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a=openpgp-sha256; l=8482; i=aliceryhl@google.com; h=from:subject:message-id; bh=rtZ/Cz0nmdTIH2ZRYlFWyz7pI2Orl32ZaW2okmlCPYA=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBmsiw5GcWX+66OuYPUTv78Aag/LHFwoDBvQ58sO qO4duJRgPOJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZrIsOQAKCRAEWL7uWMY5 Rn7/D/48VM+WdeuVsx+cTPqhRwnpbdew/l3fa+6gNcqpNQScWs9H9Dkvi+f99caoq+tNaWXiHDD GOzoXd8ZqabQk5P98nEBwapAeRs+/1fzJHroBb7RtmfkJRsIiZhNpB6eVdkmrOiAVt8RRGc0/3x 3QRZrLOZVGJRokoBzUHmO3KbNpze5MJMQAl4BQMJof5ReFA/JmOkbjuz+04f/t/sqoRv6iwbBTr 937Hww9DNztnOKZlfEk07qMQhaEOrXpigAwIsOoc2VaZWZkE5aDo9ySZ3czGlE7iyCbDqCyt1G2 b0lGJ1wE9FxtPxhRirn3wo1EwQsvzlvTofP05ysEVHftVqk5jiufJObUVzLTy3r/6LfvIQI5o11 2LcLWzOi7960pP+7+Jg+zmOd9TBjDRVyztvPBG3+RYsi+yQBBrudd61AaIJvo1iaiZrq99QyTye FahV+AP6i+THdCPsc1vH4zl/mTMgx3cu2KMHkZ5/p0nHQaK+jF5PAEiE9PJOq57pJ/onCUTWg02 LoLVB/PLe7USLZ12dCYw5EszmWv3aYQ2mTBGoZx3Sw/7Ld1VJZYH0H6i1YltTEY+fqNVVLox6Mo QdKVnXAn1Eb6e785ROQeIzo9QDpZ2r4Uos1RyoQY+aw2Zu3Ve+iR/YrfB9aB4g99zs27PlG3xHM JVJkLK0lzzZBmZQ== X-Mailer: b4 0.13.0 Message-ID: <20240806-linked-list-v4-5-23efc510ec92@google.com> Subject: [PATCH v4 05/10] rust: list: add macro for implementing ListItem From: Alice Ryhl To: Miguel Ojeda , Andrew Morton Cc: Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Marco Elver , Coly Li , Paolo Abeni , Pierre Gondois , Ingo Molnar , Jakub Kicinski , Wei Yang , Matthew Wilcox , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Alice Ryhl , Kees Cook Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Alice Ryhl --- rust/kernel/list.rs | 3 + rust/kernel/list/impl_list_item_mod.rs | 143 +++++++++++++++++++++++++++++++++ 2 files changed, 146 insertions(+) diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs index 074ae863ff5a..670d53989b8f 100644 --- a/rust/kernel/list.rs +++ b/rust/kernel/list.rs @@ -8,6 +8,9 @@ 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}; diff --git a/rust/kernel/list/impl_list_item_mod.rs b/rust/kernel/list/impl_list_item_mod.rs new file mode 100644 index 000000000000..30886e64b8ef --- /dev/null +++ b/rust/kernel/list/impl_list_item_mod.rs @@ -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` 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` field at the given offset. +/// +/// The implementation of `raw_get_list_links` must not be changed. +pub unsafe trait HasListLinks { + /// The offset of the `ListLinks` field. + const OFFSET: usize; + + /// Returns a pointer to the [`ListLinks`] field. + /// + /// # Safety + /// + /// The provided pointer must point at a valid struct of type `Self`. + /// + /// [`ListLinks`]: 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 { + // 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 } + } +} + +/// 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 implementation 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 { + >::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 = >::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 { >::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 = >::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; -- 2.46.0.rc2.264.g509ed76dc8-goog