[PATCH v2 5/5] rust: enable `clippy::as_underscore` lint

Tamir Duberstein
2025-03-09T16:01:19Z

In Rust 1.63.0, Clippy introduced the `as_underscore` lint [1]:

> The conversion might include lossy conversion or a dangerous cast that
> might go undetected due to the type being inferred.
>
> The lint is allowed by default as using `_` is less wordy than always
> specifying the type.

Always specifying the type is especially helpful in function call
contexts where the inferred type may change at a distance. Specifying
the type also allows Clippy to spot more cases of `useless_conversion`.

The primary downside is the need to specify the type in trivial getters.
There are 4 such functions: 3 have become slightly less ergonomic, 1 was
revealed to be a `useless_conversion`.

While this doesn't eliminate unchecked `as` conversions, it makes such
conversions easier to scrutinize. It also has the slight benefit of
removing a degree of freedom on which to bikeshed. Thus apply the
changes and enable the lint -- no functional change intended.

Link: https://rust-lang.github.io/rust-clippy/master/index.html#as_underscore [1]
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
Makefile | 1 +
rust/kernel/block/mq/operations.rs | 2 +-
rust/kernel/block/mq/request.rs | 2 +-
rust/kernel/device_id.rs | 2 +-
rust/kernel/devres.rs | 15 ++++++++-------
rust/kernel/error.rs | 2 +-
rust/kernel/firmware.rs | 2 +-
rust/kernel/io.rs | 18 +++++++++---------
rust/kernel/miscdevice.rs | 2 +-
rust/kernel/of.rs | 6 +++---
rust/kernel/pci.rs | 9 ++++++---
rust/kernel/str.rs | 8 ++++----
rust/kernel/workqueue.rs | 2 +-
13 files changed, 38 insertions(+), 33 deletions(-)

diff --git a/Makefile b/Makefile
index bb15b86182a3..2af40bfed9ce 100644
--- a/Makefile
+++ b/Makefile
@@ -478,6 +478,7 @@ export rust_common_flags := --edition=2021 \
-Wunreachable_pub \
-Wclippy::all \
-Wclippy::as_ptr_cast_mut \
+ -Wclippy::as_underscore \
-Wclippy::ignored_unit_patterns \
-Wclippy::mut_mut \
-Wclippy::needless_bitwise_bool \
diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs
index 864ff379dc91..d18ef55490da 100644
--- a/rust/kernel/block/mq/operations.rs
+++ b/rust/kernel/block/mq/operations.rs
@@ -101,7 +101,7 @@ impl<T: Operations> OperationsVTable<T> {
if let Err(e) = ret {
e.to_blk_status()
} else {
- bindings::BLK_STS_OK as _
+ bindings::BLK_STS_OK as u8
}
}

diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs
index 10c6d69be7f3..bcf2b73d9189 100644
--- a/rust/kernel/block/mq/request.rs
+++ b/rust/kernel/block/mq/request.rs
@@ -125,7 +125,7 @@ pub fn end_ok(this: ARef<Self>) -> Result<(), ARef<Self>> {
// success of the call to `try_set_end` guarantees that there are no
// `ARef`s pointing to this request. Therefore it is safe to hand it
// back to the block layer.
- unsafe { bindings::blk_mq_end_request(request_ptr, bindings::BLK_STS_OK as _) };
+ unsafe { bindings::blk_mq_end_request(request_ptr, bindings::BLK_STS_OK as u8) };

Ok(())
}
diff --git a/rust/kernel/device_id.rs b/rust/kernel/device_id.rs
index e5859217a579..4063f09d76d9 100644
--- a/rust/kernel/device_id.rs
+++ b/rust/kernel/device_id.rs
@@ -82,7 +82,7 @@ impl<T: RawDeviceId, U, const N: usize> IdArray<T, U, N> {
unsafe {
raw_ids[i]
.as_mut_ptr()
- .byte_offset(T::DRIVER_DATA_OFFSET as _)
+ .byte_add(T::DRIVER_DATA_OFFSET)
.cast::<usize>()
.write(i);
}
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 598001157293..20159b7c9293 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -45,7 +45,7 @@ struct DevresInner<T> {
/// # Example
///
/// ```no_run
-/// # use kernel::{bindings, c_str, device::Device, devres::Devres, io::{Io, IoRaw}};
+/// # use kernel::{bindings, c_str, device::Device, devres::Devres, ffi::c_void, io::{Io, IoRaw}};
/// # use core::ops::Deref;
///
/// // See also [`pci::Bar`] for a real example.
@@ -59,19 +59,19 @@ struct DevresInner<T> {
/// unsafe fn new(paddr: usize) -> Result<Self>{
/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
/// // valid for `ioremap`.
-/// let addr = unsafe { bindings::ioremap(paddr as _, SIZE as _) };
+/// let addr = unsafe { bindings::ioremap(paddr as u64, SIZE) };
/// if addr.is_null() {
/// return Err(ENOMEM);
/// }
///
-/// Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
+/// Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
/// }
/// }
///
/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
/// fn drop(&mut self) {
/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
-/// unsafe { bindings::iounmap(self.0.addr() as _); };
+/// unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
/// }
/// }
///
@@ -115,8 +115,9 @@ fn new(dev: &Device, data: T, flags: Flags) -> Result<Arc<DevresInner<T>>> {

