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| -rw-r--r-- | rust/kernel/list.rs | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs index 8e1533ee987b..074ae863ff5a 100644 --- a/rust/kernel/list.rs +++ b/rust/kernel/list.rs @@ -4,5 +4,124 @@ //! A linked list implementation. +use crate::init::PinInit; +use crate::types::Opaque; +use core::ptr; + mod arc; pub use self::arc::{impl_list_arc_safe, AtomicTracker, ListArc, ListArcSafe, TryNewListArc}; + +/// Implemented by types where a [`ListArc<Self>`] can be inserted into a `List`. +/// +/// # Safety +/// +/// Implementers must ensure that they provide the guarantees documented on methods provided by +/// this trait. +/// +/// [`ListArc<Self>`]: ListArc +pub unsafe trait ListItem<const ID: u64 = 0>: ListArcSafe<ID> { + /// Views the [`ListLinks`] for this value. + /// + /// # Guarantees + /// + /// If there is a previous call to `prepare_to_insert` and there is no call to `post_remove` + /// since the most recent such call, then this returns the same pointer as the one returned by + /// the most recent call to `prepare_to_insert`. + /// + /// Otherwise, the returned pointer points at a read-only [`ListLinks`] with two null pointers. + /// + /// # Safety + /// + /// The provided pointer must point at a valid value. (It need not be in an `Arc`.) + unsafe fn view_links(me: *const Self) -> *mut ListLinks<ID>; + + /// View the full value given its [`ListLinks`] field. + /// + /// Can only be used when the value is in a list. + /// + /// # Guarantees + /// + /// * Returns the same pointer as the one passed to the most recent call to `prepare_to_insert`. + /// * The returned pointer is valid until the next call to `post_remove`. + /// + /// # Safety + /// + /// * The provided pointer must originate from the most recent call to `prepare_to_insert`, or + /// from a call to `view_links` that happened after the most recent call to + /// `prepare_to_insert`. + /// * Since the most recent call to `prepare_to_insert`, the `post_remove` method must not have + /// been called. + unsafe fn view_value(me: *mut ListLinks<ID>) -> *const Self; + + /// This is called when an item is inserted into a `List`. + /// + /// # Guarantees + /// + /// The caller is granted exclusive access to the returned [`ListLinks`] until `post_remove` is + /// called. + /// + /// # Safety + /// + /// * The provided pointer must point at a valid value in an [`Arc`]. + /// * Calls to `prepare_to_insert` and `post_remove` on the same value must alternate. + /// * The caller must own the [`ListArc`] for this value. + /// * The caller must not give up ownership of the [`ListArc`] unless `post_remove` has been + /// called after this call to `prepare_to_insert`. + /// + /// [`Arc`]: crate::sync::Arc + unsafe fn prepare_to_insert(me: *const Self) -> *mut ListLinks<ID>; + + /// This undoes a previous call to `prepare_to_insert`. + /// + /// # Guarantees + /// + /// The returned pointer is the pointer that was originally passed to `prepare_to_insert`. + /// + /// # Safety + /// + /// The provided pointer must be the pointer returned by the most recent call to + /// `prepare_to_insert`. + unsafe fn post_remove(me: *mut ListLinks<ID>) -> *const Self; +} + +#[repr(C)] +#[derive(Copy, Clone)] +struct ListLinksFields { + next: *mut ListLinksFields, + prev: *mut ListLinksFields, +} + +/// The prev/next pointers for an item in a linked list. +/// +/// # Invariants +/// +/// The fields are null if and only if this item is not in a list. +#[repr(transparent)] +pub struct ListLinks<const ID: u64 = 0> { + // This type is `!Unpin` for aliasing reasons as the pointers are part of an intrusive linked + // list. + #[allow(dead_code)] + inner: Opaque<ListLinksFields>, +} + +// SAFETY: The only way to access/modify the pointers inside of `ListLinks<ID>` is via holding the +// associated `ListArc<T, ID>`. Since that type correctly implements `Send`, it is impossible to +// move this an instance of this type to a different thread if the pointees are `!Send`. +unsafe impl<const ID: u64> Send for ListLinks<ID> {} +// SAFETY: The type is opaque so immutable references to a ListLinks are useless. Therefore, it's +// okay to have immutable access to a ListLinks from several threads at once. +unsafe impl<const ID: u64> Sync for ListLinks<ID> {} + +impl<const ID: u64> ListLinks<ID> { + /// Creates a new initializer for this type. + pub fn new() -> impl PinInit<Self> { + // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will + // not be constructed in an `Arc` that already has a `ListArc`. + ListLinks { + inner: Opaque::new(ListLinksFields { + prev: ptr::null_mut(), + next: ptr::null_mut(), + }), + } + } +} |