[PATCH v11 1/2] rust: input: add input device abstractions

[Vecheslav Filatov <harepro29@gmail.com>]

Add safe Rust abstractions for Linux input devices (struct input_dev).

This provides:
- `AllocatedDevice`: a newly allocated, unregistered input device handle
  that allows configuring capabilities (keys, absolute axis limits, parent
  device) before registration.
- Safe string methods: `set_name` and `set_phys` accept `&'static CStr`
  to prevent use-after-free since the input core does not copy strings.
- `set_phys_from_parent`: dynamic physical location path formatting
  ("%s/input0") stored safely in an owned kernel heap buffer.
- Device lifecycle and reference count management: `set_parent` takes
  a reference count via `bindings::get_device` to avoid dangling pointers,
  releasing it appropriately on drop or post-registration.
- Bounds-checked `set_abs_params` validating `axis < ABS_CNT` (0x40)
  to prevent memory corruption in `dev->absinfo`.
- `RegisteredDevice`: a registered input device handle providing safe,
  inlined methods to report keys, absolute coordinates, and synchronization
  events. Automatically calls `input_unregister_device` on drop (RAII).
- Constants for bus types (`bus::*`) and event types (`event_type::*`).
- Alphabetically sorted imports and module entries gated with
  `#[cfg(CONFIG_INPUT = "y")]` and `#if IS_REACHABLE(CONFIG_INPUT)`
  to avoid link failures when CONFIG_INPUT is disabled or modular.

Signed-off-by: Vecheslav Filatov <harepro29@gmail.com>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/helpers.c          |   1 +
 rust/helpers/input.c            |  22 +++
 rust/kernel/input.rs            | 253 ++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   2 +
 5 files changed, 279 insertions(+)
 create mode 100644 rust/helpers/input.c
 create mode 100644 rust/kernel/input.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 3791af0aadc7..4b09d3980e10 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -64,6 +64,7 @@
 #include <linux/fwctl.h>
 #include <linux/fs.h>
 #include <linux/i2c.h>
+#include <linux/input.h>
 #include <linux/interrupt.h>
 #include <linux/io-pgtable.h>
 #include <linux/ioport.h>
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index d62c7be1ca7b..77cec85ad153 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -67,6 +67,7 @@
 #include "fs.c"
 #include "fwctl.c"
 #include "gpu.c"
+#include "input.c"
 #include "interrupt.c"
 #include "io.c"
 #include "irq.c"
diff --git a/rust/helpers/input.c b/rust/helpers/input.c
new file mode 100644
index 000000000000..f43a06acfdc3
--- /dev/null
+++ b/rust/helpers/input.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/input.h>
+
+#if IS_REACHABLE(CONFIG_INPUT)
+
+__rust_helper void rust_helper_input_report_key(struct input_dev *dev, unsigned int code, int value)
+{
+	input_report_key(dev, code, value);
+}
+
+__rust_helper void rust_helper_input_report_abs(struct input_dev *dev, unsigned int code, int value)
+{
+	input_report_abs(dev, code, value);
+}
+
+__rust_helper void rust_helper_input_sync(struct input_dev *dev)
+{
+	input_sync(dev);
+}
+
+#endif /* IS_REACHABLE(CONFIG_INPUT) */
diff --git a/rust/kernel/input.rs b/rust/kernel/input.rs
new file mode 100644
index 000000000000..14977298ad47
--- /dev/null
+++ b/rust/kernel/input.rs
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Input subsystem abstractions for safe Rust drivers.
+//!
+//! Provides a safe Rust object-oriented interface around Linux `struct input_dev`,
+//! ensuring safe allocation, capability configuration, registration, and RAII cleanup.
+
+use crate::{
+    bindings,         //
+    device,           //
+    error::to_result, //
+    prelude::*,       //
+};
+use core::ptr::NonNull;
+
+/// Bus types for input devices.
+pub mod bus {
+    use super::*;
+
+    /// PCI bus.
+    pub const PCI: u16 = bindings::BUS_PCI as u16;
+    /// USB bus.
+    pub const USB: u16 = bindings::BUS_USB as u16;
+    /// RS232 serial bus.
+    pub const RS232: u16 = bindings::BUS_RS232 as u16;
+}
+
+/// Event types reported by input devices.
+pub mod event_type {
+    use super::*;
+
+    /// Key or button press/release events.
