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 99776189520; Mon, 24 Mar 2025 18:13:21 +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=1742840001; cv=none; b=hUJrrYpFU1HTIUcPut2FAm+V7/jP6ygJhltTS3sZmw6h/1U5fEgeaiJD0cHUkWOBjIsGjPrIMI7wBa2vCIl5s3jvt7q/DWY+v578dGzorLTULZQK/zmp+uvbPYqPN3NzdfNuSHKFKBpbnr3BDE9SGxgOR9iRn2lm8vFfCiMGWf0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742840001; c=relaxed/simple; bh=HxL4j75EqQZXg4nUUxuhCgYtvVucbH/8DgVWCMZjacs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e+n+ycl03d+++GEcuR+ur4bddkaynnuq95dPKk4jVVf94kMkiM39qlApOJtM4NXJizhcRiqIP2434x0nRIPVDj+TRs/Tv/nZy+wlYqIWGu7HYvmyRUSI2nIc6BxeFW7Wn68uyUFqmysGYz4+bG6ftk2TfGDvc+2k6phEQXSRdvE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZTopPn3R; 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="ZTopPn3R" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAB14C4CEDD; Mon, 24 Mar 2025 18:13:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742840001; bh=HxL4j75EqQZXg4nUUxuhCgYtvVucbH/8DgVWCMZjacs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZTopPn3RAljPZx+g/g5IBXvkmaMMWchrjVzdIS5V9f1ViyUW54vubwIMO5krcXWTw OZ4UKGnqeSCBtW5zqETbG8Dd0YK/R0pzIruYv/EmUdSCCtWJt0AE6MZhKtzeMEllnx 1nWBCPV8k4QUXdNoaR8sVG6iVYagoSnYXXLAvwanO/tUfJCAyhyTNoNjdH31isHCPD TLjbvBDUkHiw89+DnTz5Lm8BjqUQ/GHT0yi9QwS5IrQ187nIIucvuA+jt99reEwYXz DOQINh8mr5aC1FeTB3dIzkvg02/s7PyItJ7fxP3Penwt/LXlpHBQ9sNuszRlsJnNQ7 deC1Xd8wYuDnQ== Date: Mon, 24 Mar 2025 19:13:15 +0100 From: Danilo Krummrich To: Benno Lossin Cc: Greg KH , bhelgaas@google.com, rafael@kernel.org, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, linux-pci@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/3] rust: pci: impl TryFrom<&Device> for &pci::Device Message-ID: References: <20250321214826.140946-1-dakr@kernel.org> <20250321214826.140946-3-dakr@kernel.org> <2025032158-embezzle-life-8810@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=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Mar 24, 2025 at 05:36:45PM +0000, Benno Lossin wrote: > On Mon Mar 24, 2025 at 5:49 PM CET, Danilo Krummrich wrote: > > On Mon, Mar 24, 2025 at 04:39:25PM +0000, Benno Lossin wrote: > >> On Sun Mar 23, 2025 at 11:10 PM CET, Danilo Krummrich wrote: > >> > On Sat, Mar 22, 2025 at 11:10:57AM +0100, Danilo Krummrich wrote: > >> >> On Fri, Mar 21, 2025 at 08:25:07PM -0700, Greg KH wrote: > >> >> > Along these lines, if you can convince me that this is something that we > >> >> > really should be doing, in that we should always be checking every time > >> >> > someone would want to call to_pci_dev(), that the return value is > >> >> > checked, then why don't we also do this in C if it's going to be > >> >> > something to assure people it is going to be correct? I don't want to > >> >> > see the rust and C sides get "out of sync" here for things that can be > >> >> > kept in sync, as that reduces the mental load of all of us as we travers > >> >> > across the boundry for the next 20+ years. > >> >> > >> >> I think in this case it is good when the C and Rust side get a bit > >> >> "out of sync": > >> > > >> > A bit more clarification on this: > >> > > >> > What I want to say with this is, since we can cover a lot of the common cases > >> > through abstractions and the type system, we're left with the not so common > >> > ones, where the "upcasts" are not made in the context of common and well > >> > established patterns, but, for instance, depend on the semantics of the driver; > >> > those should not be unsafe IMHO. > >> > >> I don't think that we should use `TryFrom` for stuff that should only be > >> used seldomly. A function that we can document properly is a much better > >> fit, since we can point users to the "correct" API. > > > > Most of the cases where drivers would do this conversion should be covered by > > the abstraction to already provide that actual bus specific device, rather than > > a generic one or some priv pointer, etc. > > > > So, the point is that the APIs we design won't leave drivers with a reason to > > make this conversion in the first place. For the cases where they have to > > (which should be rare), it's the right thing to do. There is not an alternative > > API to point to. > > Yes, but for such a case, I wouldn't want to use `TryFrom`, since that > trait to me is a sign of a canonical way to convert a value. Well, it is the canonical way to convert, it's just that by the design of other abstractions drivers should very rarely get in the situation of needing it in the first place.