1 files changed, 199 insertions, 0 deletions
diff --git a/rust/kernel/sysctl.rs b/rust/kernel/sysctl.rs
new file mode 100644
index 000000000000..8f742d60037d
--- /dev/null
+++ b/rust/kernel/sysctl.rs
@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! System control.
+//!
+//! C header: [`include/linux/sysctl.h`](../../../../include/linux/sysctl.h)
+//!
+//! Reference: <https://www.kernel.org/doc/Documentation/sysctl/README>
+
+use alloc::boxed::Box;
+use alloc::vec::Vec;
+use core::mem;
+use core::ptr;
+use core::sync::atomic;
+
+use crate::{
+    bindings,
+    error::code::*,
+    io_buffer::IoBufferWriter,
+    str::CStr,
+    types,
+    user_ptr::{UserSlicePtr, UserSlicePtrWriter},
+    Result,
+};
+
+/// Sysctl storage.
+pub trait SysctlStorage: Sync {
+    /// Writes a byte slice.
+    fn store_value(&self, data: &[u8]) -> (usize, Result);
+
+    /// Reads via a [`UserSlicePtrWriter`].
+    fn read_value(&self, data: &mut UserSlicePtrWriter) -> (usize, Result);
+}
+
+fn trim_whitespace(mut data: &[u8]) -> &[u8] {
+    while !data.is_empty() && (data[0] == b' ' || data[0] == b'\t' || data[0] == b'\n') {
+        data = &data[1..];
+    }
+    while !data.is_empty()
+        && (data[data.len() - 1] == b' '
+            || data[data.len() - 1] == b'\t'
+            || data[data.len() - 1] == b'\n')
+    {
+        data = &data[..data.len() - 1];
+    }
+    data
+}
+
+impl<T> SysctlStorage for &T
+where
+    T: SysctlStorage,
+{
+    fn store_value(&self, data: &[u8]) -> (usize, Result) {
+        (*self).store_value(data)
+    }
+
+    fn read_value(&self, data: &mut UserSlicePtrWriter) -> (usize, Result) {
+        (*self).read_value(data)
+    }
+}
+
+impl SysctlStorage for atomic::AtomicBool {
+    fn store_value(&self, data: &[u8]) -> (usize, Result) {
+        let result = match trim_whitespace(data) {
+            b"0" => {
+                self.store(false, atomic::Ordering::Relaxed);
+                Ok(())
+            }
+            b"1" => {
+                self.store(true, atomic::Ordering::Relaxed);
+                Ok(())
+            }
+            _ => Err(EINVAL),
+        };
+        (data.len(), result)
+    }
+
+    fn read_value(&self, data: &mut UserSlicePtrWriter) -> (usize, Result) {
+        let value = if self.load(atomic::Ordering::Relaxed) {
+            b"1\n"
+        } else {
+            b"0\n"
+        };
+        (value.len(), data.write_slice(value))
+    }
+}
+
+/// Holds a single `sysctl` entry (and its table).
+pub struct Sysctl<T: SysctlStorage> {
+    inner: Box<T>,
+    // Responsible for keeping the `ctl_table` alive.
+    _table: Box<[bindings::ctl_table]>,
+    header: *mut bindings::ctl_table_header,
+}
+
+// SAFETY: The only public method we have is `get()`, which returns `&T`, and
+// `T: Sync`. Any new methods must adhere to this requirement.
+unsafe impl<T: SysctlStorage> Sync for Sysctl<T> {}
+
+unsafe extern "C" fn proc_handler<T: SysctlStorage>(
+    ctl: *mut bindings::ctl_table,
+    write: core::ffi::c_int,
+    buffer: *mut core::ffi::c_void,
+    len: *mut usize,
+    ppos: *mut bindings::loff_t,
+) -> core::ffi::c_int {
+    // If we are reading from some offset other than the beginning of the file,
+    // return an empty read to signal EOF.
+    if unsafe { *ppos } != 0 && write == 0 {
+        unsafe { *len = 0 };
+        return 0;
+    }
+
+    let data = unsafe { UserSlicePtr::new(buffer, *len) };
+    let storage = unsafe { &*((*ctl).data as *const T) };
+    let (bytes_processed, result) = if write != 0 {
+        let data = match data.read_all() {
+            Ok(r) => r,
+            Err(e) => return e.to_kernel_errno(),
+        };
+        storage.store_value(&data)
+    } else {
+        let mut writer = data.writer();
+        storage.read_value(&mut writer)
+    };
+    unsafe { *len = bytes_processed };
+    unsafe { *ppos += *len as bindings::loff_t };
+    match result {
+        Ok(()) => 0,
+        Err(e) => e.to_kernel_errno(),
+    }
+}
+
+impl<T: SysctlStorage> Sysctl<T> {
+    /// Registers a single entry in `sysctl`.
+    pub fn register(
+        path: &'static CStr,
+        name: &'static CStr,
+        storage: T,
+        mode: types::Mode,
+    ) -> Result<Sysctl<T>> {
+        if name.contains(&b'/') {
+            return Err(EINVAL);
+        }
+
+        let storage = Box::try_new(storage)?;
+        let mut table = Vec::try_with_capacity(2)?;
+        table.try_push(bindings::ctl_table {
+            procname: name.as_char_ptr(),
+            mode: mode.as_int(),
+            data: &*storage as *const T as *mut core::ffi::c_void,
+            proc_handler: Some(proc_handler::<T>),
+
+            maxlen: 0,
+            child: ptr::null_mut(),
+            poll: ptr::null_mut(),
+            extra1: ptr::null_mut(),
+            extra2: ptr::null_mut(),
+        })?;
+        table.try_push(unsafe { mem::zeroed() })?;
+        let mut table = table.try_into_boxed_slice()?;
+
+        let result = unsafe { bindings::register_sysctl(path.as_char_ptr(), table.as_mut_ptr()) };
+        if result.is_null() {
+            return Err(ENOMEM);
+        }
+
+        Ok(Sysctl {
+            inner: storage,
+            _table: table,
+            header: result,
+        })
+    }
+
+    /// Gets the storage.
+    pub fn get(&self) -> &T {
+        &self.inner
+    }
+}
+
+impl<T: SysctlStorage> Drop for Sysctl<T> {
+    fn drop(&mut self) {
+        unsafe {
+            bindings::unregister_sysctl_table(self.header);
+        }
+        self.header = ptr::null_mut();
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_trim_whitespace() {
+        assert_eq!(trim_whitespace(b"foo    "), b"foo");
+        assert_eq!(trim_whitespace(b"    foo"), b"foo");
+        assert_eq!(trim_whitespace(b"  foo  "), b"foo");
+    }
+}