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rust: list: add macro for implementing ListItem

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Adds a macro for safely implementing the ListItem trait. As part of the
implementation of the macro, we also provide a HasListLinks trait
similar to the workqueue's HasWorkItem trait.

The HasListLinks trait is only necessary if you are implementing
ListItem using the impl_list_item macro.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240814-linked-list-v5-5-f5f5e8075da0@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Alice Ryhl 2024-08-14 08:05:24 +00:00 committed by Miguel Ojeda
parent 14176295fe
commit 40c5329459
2 changed files with 146 additions and 0 deletions
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3
rust/kernel/list.rs
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@ -8,6 +8,9 @@ use crate::init::PinInit;
use crate::types::Opaque;
use core::ptr;
mod impl_list_item_mod;
pub use self::impl_list_item_mod::{impl_has_list_links, impl_list_item, HasListLinks};
mod arc;
pub use self::arc::{impl_list_arc_safe, AtomicTracker, ListArc, ListArcSafe, TryNewListArc};

143
rust/kernel/list/impl_list_item_mod.rs Normal file
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@ -0,0 +1,143 @@
// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2024 Google LLC.
//! Helpers for implementing list traits safely.
use crate::list::ListLinks;
/// Declares that this type has a `ListLinks<ID>` field at a fixed offset.
///
/// This trait is only used to help implement `ListItem` safely. If `ListItem` is implemented
/// manually, then this trait is not needed. Use the [`impl_has_list_links!`] macro to implement
/// this trait.
///
/// # Safety
///
/// All values of this type must have a `ListLinks<ID>` field at the given offset.
///
/// The behavior of `raw_get_list_links` must not be changed.
pub unsafe trait HasListLinks<const ID: u64 = 0> {
/// The offset of the `ListLinks` field.
const OFFSET: usize;
/// Returns a pointer to the [`ListLinks<T, ID>`] field.
///
/// # Safety
///
/// The provided pointer must point at a valid struct of type `Self`.
///
/// [`ListLinks<T, ID>`]: ListLinks
// We don't really need this method, but it's necessary for the implementation of
// `impl_has_list_links!` to be correct.
#[inline]
unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut ListLinks<ID> {
// SAFETY: The caller promises that the pointer is valid. The implementer promises that the
// `OFFSET` constant is correct.
unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut ListLinks<ID> }
}
}
/// Implements the [`HasListLinks`] trait for the given type.
#[macro_export]
macro_rules! impl_has_list_links {
($(impl$(<$($implarg:ident),*>)?
HasListLinks$(<$id:tt>)?
for $self:ident $(<$($selfarg:ty),*>)?
{ self$(.$field:ident)* }
)*) => {$(
// SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the
// right type.
//
// The behavior of `raw_get_list_links` is not changed since the `addr_of_mut!` macro is
// equivalent to the pointer offset operation in the trait definition.
unsafe impl$(<$($implarg),*>)? $crate::list::HasListLinks$(<$id>)? for
$self $(<$($selfarg),*>)?
{
const OFFSET: usize = ::core::mem::offset_of!(Self, $($field).*) as usize;
#[inline]
unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$id>)? {
// SAFETY: The caller promises that the pointer is not dangling. We know that this
// expression doesn't follow any pointers, as the `offset_of!` invocation above
// would otherwise not compile.
unsafe { ::core::ptr::addr_of_mut!((*ptr)$(.$field)*) }
}
}
)*};
}
pub use impl_has_list_links;
/// Implements the [`ListItem`] trait for the given type.
///
/// Requires that the type implements [`HasListLinks`]. Use the [`impl_has_list_links!`] macro to
/// implement that trait.
///
/// [`ListItem`]: crate::list::ListItem
#[macro_export]
macro_rules! impl_list_item {
(
$(impl$({$($generics:tt)*})? ListItem<$num:tt> for $t:ty {
using ListLinks;
})*
) => {$(
// SAFETY: See GUARANTEES comment on each method.
unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $t {
// GUARANTEES:
// * This returns the same pointer as `prepare_to_insert` because `prepare_to_insert`
// is implemented in terms of `view_links`.
// * By the type invariants of `ListLinks`, the `ListLinks` has two null pointers when
// this value is not in a list.
unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
// SAFETY: The caller guarantees that `me` points at a valid value of type `Self`.
unsafe {
<Self as $crate::list::HasListLinks<$num>>::raw_get_list_links(me.cast_mut())
}
}
// GUARANTEES:
// * `me` originates from the most recent call to `prepare_to_insert`, which just added
// `offset` to the pointer passed to `prepare_to_insert`. This method subtracts
// `offset` from `me` so it returns the pointer originally passed to
// `prepare_to_insert`.
// * The pointer remains valid until the next call to `post_remove` because the caller
// of the most recent call to `prepare_to_insert` promised to retain ownership of the
// `ListArc` containing `Self` until the next call to `post_remove`. The value cannot
// be destroyed while a `ListArc` reference exists.
unsafe fn view_value(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
let offset = <Self as $crate::list::HasListLinks<$num>>::OFFSET;
// SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it
// points at the field at offset `offset` in a value of type `Self`. Thus,
// subtracting `offset` from `me` is still in-bounds of the allocation.
unsafe { (me as *const u8).sub(offset) as *const Self }
}
// GUARANTEES:
// This implementation of `ListItem` will not give out exclusive access to the same
// `ListLinks` several times because calls to `prepare_to_insert` and `post_remove`
// must alternate and exclusive access is given up when `post_remove` is called.
//
// Other invocations of `impl_list_item!` also cannot give out exclusive access to the
// same `ListLinks` because you can only implement `ListItem` once for each value of
// `ID`, and the `ListLinks` fields only work with the specified `ID`.
unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
// SAFETY: The caller promises that `me` points at a valid value.
unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) }
}
// GUARANTEES:
// * `me` originates from the most recent call to `prepare_to_insert`, which just added
// `offset` to the pointer passed to `prepare_to_insert`. This method subtracts
// `offset` from `me` so it returns the pointer originally passed to
// `prepare_to_insert`.
unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
let offset = <Self as $crate::list::HasListLinks<$num>>::OFFSET;
// SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it
// points at the field at offset `offset` in a value of type `Self`. Thus,
// subtracting `offset` from `me` is still in-bounds of the allocation.
unsafe { (me as *const u8).sub(offset) as *const Self }
}
}
)*};
}
pub use impl_list_item;