// SAFETY: `devm_add_action` guarantees to call `Self::devres_callback` once `dev` is
// detached.
- let ret =
- unsafe { bindings::devm_add_action(dev.as_raw(), Some(inner.callback), data as _) };
+ let ret = unsafe {
+ bindings::devm_add_action(dev.as_raw(), Some(inner.callback), data.cast_mut().cast())
+ };

if ret != 0 {
// SAFETY: We just created another reference to `inner` in order to pass it to
@@ -130,7 +131,7 @@ fn new(dev: &Device, data: T, flags: Flags) -> Result<Arc<DevresInner<T>>> {
}

fn as_ptr(&self) -> *const Self {
- self as _
+ self
}

fn remove_action(this: &Arc<Self>) {
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 8654d52b0bb9..eb8fa52f08ba 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -152,7 +152,7 @@ pub(crate) fn to_blk_status(self) -> bindings::blk_status_t {
/// Returns the error encoded as a pointer.
pub fn to_ptr<T>(self) -> *mut T {
// SAFETY: `self.0` is a valid error due to its invariant.
- unsafe { bindings::ERR_PTR(self.0.get() as _).cast() }
+ unsafe { bindings::ERR_PTR(self.0.get() as isize).cast() }
}

/// Returns a string representing the error, if one exists.
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index c5162fdc95ff..9a279330261c 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -61,7 +61,7 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {

// SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
// `name` and `dev` are valid as by their type invariants.
- let ret = unsafe { func.0(pfw as _, name.as_char_ptr(), dev.as_raw()) };
+ let ret = unsafe { func.0(pfw, name.as_char_ptr(), dev.as_raw()) };
if ret != 0 {
return Err(Error::from_errno(ret));
}
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index d4a73e52e3ee..d375eed73dc8 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -5,7 +5,7 @@
//! C header: [`include/asm-generic/io.h`](srctree/include/asm-generic/io.h)

use crate::error::{code::EINVAL, Result};
-use crate::{bindings, build_assert};
+use crate::{bindings, build_assert, ffi::c_void};

/// Raw representation of an MMIO region.
///
@@ -56,7 +56,7 @@ pub fn maxsize(&self) -> usize {
/// # Examples
///
/// ```no_run
-/// # use kernel::{bindings, io::{Io, IoRaw}};
+/// # use kernel::{bindings, ffi::c_void, io::{Io, IoRaw}};
/// # use core::ops::Deref;
///
/// // See also [`pci::Bar`] for a real example.
@@ -70,19 +70,19 @@ pub fn maxsize(&self) -> usize {
/// unsafe fn new(paddr: usize) -> Result<Self>{
/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
/// // valid for `ioremap`.
-/// let addr = unsafe { bindings::ioremap(paddr as _, SIZE as _) };
+/// let addr = unsafe { bindings::ioremap(paddr as u64, SIZE) };
/// if addr.is_null() {
/// return Err(ENOMEM);
/// }
///
-/// Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
+/// Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
/// }
/// }
///
/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
/// fn drop(&mut self) {
/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
-/// unsafe { bindings::iounmap(self.0.addr() as _); };
+/// unsafe { bindings::iounmap(self.0.addr() as *mut c_void); };
/// }
/// }
///
@@ -119,7 +119,7 @@ pub fn $name(&self, offset: usize) -> $type_name {
let addr = self.io_addr_assert::<$type_name>(offset);

// SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
- unsafe { bindings::$name(addr as _) }
+ unsafe { bindings::$name(addr as *const c_void) }
}

/// Read IO data from a given offset.
@@ -131,7 +131,7 @@ pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
let addr = self.io_addr::<$type_name>(offset)?;

// SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
- Ok(unsafe { bindings::$name(addr as _) })
+ Ok(unsafe { bindings::$name(addr as *const c_void) })
}
};
}
@@ -148,7 +148,7 @@ pub fn $name(&self, value: $type_name, offset: usize) {
let addr = self.io_addr_assert::<$type_name>(offset);

// SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
- unsafe { bindings::$name(value, addr as _, ) }
+ unsafe { bindings::$name(value, addr as *mut c_void) }
}

/// Write IO data from a given offset.
@@ -160,7 +160,7 @@ pub fn $try_name(&self, value: $type_name, offset: usize) -> Result {
let addr = self.io_addr::<$type_name>(offset)?;

// SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
- unsafe { bindings::$name(value, addr as _) }
+ unsafe { bindings::$name(value, addr as *mut c_void) }
Ok(())
}
};
diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index e14433b2ab9d..2c66e926bffb 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -33,7 +33,7 @@ impl MiscDeviceOptions {
pub const fn into_raw<T: MiscDevice>(self) -> bindings::miscdevice {
// SAFETY: All zeros is valid for this C type.
let mut result: bindings::miscdevice = unsafe { MaybeUninit::zeroed().assume_init() };
- result.minor = bindings::MISC_DYNAMIC_MINOR as _;
+ result.minor = bindings::MISC_DYNAMIC_MINOR as i32;
result.name = self.name.as_char_ptr();
result.fops = create_vtable::<T>();
result
diff --git a/rust/kernel/of.rs b/rust/kernel/of.rs
index 04f2d8ef29cb..40d1bd13682c 100644
--- a/rust/kernel/of.rs
+++ b/rust/kernel/of.rs
@@ -22,7 +22,7 @@ unsafe impl RawDeviceId for DeviceId {
const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::of_device_id, data);

fn index(&self) -> usize {
- self.0.data as _
+ self.0.data as usize
}
}

@@ -34,10 +34,10 @@ pub const fn new(compatible: &'static CStr) -> Self {
// SAFETY: FFI type is valid to be zero-initialized.
let mut of: bindings::of_device_id = unsafe { core::mem::zeroed() };

- // TODO: Use `clone_from_slice` once the corresponding types do match.
+ // TODO: Use `copy_from_slice` once stabilized for `const`.
let mut i = 0;
while i < src.len() {
- of.compatible[i] = src[i] as _;
+ of.compatible[i] = src[i];
i += 1;
}

diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 63218abb7a25..a925732f6c7a 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -166,7 +166,7 @@ unsafe impl RawDeviceId for DeviceId {
const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::pci_device_id, driver_data);

fn index(&self) -> usize {
- self.0.driver_data as _
+ self.0.driver_data
}
}

@@ -201,7 +201,10 @@ macro_rules! pci_device_table {
/// MODULE_PCI_TABLE,
/// <MyDriver as pci::Driver>::IdInfo,
/// [
-/// (pci::DeviceId::from_id(bindings::PCI_VENDOR_ID_REDHAT, bindings::PCI_ANY_ID as _), ())
+/// (
+/// pci::DeviceId::from_id(bindings::PCI_VENDOR_ID_REDHAT, bindings::PCI_ANY_ID as u32),
+/// (),
+/// )
/// ]
/// );
///
@@ -317,7 +320,7 @@ unsafe fn do_release(pdev: &Device, ioptr: usize, num: i32) {
// `ioptr` is valid by the safety requirements.
// `num` is valid by the safety requirements.
unsafe {
- bindings::pci_iounmap(pdev.as_raw(), ioptr as _);
+ bindings::pci_iounmap(pdev.as_raw(), ioptr as *mut kernel::ffi::c_void);
bindings::pci_release_region(pdev.as_raw(), num);
}
}
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 6a1a982b946d..0b80a119d5f0 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -692,9 +692,9 @@ fn new() -> Self {
pub(crate) unsafe fn from_ptrs(pos: *mut u8, end: *mut u8) -> Self {
// INVARIANT: The safety requirements guarantee the type invariants.
Self {
- beg: pos as _,
- pos: pos as _,
- end: end as _,
+ beg: pos as usize,
+ pos: pos as usize,
+ end: end as usize,
}
}

@@ -719,7 +719,7 @@ pub(crate) unsafe fn from_buffer(buf: *mut u8, len: usize) -> Self {
///
/// N.B. It may point to invalid memory.
pub(crate) fn pos(&self) -> *mut u8 {
- self.pos as _
+ self.pos as *mut u8
}

/// Returns the number of bytes written to the formatter.
diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 8ff54105be3f..d03f3440cb5a 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -198,7 +198,7 @@ pub fn enqueue<W, const ID: u64>(&self, w: W) -> W::EnqueueOutput
unsafe {
w.__enqueue(move |work_ptr| {
bindings::queue_work_on(
- bindings::wq_misc_consts_WORK_CPU_UNBOUND as _,
+ bindings::wq_misc_consts_WORK_CPU_UNBOUND as i32,
queue_ptr,
work_ptr,
)

--
2.48.1