From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 5116C428485 for ; Thu, 26 Feb 2026 16:24:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123061; cv=none; b=a6g1YPeYtxjS2syfhplfuxJOU7fouYy4joI99OwGW/6Xbg4Z5eRZ4E/5PHqaE3NtsCi8DvABqp2YDHRpmZOyykGvx01FgtCaYJgQm5PtYNEYLQTEFXvACkMLFhxJ0oFBgSxa2IrdTkWgaW59PfK8oBZlSTWAEuCNaeIUPH8q1fM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772123061; c=relaxed/simple; bh=aGBN3QMumZqCCefJQZL3xlNq8KIeye7wNg65TOT2W7I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bLqD6jPmeRm40iut3WdhfKJENb/0vJbodMqrVncEG+KB1c4s5sOiQAFBbI2SMRG2yhWlw942eCsqEo949zHyvzsbMcb90quT4pfOn5Z7N9iHd6aZXxniLaXS0UVpzEjz04D0OuKGU4yBWwYaDNVW90LsHUmNLm0ZrPrskn9drVM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=XNfvb3gN; arc=none smtp.client-ip=91.218.175.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="XNfvb3gN" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772123046; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Mot2vauLG07vA2kiO70W8m+1wIvRmpWaKTQPNgejD+E=; b=XNfvb3gNCQYVnDPdOX4cgYnYDectI0KeFSjLMjAl64DNssi19dgYuSfMaP8KG4MPGM70wI /Cx/++mtEKJjl6Y2E3LIwM9cmNehjx7aaUd4aRIKFIWg07iwAv94BE11CxqyfubAdNrr99 8/PNQg9ZeCjOyYa8jk8uPVP302WIxBA= Date: Fri, 27 Feb 2026 00:23:34 +0800 Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v11 2/2] rust: clist: Add support to interface with C linked lists To: Joel Fernandes , linux-kernel@vger.kernel.org Cc: Miguel Ojeda , Boqun Feng , Gary Guo , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Alex Gaynor , Danilo Krummrich , Dave Airlie , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter , Daniel Almeida , Koen Koning , Nikola Djukic , Alexandre Courbot , Philipp Stanner , Elle Rhumsaa , Jonathan Corbet , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Huang Rui , Matthew Auld , Matthew Brost , Lucas De Marchi , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Helge Deller , John Hubbard , Alistair Popple , Timur Tabi , Edwin Peer , Andrea Righi , Andy Ritger , Zhi Wang , Balbir Singh , alexeyi@nvidia.com, Eliot Courtney , dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, rust-for-linux@vger.kernel.org, linux-doc@vger.kernel.org, amd-gfx@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-fbdev@vger.kernel.org References: <20260224222734.3153931-1-joelagnelf@nvidia.com> <20260224222734.3153931-3-joelagnelf@nvidia.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Alvin Sun In-Reply-To: <20260224222734.3153931-3-joelagnelf@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2/25/26 06:27, Joel Fernandes wrote: > 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. > > Cc: Nikola Djukic > Reviewed-by: Daniel Almeida > Acked-by: Gary Guo > Signed-off-by: Joel Fernandes > --- > MAINTAINERS | 8 + > rust/helpers/helpers.c | 1 + > rust/helpers/list.c | 17 ++ > rust/kernel/ffi/clist.rs | 338 +++++++++++++++++++++++++++++++++++++++ > rust/kernel/ffi/mod.rs | 2 + > rust/kernel/lib.rs | 1 + > 6 files changed, 367 insertions(+) > create mode 100644 rust/helpers/list.c > create mode 100644 rust/kernel/ffi/clist.rs > > diff --git a/MAINTAINERS b/MAINTAINERS > index dc82a6bd1a61..0dc318c94c99 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -23181,6 +23181,14 @@ T: git https://github.com/Rust-for-Linux/linux.git alloc-next > F: rust/kernel/alloc.rs > F: rust/kernel/alloc/ > > +RUST [FFI HELPER] > +M: Joel Fernandes (CLIST) > +M: Alexandre Courbot (CLIST) > +L: rust-for-linux@vger.kernel.org > +S: Maintained > +T: git https://github.com/Rust-for-Linux/linux.git ffi-next > +F: rust/kernel/ffi/ > + > RUST [NUM] > M: Alexandre Courbot > R: Yury Norov > 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..18095a5593c5 > --- /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 > + > +__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/ffi/clist.rs b/rust/kernel/ffi/clist.rs > new file mode 100644 > index 000000000000..a645358eee58 > --- /dev/null > +++ b/rust/kernel/ffi/clist.rs > @@ -0,0 +1,338 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! FFI interface for C doubly circular intrusive linked lists. > +//! > +//! This module provides Rust abstractions for iterating over C `list_head`-based > +//! linked lists. It should only be used for cases where C and Rust code share > +//! direct access to the same linked list through an FFI interface. > +//! > +//! Note: This *must not* be used by Rust components that just need a linked list > +//! primitive. Use [`kernel::list::List`] instead. > +//! > +//! # 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::::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::::uninit(), > +//! # MaybeUninit::::uninit(), > +//! # MaybeUninit::::uninit(), > +//! # ]; > +//! # > +//! # for (i, item) in items.iter_mut().enumerate() { > +//! # let ptr = item.as_mut_ptr(); > +//! # // SAFETY: `ptr` points to a valid `MaybeUninit`. > +//! # unsafe { (*ptr).value = i as i32 * 10 }; > +//! # // SAFETY: `&raw mut` creates a pointer valid for `INIT_LIST_HEAD`. > +//! # unsafe { bindings::INIT_LIST_HEAD(&raw mut (*ptr).link) }; > +//! # // SAFETY: `link` was just initialized and `head` is a valid list head. > +//! # unsafe { 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); > +//! > +//! 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 and initialized, items are `SampleItemC` with > +//! // embedded `link` field, and `Item` is `#[repr(transparent)]` over `SampleItemC`. > +//! let list = clist_create!