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275ad5e793
`ListLinks` does not take a `T` generic parameter, unlike
`ListLinksSelfPtr`.
Thus fix it, which makes it also consistent with the rest of the links
in the file.
Fixes: 40c5329459 ("rust: list: add macro for implementing ListItem")
Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250719232500.822313-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
351 lines
15 KiB
Rust
351 lines
15 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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// Copyright (C) 2024 Google LLC.
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//! Helpers for implementing list traits safely.
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/// Declares that this type has a [`ListLinks<ID>`] field.
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///
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/// This trait is only used to help implement [`ListItem`] safely. If [`ListItem`] is implemented
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/// manually, then this trait is not needed. Use the [`impl_has_list_links!`] macro to implement
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/// this trait.
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///
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/// # Safety
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///
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/// The methods on this trait must have exactly the behavior that the definitions given below have.
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///
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/// [`ListLinks<ID>`]: crate::list::ListLinks
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/// [`ListItem`]: crate::list::ListItem
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pub unsafe trait HasListLinks<const ID: u64 = 0> {
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/// Returns a pointer to the [`ListLinks<ID>`] field.
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///
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/// # Safety
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///
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/// The provided pointer must point at a valid struct of type `Self`.
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///
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/// [`ListLinks<ID>`]: crate::list::ListLinks
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unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut crate::list::ListLinks<ID>;
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}
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/// Implements the [`HasListLinks`] trait for the given type.
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#[macro_export]
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macro_rules! impl_has_list_links {
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($(impl$({$($generics:tt)*})?
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HasListLinks$(<$id:tt>)?
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for $self:ty
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{ self$(.$field:ident)* }
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)*) => {$(
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// SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the
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// right type.
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unsafe impl$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self {
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#[inline]
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unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$id>)? {
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// Statically ensure that `$(.field)*` doesn't follow any pointers.
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//
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// Cannot be `const` because `$self` may contain generics and E0401 says constants
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// "can't use {`Self`,generic parameters} from outer item".
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if false { let _: usize = ::core::mem::offset_of!(Self, $($field).*); }
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// SAFETY: The caller promises that the pointer is not dangling. We know that this
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// expression doesn't follow any pointers, as the `offset_of!` invocation above
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// would otherwise not compile.
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unsafe { ::core::ptr::addr_of_mut!((*ptr)$(.$field)*) }
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}
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}
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)*};
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}
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pub use impl_has_list_links;
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/// Declares that the [`ListLinks<ID>`] field in this struct is inside a
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/// [`ListLinksSelfPtr<T, ID>`].
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///
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/// # Safety
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///
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/// The [`ListLinks<ID>`] field of this struct at [`HasListLinks<ID>::raw_get_list_links`] must be
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/// inside a [`ListLinksSelfPtr<T, ID>`].
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///
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/// [`ListLinks<ID>`]: crate::list::ListLinks
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/// [`ListLinksSelfPtr<T, ID>`]: crate::list::ListLinksSelfPtr
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pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0>
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where
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Self: HasListLinks<ID>,
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{
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}
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/// Implements the [`HasListLinks`] and [`HasSelfPtr`] traits for the given type.
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#[macro_export]
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macro_rules! impl_has_list_links_self_ptr {
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($(impl$({$($generics:tt)*})?
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HasSelfPtr<$item_type:ty $(, $id:tt)?>
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for $self:ty
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{ self$(.$field:ident)* }
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)*) => {$(
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// SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the
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// right type.
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unsafe impl$(<$($generics)*>)? $crate::list::HasSelfPtr<$item_type $(, $id)?> for $self {}
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unsafe impl$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self {
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#[inline]
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unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$id>)? {
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// SAFETY: The caller promises that the pointer is not dangling.
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let ptr: *mut $crate::list::ListLinksSelfPtr<$item_type $(, $id)?> =
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unsafe { ::core::ptr::addr_of_mut!((*ptr)$(.$field)*) };
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ptr.cast()
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}
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}
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)*};
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}
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pub use impl_has_list_links_self_ptr;
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/// Implements the [`ListItem`] trait for the given type.
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///
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/// Requires that the type implements [`HasListLinks`]. Use the [`impl_has_list_links!`] macro to
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/// implement that trait.