+    pub const KEY: u32 = bindings::EV_KEY;
+    /// Absolute axis movement events.
+    pub const ABS: u32 = bindings::EV_ABS;
+}
+
+/// An allocated input device being configured prior to registration.
+pub struct AllocatedDevice {
+    ptr: NonNull<bindings::input_dev>,
+    phys: Option<KBox<[u8; 64]>>,
+}
+
+impl AllocatedDevice {
+    /// Allocates a new input device.
+    #[inline]
+    pub fn new() -> Result<Self> {
+        // SAFETY: `input_allocate_device` returns either a valid pointer or NULL.
+        let ptr = unsafe { bindings::input_allocate_device() };
+        let ptr = NonNull::new(ptr).ok_or(ENOMEM)?;
+
+        Ok(Self { ptr, phys: None })
+    }
+
+    /// Sets the human-readable device name.
+    #[inline]
+    pub fn set_name(&mut self, name: &'static CStr) {
+        // SAFETY: `self.ptr` is valid and `name` has static lifetime.
+        unsafe {
+            (*self.ptr.as_ptr()).name = name.as_char_ptr().cast();
+        }
+    }
+
+    /// Sets the physical location string from a static C string.
+    #[inline]
+    pub fn set_phys(&mut self, phys: &'static CStr) {
+        // SAFETY: `self.ptr` is valid and `phys` has static lifetime.
+        unsafe {
+            (*self.ptr.as_ptr()).phys = phys.as_char_ptr().cast();
+        }
+    }
+
+    /// Sets the physical location string by formatting `<parent_phys>/input0`.
+    #[inline]
+    pub fn set_phys_from_parent(&mut self, parent_phys: &[u8]) -> Result {
+        let mut buf = KBox::new([0u8; 64], GFP_KERNEL)?;
+        let len = parent_phys
+            .iter()
+            .position(|&b| b == 0)
+            .unwrap_or(parent_phys.len());
+        let suffix = b"/input0\0";
+        if len + suffix.len() > buf.len() {
+            return Err(EINVAL);
+        }
+        buf[..len].copy_from_slice(&parent_phys[..len]);
+        buf[len..len + suffix.len()].copy_from_slice(suffix);
+
+        // SAFETY: `buf` is allocated on the kernel heap and its lifetime is tied to `self.phys`.
+        unsafe {
+            (*self.ptr.as_ptr()).phys = buf.as_ptr().cast();
+        }
+        self.phys = Some(buf);
+        Ok(())
+    }
+
+    /// Sets device identifier (bus type, vendor, product, version).
+    #[inline]
+    pub fn set_id(&mut self, bustype: u16, vendor: u16, product: u16, version: u16) {
+        // SAFETY: `self.ptr` is valid.
+        unsafe {
+            let dev = self.ptr.as_ptr();
+            (*dev).id.bustype = bustype;
+            (*dev).id.vendor = vendor;
+            (*dev).id.product = product;
+            (*dev).id.version = version;
+        }
+    }
+
+    /// Sets the parent device for this input device.
+    ///
+    /// Holds a reference count on `parent` to prevent dangling pointers before registration.
+    #[inline]
+    pub fn set_parent(&mut self, parent: &device::Device) {
+        // SAFETY: `self.ptr` is valid, and `parent.as_raw()` returns a valid `struct device`.
+        // Acquire a reference to guarantee `parent` remains alive while referenced by `dev.parent`.
+        unsafe {
+            let old = (*self.ptr.as_ptr()).dev.parent;
+            if !old.is_null() {
+                bindings::put_device(old);
+            }
+            (*self.ptr.as_ptr()).dev.parent = bindings::get_device(parent.as_raw());
+        }
+    }
+
+    /// Enables support for a capability (e.g. key or axis).
+    #[inline]
+    pub fn set_capability(&mut self, type_: u32, code: u32) {
+        // SAFETY: `self.ptr` is valid and type/code are valid capability values.
+        unsafe {
+            bindings::input_set_capability(self.ptr.as_ptr(), type_, code);
+        }
+    }
+
+    /// Sets parameter limits for an absolute axis.
+    ///
+    /// Bounds-checks `axis < ABS_CNT` (0x40) to prevent out-of-bounds writes
+    /// to the `absinfo` array in `struct input_dev`.
