Add a new module `clist` for working with C's doubly circular linked lists. Provide low-level iteration over list nodes.
Typed iteration over actual items is provided with a `clist_create` macro to assist in creation of the `CList` type. Acked-by: Gary Guo <[email protected]> Signed-off-by: Joel Fernandes <[email protected]> --- MAINTAINERS | 7 + rust/helpers/helpers.c | 1 + rust/helpers/list.c | 17 +++ rust/kernel/clist.rs | 320 +++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 5 files changed, 346 insertions(+) create mode 100644 rust/helpers/list.c create mode 100644 rust/kernel/clist.rs diff --git a/MAINTAINERS b/MAINTAINERS index 900fc00b73e6..310bb479260c 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -23204,6 +23204,13 @@ S: Maintained T: git https://github.com/Rust-for-Linux/linux.git rust-analyzer-next F: scripts/generate_rust_analyzer.py +RUST TO C LIST INTERFACES +M: Joel Fernandes <[email protected]> +M: Alexandre Courbot <[email protected]> +L: [email protected] +S: Maintained +F: rust/kernel/clist.rs + RXRPC SOCKETS (AF_RXRPC) M: David Howells <[email protected]> M: Marc Dionne <[email protected]> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index a3c42e51f00a..724fcb8240ac 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -35,6 +35,7 @@ #include "io.c" #include "jump_label.c" #include "kunit.c" +#include "list.c" #include "maple_tree.c" #include "mm.c" #include "mutex.c" diff --git a/rust/helpers/list.c b/rust/helpers/list.c new file mode 100644 index 000000000000..4c1f9c111ec8 --- /dev/null +++ b/rust/helpers/list.c @@ -0,0 +1,17 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Helpers for C Circular doubly linked list implementation. + */ + +#include <linux/list.h> + +__rust_helper void rust_helper_INIT_LIST_HEAD(struct list_head *list) +{ + INIT_LIST_HEAD(list); +} + +__rust_helper void rust_helper_list_add_tail(struct list_head *new, struct list_head *head) +{ + list_add_tail(new, head); +} diff --git a/rust/kernel/clist.rs b/rust/kernel/clist.rs new file mode 100644 index 000000000000..8aa72b5d54be --- /dev/null +++ b/rust/kernel/clist.rs @@ -0,0 +1,320 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! A C doubly circular intrusive linked list interface for rust code. +//! +//! # Examples +//! +//! ``` +//! use kernel::{ +//! bindings, +//! clist_create, +//! types::Opaque, // +//! }; +//! # // Create test list with values (0, 10, 20) - normally done by C code but it is +//! # // emulated here for doctests using the C bindings. +//! # use core::mem::MaybeUninit; +//! # +//! # /// C struct with embedded `list_head` (typically will be allocated by C code). +//! # #[repr(C)] +//! # pub struct SampleItemC { +//! # pub value: i32, +//! # pub link: bindings::list_head, +//! # } +//! # +//! # let mut head = MaybeUninit::<bindings::list_head>::uninit(); +//! # +//! # let head = head.as_mut_ptr(); +//! # // SAFETY: head and all the items are test objects allocated in this scope. +//! # unsafe { bindings::INIT_LIST_HEAD(head) }; +//! # +//! # let mut items = [ +//! # MaybeUninit::<SampleItemC>::uninit(), +//! # MaybeUninit::<SampleItemC>::uninit(), +//! # MaybeUninit::<SampleItemC>::uninit(), +//! # ]; +//! # +//! # for (i, item) in items.iter_mut().enumerate() { +//! # let ptr = item.as_mut_ptr(); +//! # // SAFETY: pointers are to allocated test objects with a list_head field. +//! # unsafe { +//! # (*ptr).value = i as i32 * 10; +//! # // &raw mut computes address of link directly as link is uninitialized. +//! # bindings::INIT_LIST_HEAD(&raw mut (*ptr).link); +//! # bindings::list_add_tail(&mut (*ptr).link, head); +//! # } +//! # } +//! +//! // Rust wrapper for the C struct. +//! // The list item struct in this example is defined in C code as: +//! // struct SampleItemC { +//! // int value; +//! // struct list_head link; +//! // }; +//! // +//! #[repr(transparent)] +//! pub struct Item(Opaque<SampleItemC>); +//! +//! impl Item { +//! pub fn value(&self) -> i32 { +//! // SAFETY: [`Item`] has same layout as [`SampleItemC`]. +//! unsafe { (*self.0.get()).value } +//! } +//! } +//! +//! // Create typed [`CList`] from sentinel head. +//! // SAFETY: head is valid, items are [`SampleItemC`] with embedded `link` field. +//! let list = unsafe { clist_create!