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///
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/// [`ListItem`]: crate::list::ListItem
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///
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/// # Examples
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///
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/// ```
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/// #[pin_data]
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/// struct SimpleListItem {
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/// value: u32,
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/// #[pin]
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/// links: kernel::list::ListLinks,
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/// }
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///
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/// kernel::list::impl_list_arc_safe! {
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/// impl ListArcSafe<0> for SimpleListItem { untracked; }
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/// }
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///
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/// kernel::list::impl_list_item! {
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/// impl ListItem<0> for SimpleListItem { using ListLinks { self.links }; }
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/// }
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///
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/// struct ListLinksHolder {
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/// inner: kernel::list::ListLinks,
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/// }
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///
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/// #[pin_data]
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/// struct ComplexListItem<T, U> {
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/// value: Result<T, U>,
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/// #[pin]
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/// links: ListLinksHolder,
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/// }
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///
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/// kernel::list::impl_list_arc_safe! {
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/// impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; }
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/// }
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///
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/// kernel::list::impl_list_item! {
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/// impl{T, U} ListItem<0> for ComplexListItem<T, U> { using ListLinks { self.links.inner }; }
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/// }
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/// ```
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///
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/// ```
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/// #[pin_data]
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/// struct SimpleListItem {
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/// value: u32,
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/// #[pin]
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/// links: kernel::list::ListLinksSelfPtr<SimpleListItem>,
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/// }
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///
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/// kernel::list::impl_list_arc_safe! {
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/// impl ListArcSafe<0> for SimpleListItem { untracked; }
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/// }
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///
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/// kernel::list::impl_list_item! {
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/// impl ListItem<0> for SimpleListItem { using ListLinksSelfPtr { self.links }; }
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/// }
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///
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/// struct ListLinksSelfPtrHolder<T, U> {
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/// inner: kernel::list::ListLinksSelfPtr<ComplexListItem<T, U>>,
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/// }
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///
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/// #[pin_data]
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/// struct ComplexListItem<T, U> {
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/// value: Result<T, U>,
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/// #[pin]
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/// links: ListLinksSelfPtrHolder<T, U>,
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/// }
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///
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/// kernel::list::impl_list_arc_safe! {
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/// impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; }
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/// }
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///
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/// kernel::list::impl_list_item! {
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/// impl{T, U} ListItem<0> for ComplexListItem<T, U> {
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/// using ListLinksSelfPtr { self.links.inner };
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/// }
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/// }
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/// ```
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#[macro_export]
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macro_rules! impl_list_item {
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(
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$(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty {
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using ListLinks { self$(.$field:ident)* };
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})*
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) => {$(
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$crate::list::impl_has_list_links! {
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impl$({$($generics)*})? HasListLinks<$num> for $self { self$(.$field)* }
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}
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// SAFETY: See GUARANTEES comment on each method.
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unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self {
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// GUARANTEES:
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// * This returns the same pointer as `prepare_to_insert` because `prepare_to_insert`
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// is implemented in terms of `view_links`.
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// * By the type invariants of `ListLinks`, the `ListLinks` has two null pointers when
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// this value is not in a list.
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unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
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// SAFETY: The caller guarantees that `me` points at a valid value of type `Self`.
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unsafe {
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<Self as $crate::list::HasListLinks<$num>>::raw_get_list_links(me.cast_mut())
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}
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}
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// GUARANTEES:
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// * `me` originates from the most recent call to `prepare_to_insert`, which calls
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// `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`.
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// This method uses `container_of` to perform the inverse operation, so it returns the
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// pointer originally passed to `prepare_to_insert`.
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// * The pointer remains valid until the next call to `post_remove` because the caller
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// of the most recent call to `prepare_to_insert` promised to retain ownership of the
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// `ListArc` containing `Self` until the next call to `post_remove`. The value cannot
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// be destroyed while a `ListArc` reference exists.
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unsafe fn view_value(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
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// SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it
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// points at the field `$field` in a value of type `Self`. Thus, reversing that
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// operation is still in-bounds of the allocation.
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$crate::container_of!(me, Self, $($field).*)
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}
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// GUARANTEES:
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// This implementation of `ListItem` will not give out exclusive access to the same
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// `ListLinks` several times because calls to `prepare_to_insert` and `post_remove`
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// must alternate and exclusive access is given up when `post_remove` is called.
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//
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// Other invocations of `impl_list_item!` also cannot give out exclusive access to the
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// same `ListLinks` because you can only implement `ListItem` once for each value of
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// `ID`, and the `ListLinks` fields only work with the specified `ID`.
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unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
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// SAFETY: The caller promises that `me` points at a valid value.
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unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) }
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}
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// GUARANTEES:
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// * `me` originates from the most recent call to `prepare_to_insert`, which calls
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// `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`.