+    #[inline]
+    pub fn set_abs_params(
+        &mut self,
+        axis: u32,
+        min: i32,
+        max: i32,
+        fuzz: i32,
+        flat: i32,
+    ) -> Result {
+        if axis >= bindings::ABS_CNT {
+            return Err(EINVAL);
+        }
+
+        // SAFETY: `self.ptr` is valid and `axis` has been verified within bounds.
+        unsafe {
+            bindings::input_set_abs_params(self.ptr.as_ptr(), axis, min, max, fuzz, flat);
+        }
+        Ok(())
+    }
+
+    /// Registers the input device with the kernel input core.
+    ///
+    /// Consumes the `AllocatedDevice` and returns a [`RegisteredDevice`].
+    #[inline]
+    pub fn register(mut self) -> Result<RegisteredDevice> {
+        // SAFETY: `ptr` is valid and was allocated by `input_allocate_device`.
+        to_result(unsafe { bindings::input_register_device(self.ptr.as_ptr()) })?;
+
+        // SAFETY: `device_add` during `input_register_device` acquires its own reference
+        // to `parent`, so we drop our pre-registration reference to avoid a leak.
+        unsafe {
+            let parent = (*self.ptr.as_ptr()).dev.parent;
+            if !parent.is_null() {
+                bindings::put_device(parent);
+            }
+        }
+
+        let ptr = self.ptr;
+        let phys = self.phys.take();
+        core::mem::forget(self);
+
+        Ok(RegisteredDevice { ptr, _phys: phys })
+    }
+}
+
+impl Drop for AllocatedDevice {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: `self.ptr` was allocated by `input_allocate_device` and has not been registered.
+        unsafe {
+            let parent = (*self.ptr.as_ptr()).dev.parent;
+            if !parent.is_null() {
+                bindings::put_device(parent);
+            }
+            bindings::input_free_device(self.ptr.as_ptr());
+        }
+    }
+}
+
+// SAFETY: `AllocatedDevice` exclusively owns its `input_dev` pointer and can be transferred
+// across threads.
+unsafe impl Send for AllocatedDevice {}
+// SAFETY: `AllocatedDevice` has exclusive ownership and thread-safe methods.
+unsafe impl Sync for AllocatedDevice {}
+
+/// A registered input device capable of reporting events to userspace.
+pub struct RegisteredDevice {
+    ptr: NonNull<bindings::input_dev>,
+    _phys: Option<KBox<[u8; 64]>>,
+}
+
+impl RegisteredDevice {
+    /// Reports a binary button or key state event.
+    #[inline]
+    pub fn report_key(&self, code: u32, value: bool) {
+        // SAFETY: `self.ptr` is valid and registered with the input core.
+        unsafe {
+            bindings::input_report_key(self.ptr.as_ptr(), code, if value { 1 } else { 0 });
+        }
+    }
+
+    /// Reports an absolute axis position value.
+    #[inline]
+    pub fn report_abs(&self, code: u32, value: i32) {
+        // SAFETY: `self.ptr` is valid and registered with the input core.
+        unsafe {
+            bindings::input_report_abs(self.ptr.as_ptr(), code, value);
+        }
+    }
+
+    /// Flushes and synchronizes all reported events into a single input packet.
+    #[inline]
+    pub fn sync(&self) {
+        // SAFETY: `self.ptr` is valid and registered with the input core.
+        unsafe {
+            bindings::input_sync(self.ptr.as_ptr());
+        }
+    }
+}
+
+impl Drop for RegisteredDevice {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: `self.ptr` was successfully registered with `input_register_device`.
+        // Unregistering automatically unbinds and frees the device.
+        unsafe {
+            bindings::input_unregister_device(self.ptr.as_ptr());
+        }
+    }
+}
+
+// SAFETY: `RegisteredDevice` can be safely transferred across threads.
+unsafe impl Send for RegisteredDevice {}
+// SAFETY: Event reporting on `input_dev` is thread-safe (protected by internal locks in the
+// input core).
+unsafe impl Sync for RegisteredDevice {}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 1ab41129d557..ff5c978758d0 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -88,6 +88,8 @@
 #[doc(hidden)]
 pub mod impl_flags;
 pub mod init;
+#[cfg(CONFIG_INPUT = "y")]
+pub mod input;
 pub mod interop;
 pub mod interrupt;
 pub mod io;
-- 
2.56.0