(head, Item, SampleItemC, link) }; +//! +//! // Iterate directly over typed items. +//! let mut found_0 = false; +//! let mut found_10 = false; +//! let mut found_20 = false; +//! +//! for item in list.iter() { +//! let val = item.value(); +//! if val == 0 { found_0 = true; } +//! if val == 10 { found_10 = true; } +//! if val == 20 { found_20 = true; } +//! } +//! +//! assert!(found_0 && found_10 && found_20); +//! ``` + +use core::{ + iter::FusedIterator, + marker::PhantomData, // +}; + +use crate::{ + bindings, + types::Opaque, // +}; + +use pin_init::{ + pin_data, + pin_init, + PinInit // +}; + +/// Wraps a `list_head` object for use in intrusive linked lists. +/// +/// # Invariants +/// +/// - [`CListHead`] represents an allocated and valid `list_head` structure. +#[pin_data] +#[repr(transparent)] +pub struct CListHead { + #[pin] + inner: Opaque<bindings::list_head>, +} + +impl CListHead { + /// Create a `&CListHead` reference from a raw `list_head` pointer. + /// + /// # Safety + /// + /// - `ptr` must be a valid pointer to an allocated and initialized `list_head` structure. + /// - `ptr` must remain valid and unmodified for the lifetime `'a`. + /// - The list and all linked `list_head` nodes must not be modified by non-Rust code + /// for the lifetime `'a`. + #[inline] + pub unsafe fn from_raw<'a>(ptr: *mut bindings::list_head) -> &'a Self { + // SAFETY: + // - [`CListHead`] has same layout as `list_head`. + // - `ptr` is valid and unmodified for 'a per caller guarantees. + unsafe { &*ptr.cast() } + } + + /// Get the raw `list_head` pointer. + #[inline] + pub fn as_raw(&self) -> *mut bindings::list_head { + self.inner.get() + } + + /// Get the next [`CListHead`] in the list. + #[inline] + pub fn next(&self) -> &Self { + let raw = self.as_raw(); + // SAFETY: + // - `self.as_raw()` is valid per type invariants. + // - The `next` pointer is guaranteed to be non-NULL. + unsafe { Self::from_raw((*raw).next) } + } + + /// Check if this node is linked in a list (not isolated). + #[inline] + pub fn is_linked(&self) -> bool { + let raw = self.as_raw(); + // SAFETY: self.as_raw() is valid per type invariants. + unsafe { (*raw).next != raw && (*raw).prev != raw } + } + + /// Pin-initializer that initializes the list head. + pub fn new() -> impl PinInit<Self> { + pin_init!(Self { + // SAFETY: `INIT_LIST_HEAD` initializes `slot` to a valid empty list. + inner <- Opaque::ffi_init(|slot| unsafe { bindings::INIT_LIST_HEAD(slot) }), + }) + } +} + +// SAFETY: [`CListHead`] can be sent to any thread. +unsafe impl Send for CListHead {} + +// SAFETY: [`CListHead`] can be shared among threads as it is not modified +// by non-Rust code per safety requirements of [`CListHead::from_raw`]. +unsafe impl Sync for CListHead {} + +impl PartialEq for CListHead { + #[inline] + fn eq(&self, other: &Self) -> bool { + core::ptr::eq(self, other) + } +} + +impl Eq for CListHead {} + +/// Low-level iterator over `list_head` nodes. +/// +/// An iterator used to iterate over a C intrusive linked list (`list_head`). Caller has to +/// perform conversion of returned [`CListHead`] to an item (using `container_of` macro or similar). +/// +/// # Invariants +/// +/// [`CListHeadIter`] is iterating over an allocated, initialized and valid list. +struct CListHeadIter<'a> { + /// Current position in the list. + current: &'a CListHead, + /// The sentinel head (used to detect end of iteration). + sentinel: &'a CListHead, +} + +impl<'a> Iterator for CListHeadIter<'a> { + type Item = &'a CListHead; + + #[inline] + fn next(&mut self) -> Option<Self::Item> { + // Check if we've reached the sentinel (end of list). + if self.current == self.sentinel { + return None; + } + + let item = self.current; + self.current = item.next(); + Some(item) + } +} + +impl<'a> FusedIterator for CListHeadIter<'a> {} + +/// A typed C linked list with a sentinel head. +/// +/// A sentinel head represents the entire linked list and can be used for +/// iteration over items of type `T`, it is not associated with a