From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from forward502d.mail.yandex.net (forward502d.mail.yandex.net [178.154.239.210]) (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 CB3F318FC97; Wed, 10 Sep 2025 10:59:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.154.239.210 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757501945; cv=none; b=TEEB358z55H/ZQyS99Jefv/niWNd+E3+iWXyNvC15xv83b4Vf+bT0nJnsRGqLKvjHlVwYkbDhTh1hCBC2KAee6UY0XG39YV/3/1GSJJhBJAeByRcKvgK1KtnX4/F/VHX88HDH2EX9Iao8WWT6zEYpj4K51DhCIEsAgMSfrEj8Zo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757501945; c=relaxed/simple; bh=LfkW7+godablUCnUw+RxZ0UOcEJognGUZ7Oi6euYX6s=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=sb4iasDor6fBO+D/hCbchp/JNBI7w9MyWRon5o3ycd+caWw/vbnHr0ySf+swFMnVPzqEsPPxJzE2LKfKhiMWnn1wcBebNJ+eHpXpiz2VZF31i8dgEh0DEI58sxXvUZE3soiNaC5NjpV6oX8emtRzokrsG4/CASOkn31OGQbtWDw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=onurozkan.dev; spf=pass smtp.mailfrom=onurozkan.dev; dkim=pass (1024-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b=UrKSKuIr; arc=none smtp.client-ip=178.154.239.210 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=onurozkan.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=onurozkan.dev header.i=@onurozkan.dev header.b="UrKSKuIr" Received: from mail-nwsmtp-smtp-production-main-69.iva.yp-c.yandex.net (mail-nwsmtp-smtp-production-main-69.iva.yp-c.yandex.net [IPv6:2a02:6b8:c0c:160e:0:640:2589:0]) by forward502d.mail.yandex.net (Yandex) with ESMTPS id 47338C1B86; Wed, 10 Sep 2025 13:58:59 +0300 (MSK) Received: by mail-nwsmtp-smtp-production-main-69.iva.yp-c.yandex.net (smtp/Yandex) with ESMTPSA id swHnkSBMu4Y0-y2KfdKi4; Wed, 10 Sep 2025 13:58:58 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=onurozkan.dev; s=mail; t=1757501938; bh=kZkUcDMg2LSkPRZlDUL3r2d6ErfJziliT14Z/IR233U=; h=Cc:Message-ID:Subject:Date:References:To:From:In-Reply-To; b=UrKSKuIrxHYb1+h0+94ynqGVVpYqK0Z6h6YsOym3y2p8LMhZUz2UYjnS4QdvmeNtx u/X+9ozZpfjHWwuzbea+Aw3bP5/iwua+m4Lqes/M9A8+UmVoh8/6T5iKQ1dR6Pv+RI zPKPP11A8rYUewOO5tTbp67ebJmk5L3EpshtABaA= Authentication-Results: mail-nwsmtp-smtp-production-main-69.iva.yp-c.yandex.net; dkim=pass header.i=@onurozkan.dev Date: Wed, 10 Sep 2025 13:58:48 +0300 From: Onur =?UTF-8?B?w5Z6a2Fu?= To: Alice Ryhl Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, daniel@sedlak.dev, dirk.behme@de.bosch.com, felipe_life@live.com, tamird@gmail.com, dakr@kernel.org, tmgross@umich.edu, a.hindborg@kernel.org, lossin@kernel.org, bjorn3_gh@protonmail.com, gary@garyguo.net, boqun.feng@gmail.com, alex.gaynor@gmail.com, ojeda@kernel.org Subject: Re: [PATCH v2 1/1] rust: refactor to_result to return the original value Message-ID: <20250910135848.1ea11519@nimda.home> In-Reply-To: References: <20250909170013.16025-1-work@onurozkan.dev> <20250909170013.16025-2-work@onurozkan.dev> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-unknown-linux-gnu) 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-Transfer-Encoding: quoted-printable On Wed, 10 Sep 2025 06:26:27 +0000 Alice Ryhl wrote: > On Tue, Sep 09, 2025 at 08:00:13PM +0300, Onur =C3=96zkan wrote: > > Current `to_result` helper takes a `c_int` and returns `Ok(())` on > > success and this has some issues like: > >=20 > > - Callers lose the original return value and often have to store > > it in a temporary variable before calling `to_result`. > >=20 > > - It only supports `c_int`, which makes callers to unnecessarily > > cast when working with other types (e.g. `u16` in phy > > abstractions). We even have some places that ignore to use > > `to_result` helper because the input doesn't fit in `c_int` > > (see [0]). > >=20 > > [0]: https://lore.kernel.org/all/20250822080252.773d6f54@nimda.home/ > >=20 > > This patch changes `to_result` to be generic and also return the > > original value on success. > >=20 > > So that