From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from forward502a.mail.yandex.net (forward502a.mail.yandex.net [178.154.239.82]) (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 0610F10E3; Tue, 9 Sep 2025 15:45:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.154.239.82 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757432741; cv=none; b=UvQ2XsVibGQWFuLRUGHLItJTTUYDgB3iSiKxquiulTescB+Jv1CSkjjRWrc0aZXO1tVSx4zD48izTRZSPJTNP1KMPpkToYUfvHbPeBTwSkidwIt2cEpHlOX7CvQ2jkeiuGF3ynuhW/ckT/Yi3VJBBC1Rs/X85ftxHgtAphIJqN4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757432741; c=relaxed/simple; bh=0yz6aghSeYaaRKdDcRzSd6f06S1jGRsDA2q9Dz/HqU0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=URzjsjczV8dwomxywESdqXhfiiYPkZznjtujLdVUP6tHP3cqJgDXPstIRz2NCoRkSh9k03LHVCXnWwmL94IEbIgOT1sMniRJ1IcNFAN5bsGTbzCVU/C/Dcepa8+6LJp/hxgCXdZpm5NnXeh+PSAP/9YUly3m9KHq4JC/Og2+Ir0= 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=fuU63Asy; arc=none smtp.client-ip=178.154.239.82 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="fuU63Asy" Received: from mail-nwsmtp-smtp-production-main-94.vla.yp-c.yandex.net (mail-nwsmtp-smtp-production-main-94.vla.yp-c.yandex.net [IPv6:2a02:6b8:c15:290e:0:640:f317:0]) by forward502a.mail.yandex.net (Yandex) with ESMTPS id E9F59809BE; Tue, 09 Sep 2025 18:45:28 +0300 (MSK) Received: by mail-nwsmtp-smtp-production-main-94.vla.yp-c.yandex.net (smtp/Yandex) with ESMTPSA id OjLILl4LuKo0-8eHHkWSo; Tue, 09 Sep 2025 18:45:28 +0300 X-Yandex-Fwd: 1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=onurozkan.dev; s=mail; t=1757432728; bh=dIRrBjelZrgFNCTCF1oaGTQ+9cRVwzvwxL9eis2Nb8E=; h=Cc:Message-ID:Subject:Date:References:To:From:In-Reply-To; b=fuU63Asya9b0JbIYNjWzZzCcVMoi+Tx7cRLs4YuTE/BS5B35N6B56Ysrr7iT/TguE E2CH4qM5gHSya4oemztI7rw+OXVrG2LtmoM2te+0Tio2HcL4j809YmaSusc+AA27z9 QkLj7iC1iv7ZrtQwVv1nD8Cv4IUY/8qe64AJOMJo= Authentication-Results: mail-nwsmtp-smtp-production-main-94.vla.yp-c.yandex.net; dkim=pass header.i=@onurozkan.dev Date: Tue, 9 Sep 2025 18:45:24 +0300 From: Onur 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 v1] rust: refactor `to_result` to return the original value Message-ID: <20250909184524.1482d602@nimda.home> In-Reply-To: References: <20250909123258.29304-1-work@onurozkan.dev> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.50; 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 Tue, 9 Sep 2025 14:36:13 +0200 Alice Ryhl wrote: > On Tue, Sep 9, 2025 at 2:33=E2=80=AFPM Onur =C3=96zkan wrote: > > > > Current `to_result` helper takes a `c_int` and returns `Ok(())` on > > success and this has some issues like: > > > > - Callers lose the original return value and often have to store > > it in a temporary variable before calling `to_result`. > > > > - 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]). > > > > [0]: https://lore.kernel.org/all/20250822080252.773d6f54@nimda.home/ > > > > This patch changes `to_result` to be generic and also return the > > original value on success. > > > > So that the code that previously looked like: > > > > let ret =3D unsafe { bindings::some_ffi_call() }; > > to_result(ret).map(|()| SomeType::new(ret)) > > > > can now be written more directly as: > > > > to_result(unsafe { bindings::some_ffi_call() }) > > .map(|ret| SomeType::new(ret)) > > > > Similarly, code such as: > > > > let res: isize =3D $some_ffi_call(); > > if res < 0 { > > return Err(Error::from_errno(res as i32)); > > } > > > > can now be used with `to_result` as: > > > > to_result($some_ffi_call())?; > > > > Existing call sites that only care about success/failure are updated > > to append `.map(|_| ())` to preserve their previous semantics. They > > can also use the equivalent pattern: > > > > to_result($something)?; > > Ok(()) > > > > 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. > > > > [1]: https://lore.kernel.org/rust-for-linux/?q=3Dto_result > > [2]: https://github.com/Rust-for-Linux/linux > > > > Link: > > https://rust-for-linux.zulipchat.com/#narrow/channel/288089/topic/x/nea= r/536374456 > > Signed-off-by: Onur =C3=96zkan --- > > rust/kernel/auxiliary.rs | 1 + > > rust/kernel/block/mq/tag_set.rs | 2 +- > > rust/kernel/cpufreq.rs | 3 ++- > > rust/kernel/devres.rs | 1 + > > rust/kernel/dma.rs | 3 +++ > > rust/kernel/error.rs | 17 ++++++++++++----- > > rust/kernel/miscdevice.rs | 2 +- > > rust/kernel/mm/virt.rs | 1 + > > rust/kernel/pci.rs | 3 ++- > > rust/kernel/platform.rs | 2 +- > > rust/kernel/regulator.rs | 5 +++-- > > 11 files changed, 28 insertions(+), 12 deletions(-) > > > > diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs > > index 4749fb6bffef..479c0ad2a572 100644 > > --- a/rust/kernel/auxiliary.rs > > +++ b/rust/kernel/auxiliary.rs > > @@ -43,6 +43,7 @@ unsafe fn register( > > to_result(unsafe { > > bindings::__auxiliary_driver_register(adrv.get(), > > module.0, name.as_char_ptr()) }) > > + .map(|_| ()) > > } > > > > unsafe fn unregister(adrv: &Opaque) { > > diff --git a/rust/kernel/block/mq/tag_set.rs > > b/rust/kernel/block/mq/tag_set.rs index c3cf56d52bee..0e7883163000 > > 100644 --- a/rust/kernel/block/mq/tag_set.rs > > +++ b/rust/kernel/block/mq/tag_set.rs > > @@ -65,7 +65,7 @@ pub fn new( > > // SAFETY: we do not move out of `tag_set`. > > let tag_set: &mut Opaque<_> =3D unsafe { > > Pin::get_unchecked_mut(tag_set) }; // SAFETY: `tag_set` is a > > reference to an initialized `blk_mq_tag_set`. > > - error::to_result( unsafe { > > bindings::blk_mq_alloc_tag_set(tag_set.get())}) > > + error::to_result( unsafe { > > bindings::blk_mq_alloc_tag_set(tag_set.get())}).map(|_| ()) }), > > _p: PhantomData, > > }) > > diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs > > index be2dffbdb546..c3fa20ce229a 100644 > > --- a/rust/kernel/cpufreq.rs > > +++ b/rust/kernel/cpufreq.rs > > @@ -157,6 +157,7 @@ pub fn as_raw(&self) -> *mut > > bindings::cpufreq_policy_data { pub fn generic_verify(&self) -> > > Result { // SAFETY: By the type invariant, the pointer stored in > > `self` is valid. to_result(unsafe { > > bindings::cpufreq_generic_frequency_table_verify(self.as_raw()) }) > > + .map(|_| ()) > > } > > } > > > > @@ -519,7 +520,7 @@ pub fn set_suspend_freq(&mut self, freq: Hertz) > > -> &mut Self { #[inline] > > pub fn generic_suspend(&mut self) -> Result { > > // SAFETY: By the type invariant, the pointer stored in > > `self` is valid. > > - to_result(unsafe { > > bindings::cpufreq_generic_suspend(self.as_mut_ref()) }) > > + to_result(unsafe { > > bindings::cpufreq_generic_suspend(self.as_mut_ref()) }).map(|_| ()) > > } > > > > /// Provides a wrapper to the generic get routine. > > diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs > > index d04e3fcebafb..214cd9a0ebe0 100644 > > --- a/rust/kernel/devres.rs > > +++ b/rust/kernel/devres.rs > > @@ -328,6 +328,7 @@ fn register_foreign

(dev: &Device, > > data: P) -> Result // `ForeignOwnable` is released eventually. > > bindings::devm_add_action_or_reset(dev.as_raw(), > > Some(callback::

), ptr.cast()) }) > > + .map(|_| ()) > > } > > > > /// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` > > once `dev` is unbound. diff --git a/rust/kernel/dma.rs > > b/rust/kernel/dma.rs index 68fe67624424..f614453ddb7d 100644 > > --- a/rust/kernel/dma.rs > > +++ b/rust/kernel/dma.rs > > @@ -34,6 +34,7 @@ unsafe fn dma_set_mask(&self, mask: DmaMask) -> > > Result { // - The safety requirement of this function guarantees > > that there are no concurrent calls // to DMA allocation and > > mapping primitives using this mask. to_result(unsafe { > > bindings::dma_set_mask(self.as_ref().as_raw(), mask.value()) }) > > + .map(|_| ()) > > } > > > > /// Set up the device's DMA coherent addressing capabilities. > > @@ -51,6 +52,7 @@ unsafe fn dma_set_coherent_mask(&self, mask: > > DmaMask) -> Result { // - The safety requirement of this function > > guarantees that there are no concurrent calls // to DMA > > allocation and mapping primitives using this mask. to_result(unsafe > > { bindings::dma_set_coherent_mask(self.as_ref().as_raw(), > > mask.value()) }) > > + .map(|_| ()) > > } > > > > /// Set up the device's DMA addressing capabilities. > > @@ -72,6 +74,7 @@ unsafe fn dma_set_mask_and_coherent(&self, mask: > > DmaMask) -> Result { to_result(unsafe { > > bindings::dma_set_mask_and_coherent(self.as_ref().as_raw(), > > mask.value()) }) > > + .map(|_| ()) > > } > > } > > > > diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs > > index db14da976722..f76afa4b7ec1 100644 > > --- a/rust/kernel/error.rs > > +++ b/rust/kernel/error.rs > > @@ -378,12 +378,19 @@ fn from(e: core::convert::Infallible) -> > > Error { pub type Result =3D > > core::result::Result; > > > > /// 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) > > } > > } > > > > 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(|_| ()) }), > > _t: PhantomData, > > }) > > diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs > > index a1bfa4e19293..5494f96e91b0 100644 > > --- a/rust/kernel/mm/virt.rs > > +++ b/rust/kernel/mm/virt.rs > > @@ -195,6 +195,7 @@ pub fn vm_insert_page(&self, address: usize, > > page: &Page) -> Result { // SAFETY: By the type invariant of `Self` > > caller has read access and has verified that // `VM_MIXEDMAP` is > > set. By invariant on `Page` the page has order 0. to_result(unsafe > > { bindings::vm_insert_page(self.as_ptr(), address, page.as_ptr()) }) > > + .map(|_| ()) > > } > > } > > > > diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs > > index 887ee611b553..6e917752cb89 100644 > > --- a/rust/kernel/pci.rs > > +++ b/rust/kernel/pci.rs > > @@ -48,6 +48,7 @@ unsafe fn register( > > to_result(unsafe { > > bindings::__pci_register_driver(pdrv.get(), module.0, > > name.as_char_ptr()) }) > > + .map(|_| ()) > > } > > > > unsafe fn unregister(pdrv: &Opaque) { > > @@ -437,7 +438,7 @@ impl Device { > > /// Enable memory resources for this device. > > pub fn enable_device_mem(&self) -> Result { > > // SAFETY: `self.as_raw` is guaranteed to be a pointer to > > a valid `struct pci_dev`. > > - to_result(unsafe { > > bindings::pci_enable_device_mem(self.as_raw()) }) > > + to_result(unsafe { > > bindings::pci_enable_device_mem(self.as_raw()) }).map(|_| ()) } > > > > /// Enable bus-mastering for this device. > > diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs > > index 8f028c76f9fa..5a5561c7326e 100644 > > --- a/rust/kernel/platform.rs > > +++ b/rust/kernel/platform.rs > > @@ -54,7 +54,7 @@ unsafe fn register( > > } > > > > // SAFETY: `pdrv` is guaranteed to be a valid `RegType`. > > - to_result(unsafe { > > bindings::__platform_driver_register(pdrv.get(), module.0) }) > > + to_result(unsafe { > > bindings::__platform_driver_register(pdrv.get(), module.0) > > }).map(|_| ()) } > > > > unsafe fn unregister(pdrv: &Opaque) { > > diff --git a/rust/kernel/regulator.rs b/rust/kernel/regulator.rs > > index 65f3a125348f..e17ae6e9a990 100644 > > --- a/rust/kernel/regulator.rs > > +++ b/rust/kernel/regulator.rs > > @@ -261,6 +261,7 @@ pub fn set_voltage(&self, min_voltage: Voltage, > > max_voltage: Voltage) -> Result max_voltage.as_microvolts(), > > ) > > }) > > + .map(|_| ()) > > } > > > > /// Gets the current voltage of the regulator. > > @@ -291,12 +292,12 @@ fn get_internal(dev: &Device, name: &CStr) -> > > Result> { > > > > fn enable_internal(&mut self) -> Result { > > // SAFETY: Safe as per the type invariants of `Regulator`. > > - to_result(unsafe { > > bindings::regulator_enable(self.inner.as_ptr()) }) > > + to_result(unsafe { > > bindings::regulator_enable(self.inner.as_ptr()) }).map(|_| ()) } > > > > fn disable_internal(&mut self) -> Result { > > // SAFETY: Safe as per the type invariants of `Regulator`. > > - to_result(unsafe { > > bindings::regulator_disable(self.inner.as_ptr()) }) > > + to_result(unsafe { > > bindings::regulator_disable(self.inner.as_ptr()) }).map(|_| ()) >=20 > IMO all of the new map calls in this patch should use the >=20 > to_result(...)? > Ok(()) >=20 > syntax. >=20 > Alice Agreed, will do it in v2. -Onur