(unsafe { 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, // > +}; > + > +/// FFI wrapper for a C `list_head` object used in intrusive linked lists. > +/// > +/// # Invariants > +/// > +/// - The underlying `list_head` has been initialized (e.g. via `INIT_LIST_HEAD()`) and its > +/// `next`/`prev` pointers are valid and non-NULL. > +#[pin_data] > +#[repr(transparent)] > +pub struct CListHead { > + #[pin] > + inner: Opaque, > +} > + > +impl CListHead { > + /// Create a `&CListHead` reference from a raw `list_head` pointer. > + /// > + /// # Safety > + /// > + /// - `ptr` must be a valid pointer to an initialized `list_head` (e.g. via > + /// `INIT_LIST_HEAD()`), with valid non-NULL `next`/`prev` pointers. > + /// - `ptr` must remain valid for the lifetime `'a`. > + /// - The list and all linked `list_head` nodes must not be modified from > + /// anywhere for the lifetime `'a`, unless done so via any [`CListHead`] APIs. > + #[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 and initialized per type invariants. > + // - The `next` pointer is valid and non-NULL per type invariants > + // (initialized via `INIT_LIST_HEAD()` or equivalent). > + 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 { > + 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: `list_head` contains no thread-bound state; it only holds > +// `next`/`prev` pointers. > +unsafe impl Send for CListHead {} > + > +// SAFETY: `CListHead` can be shared among threads as modifications are > +// not allowed at the moment. > +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 initialized and valid list. > +struct CListHeadIter<'a> { Hi, Joel Thanks for the clist abstraction. The Tyr debugfs [1] I'm implementing needs to iterate over a GpuVm's VA list, and I'd like to switch that to a CList-based implementation. Could you make CListHeadIter public and expose a public constructor? Or do you have a better suggestion? The VA list mixes two node types in one list — GpuVa (with driver-specific data) and KernelGpuVa — so we have to filter/skip nodes and can't use CList as-is. With a public CListHeadIter and new(), we can implement a custom iterator (like our current GpuVaIter) on top of CListHeadIter and then migrate that code to clist instead of hand-rolled list traversal. [1] https://gitlab.freedesktop.org/panfrost/linux/-/merge_requests/59/diffs?commit_id=0853a7b69a42b32832c8e57da63272a8585cb76b#23581e10c8b583e85ebde61a1675ac3a70e37c14_84_148 Thanks, Alvin Sun > + /// 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 { > + // 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 intended for FFI use-cases where > +/// C subsystem manages a linked list that Rust code needs to read. Generally > +/// required only for special cases. > +/// > +/// A sentinel head [`CListHead`] 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 sentinel [`CListHead`] has been initialized (e.g. via `INIT_LIST_HEAD()`) with valid > +/// non-NULL `next`/`prev` pointers. > +/// - `OFFSET` is the byte offset of the `list_head` field within the struct that `T` wraps. > +/// - All the list's `list_head` nodes have been initialized with valid non-NULL `next`/`prev` > +/// pointers. > +#[repr(transparent)] > +pub struct CList(CListHead, PhantomData); > + > +impl CList { > + /// Create a typed [`CList`] reference from a raw sentinel `list_head` pointer. > + /// > + /// # Safety > + /// > + /// - `ptr` must be a valid pointer to an initialized sentinel `list_head` (e.g. via > + /// `INIT_LIST_HEAD()`), with valid non-NULL `next`/`prev` pointers. > + /// - `ptr` must remain valid for the lifetime `'a`. > + /// - The list and all linked nodes must not be concurrently modified 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; > + > + #[inline] > + fn next(&mut self) -> Option { > + 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::() }) > + } > +} > + > +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` 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`. > +/// - `$field`: The name of the `list_head` field within the C struct. > +/// > +/// # Safety > +/// > +/// The caller must ensure: > +/// > +/// - `$head` is a valid, initialized sentinel `list_head` (e.g. via `INIT_LIST_HEAD()`) > +/// pointing to a list that is not concurrently modified for the lifetime of the `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 { > + (unsafe { $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 $crate::bindings::list_head = > + |p| unsafe { &raw const (*p).$($field).+ }; > + > + // Calculate offset and create `CList`. > + const OFFSET: usize = ::core::mem::offset_of!($c_type, $($field).+); > + // SAFETY: The caller of this macro is responsible for ensuring safety. > + unsafe { $crate::ffi::clist::CList::<$rust_type, OFFSET>::from_raw($head) } > + }}; > +} > diff --git a/rust/kernel/ffi/mod.rs b/rust/kernel/ffi/mod.rs > index 7d844e9cb339..8c235ca0d1e3 100644 > --- a/rust/kernel/ffi/mod.rs > +++ b/rust/kernel/ffi/mod.rs > @@ -5,3 +5,5 @@ > // Re-export C type definitions from the `ffi` crate so that existing > // `kernel::ffi::c_int` etc. paths continue to work. > pub use ::ffi::*; > + > +pub mod clist; > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index 0a77b4c0ffeb..58dbb02c5197 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -28,6 +28,7 @@ > #![feature(lint_reasons)] > // > // Stable since Rust 1.82.0. > +#![feature(offset_of_nested)] > #![feature(raw_ref_op)] > // > // Stable since Rust 1.83.0.