the code that previously looked like: > >=20 > > let ret =3D unsafe { bindings::some_ffi_call() }; > > to_result(ret).map(|()| SomeType::new(ret)) > >=20 > > can now be written more directly as: > >=20 > > to_result(unsafe { bindings::some_ffi_call() }) > > .map(|ret| SomeType::new(ret)) > >=20 > > Similarly, code such as: > >=20 > > let res: isize =3D $some_ffi_call(); > > if res < 0 { > > return Err(Error::from_errno(res as i32)); > > } > >=20 > > can now be used with `to_result` as: > >=20 > > to_result($some_ffi_call())?; > >=20 > > This patch only fixes the callers that broke after the changes on > > `to_result`. I haven't included all the improvements made possible > > by the new design since that could conflict with other ongoing > > patches [1]. Once this patch is approved and applied, I am planning > > to follow up with creating a "good first issue" on [2] for those > > additional changes. > >=20 > > [1]: https://lore.kernel.org/rust-for-linux/?q=3Dto_result > > [2]: https://github.com/Rust-for-Linux/linux > >=20 > > Link: > > https://rust-for-linux.zulipchat.com/#narrow/channel/288089/topic/x/nea= r/536374456 > > Signed-off-by: Onur =C3=96zkan >=20 > > diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs > > index a41de293dcd1..6563ea71e203 100644 > > --- a/rust/kernel/error.rs > > +++ b/rust/kernel/error.rs > > @@ -376,12 +376,19 @@ fn from(e: core::convert::Infallible) -> > > Error { pub type Result =3D > > core::result::Result; > >=20 > > /// Converts an integer as returned by a C kernel function to an > > error if it's negative, and -/// `Ok(())` otherwise. > > -pub fn to_result(err: crate::ffi::c_int) -> Result { > > - if err < 0 { > > - Err(Error::from_errno(err)) > > +/// returns the original value otherwise. > > +pub fn to_result(code: T) -> Result > > +where > > + T: Copy + TryInto, > > +{ > > + // Try casting into `i32`. > > + let casted: crate::ffi::c_int =3D code.try_into().unwrap_or(0); > > + > > + if casted < 0 { > > + Err(Error::from_errno(casted)) > > } else { > > - Ok(()) > > + // Return the original input value. > > + Ok(code) > > } > > } >=20 > I don't think this is the best way to declare this function. The > conversions I would want are: >=20 > * i32 -> Result > * isize -> Result > * i64 -> Result >=20 > Your commit messages mentions i16, but does the error types even fit > in 16 bits? Maybe. But they don't fit in i8. That is to say, I think > it should support all the types larger than i32 (the errors fit in > those types too), but for the ones that are smaller, it might not > make sense if the type is too small. That's the reverse of what you > have now. >=20 > We probably need a new trait. E.g.: >=20 > trait ToResult { > type Unsigned; > fn to_result(self) -> Result; > } >=20 > impl ToResult for i32 { > type Unsigned =3D u32; > fn to_result(self) -> Result { > ... > } > } >=20 > impl ToResult for isize { > type Unsigned =3D usize; > fn to_result(self) -> Result { > ... > } > } >=20 > pub fn to_result(code: T) -> Result { > T::to_result(code) > } >=20 `Error::from_errno` is limited to i32, that's why I followed the `TryInto` approach, but I like this design too. > > diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs > > index 6373fe183b27..22b72ae84c03 100644 > > --- a/rust/kernel/miscdevice.rs > > +++ b/rust/kernel/miscdevice.rs > > @@ -79,7 +79,7 @@ pub fn register(opts: MiscDeviceOptions) -> impl > > PinInit { // the destructor of this type deallocates > > the memory. // INVARIANT: If this returns `Ok(())`, then the `slot` > > will contain a registered // misc device. > > - to_result(unsafe { bindings::misc_register(slot) }) > > + to_result(unsafe { bindings::misc_register(slot) > > }).map(|_| ()) >=20 > This still uses the `map` pattern. Please change it too. >=20 > Alice I left that part intentionally and explained the reason in v2 changelog. Thanks, Onur