for all other drivers, such as PCI, platform, etc. > > It turns out that the file private data is a pointer to the `struct > miscdevice` in fops->open(), so we can access it in open. To access it > in other fops hooks, we need to take a refcount on the device in open > and stash it. Even better! I suggest to represent it as `misc::Device` and align it with `platform::Device`, `pci::Device`, etc. > > Alice >