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// This method uses `container_of` to perform the inverse operation, so it returns the
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// pointer originally passed to `prepare_to_insert`.
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unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
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// SAFETY: `me` originates from the most recent call to `prepare_to_insert`, so it
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// points at the field `$field` in a value of type `Self`. Thus, reversing that
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// operation is still in-bounds of the allocation.
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$crate::container_of!(me, Self, $($field).*)
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}
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}
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)*};
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(
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$(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty {
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using ListLinksSelfPtr { self$(.$field:ident)* };
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})*
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) => {$(
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$crate::list::impl_has_list_links_self_ptr! {
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impl$({$($generics)*})? HasSelfPtr<$self> for $self { self$(.$field)* }
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}
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// SAFETY: See GUARANTEES comment on each method.
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unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self {
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// GUARANTEES:
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// This implementation of `ListItem` will not give out exclusive access to the same
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// `ListLinks` several times because calls to `prepare_to_insert` and `post_remove`
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// must alternate and exclusive access is given up when `post_remove` is called.
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//
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// Other invocations of `impl_list_item!` also cannot give out exclusive access to the
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// same `ListLinks` because you can only implement `ListItem` once for each value of
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// `ID`, and the `ListLinks` fields only work with the specified `ID`.
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unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
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// SAFETY: The caller promises that `me` points at a valid value of type `Self`.
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let links_field = unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) };
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let container = $crate::container_of!(
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links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner
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);
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// SAFETY: By the same reasoning above, `links_field` is a valid pointer.
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let self_ptr = unsafe {
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$crate::list::ListLinksSelfPtr::raw_get_self_ptr(container)
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};
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let cell_inner = $crate::types::Opaque::cast_into(self_ptr);
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// SAFETY: This value is not accessed in any other places than `prepare_to_insert`,
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// `post_remove`, or `view_value`. By the safety requirements of those methods,
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// none of these three methods may be called in parallel with this call to
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// `prepare_to_insert`, so this write will not race with any other access to the
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// value.
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unsafe { ::core::ptr::write(cell_inner, me) };
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links_field
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}
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// GUARANTEES:
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// * This returns the same pointer as `prepare_to_insert` because `prepare_to_insert`
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// returns the return value of `view_links`.
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// * By the type invariants of `ListLinks`, the `ListLinks` has two null pointers when
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// this value is not in a list.
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unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
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// SAFETY: The caller promises that `me` points at a valid value of type `Self`.
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unsafe {
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<Self as $crate::list::HasListLinks<$num>>::raw_get_list_links(me.cast_mut())
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}
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}
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// This function is also used as the implementation of `post_remove`, so the caller
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// may choose to satisfy the safety requirements of `post_remove` instead of the safety
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// requirements for `view_value`.
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//
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// GUARANTEES: (always)
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// * This returns the same pointer as the one passed to the most recent call to
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// `prepare_to_insert` since that call wrote that pointer to this location. The value
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// is only modified in `prepare_to_insert`, so it has not been modified since the
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// most recent call.
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//
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// GUARANTEES: (only when using the `view_value` safety requirements)
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// * The pointer remains valid until the next call to `post_remove` because the caller
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// of the most recent call to `prepare_to_insert` promised to retain ownership of the
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// `ListArc` containing `Self` until the next call to `post_remove`. The value cannot
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// be destroyed while a `ListArc` reference exists.
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unsafe fn view_value(links_field: *mut $crate::list::ListLinks<$num>) -> *const Self {
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let container = $crate::container_of!(
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links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner
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);
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// SAFETY: By the same reasoning above, `links_field` is a valid pointer.
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let self_ptr = unsafe {
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$crate::list::ListLinksSelfPtr::raw_get_self_ptr(container)
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};
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let cell_inner = $crate::types::Opaque::cast_into(self_ptr);
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// SAFETY: This is not a data race, because the only function that writes to this
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// value is `prepare_to_insert`, but by the safety requirements the
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// `prepare_to_insert` method may not be called in parallel with `view_value` or
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// `post_remove`.
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unsafe { ::core::ptr::read(cell_inner) }
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}
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// GUARANTEES:
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// The first guarantee of `view_value` is exactly what `post_remove` guarantees.
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unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
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// SAFETY: This specific implementation of `view_value` allows the caller to
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// promise the safety requirements of `post_remove` instead of the safety
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// requirements for `view_value`.
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unsafe { <Self as $crate::list::ListItem<$num>>::view_value(me) }
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}
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}
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)*};
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}
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pub use impl_list_item;
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