specific item. +/// +/// The const generic `OFFSET` specifies the byte offset of the `list_head` field within +/// the struct that `T` wraps. +/// +/// # Invariants +/// +/// - The [`CListHead`] is an allocated and valid sentinel C `list_head` structure. +/// - `OFFSET` is the byte offset of the `list_head` field within the struct that `T` wraps. +/// - All the list's `list_head` nodes are allocated and have valid next/prev pointers. +#[repr(transparent)] +pub struct CList<T, const OFFSET: usize>(CListHead, PhantomData<T>); + +impl<T, const OFFSET: usize> CList<T, OFFSET> { + /// Create a typed [`CList`] reference from a raw sentinel `list_head` pointer. + /// + /// # Safety + /// + /// - `ptr` must be a valid pointer to an allocated and initialized `list_head` structure + /// representing a list sentinel. + /// - `ptr` must remain valid and unmodified for the lifetime `'a`. + /// - The list must contain items where the `list_head` field is at byte offset `OFFSET`. + /// - `T` must be `#[repr(transparent)]` over the C struct. + #[inline] + pub unsafe fn from_raw<'a>(ptr: *mut bindings::list_head) -> &'a Self { + // SAFETY: + // - [`CList`] has same layout as [`CListHead`] due to repr(transparent). + // - Caller guarantees `ptr` is a valid, sentinel `list_head` object. + unsafe { &*ptr.cast() } + } + + /// Check if the list is empty. + #[inline] + pub fn is_empty(&self) -> bool { + !self.0.is_linked() + } + + /// Create an iterator over typed items. + #[inline] + pub fn iter(&self) -> CListIter<'_, T, OFFSET> { + let head = &self.0; + CListIter { + head_iter: CListHeadIter { + current: head.next(), + sentinel: head, + }, + _phantom: PhantomData, + } + } +} + +/// High-level iterator over typed list items. +pub struct CListIter<'a, T, const OFFSET: usize> { + head_iter: CListHeadIter<'a>, + _phantom: PhantomData<&'a T>, +} + +impl<'a, T, const OFFSET: usize> Iterator for CListIter<'a, T, OFFSET> { + type Item = &'a T; + + fn next(&mut self) -> Option<Self::Item> { + let head = self.head_iter.next()?; + + // Convert to item using OFFSET. + // SAFETY: `item_ptr` calculation from `OFFSET` (calculated using offset_of!) + // is valid per invariants. + Some(unsafe { &*head.as_raw().byte_sub(OFFSET).cast::<T>() }) + } +} + +impl<'a, T, const OFFSET: usize> FusedIterator for CListIter<'a, T, OFFSET> {} + +/// Create a C doubly-circular linked list interface `CList` from a raw `list_head` pointer. +/// +/// This macro creates a `CList<T, OFFSET>` that can iterate over items of type `$rust_type` +/// linked via the `$field` field in the underlying C struct `$c_type`. +/// +/// # Arguments +/// +/// - `$head`: Raw pointer to the sentinel `list_head` object (`*mut bindings::list_head`). +/// - `$rust_type`: Each item's rust wrapper type. +/// - `$c_type`: Each item's C struct type that contains the embedded `list_head`. +/// - `$field`: The name of the `list_head` field within the C struct. +/// +/// # Safety +/// +/// This is an unsafe macro. The caller must ensure: +/// +/// - `$head` is a valid, initialized sentinel `list_head` pointing to a list that remains +/// unmodified for the lifetime of the rust `CList`. +/// - The list contains items of type `$c_type` linked via an embedded `$field`. +/// - `$rust_type` is `#[repr(transparent)]` over `$c_type` or has compatible layout. +/// +/// # Examples +/// +/// Refer to the examples in this module's documentation. +#[macro_export] +macro_rules! clist_create { + ($head:expr, $rust_type:ty, $c_type:ty, $($field:tt).+) => {{ + // Compile-time check that field path is a list_head. + let _: fn(*const $c_type) -> *const $crate::bindings::list_head = + |p| &raw const (*p).$($field).+; + + // Calculate offset and create `CList`. + const OFFSET: usize = ::core::mem::offset_of!($c_type, $($field).+); + $crate::clist::CList::<$rust_type, OFFSET>::from_raw($head) + }}; +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 3da92f18f4ee..fe711d34ca1e 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -75,6 +75,7 @@ pub mod bug; #[doc(hidden)] pub mod build_assert; +pub mod clist; pub mod clk; #[cfg(CONFIG_CONFIGFS_FS)] pub mod configfs; -- 2.34.1
