Commit c77f85b3 authored by Tamir Duberstein's avatar Tamir Duberstein Committed by Miguel Ojeda
Browse files

rust: list: remove OFFSET constants 

Replace `ListLinksSelfPtr::LIST_LINKS_SELF_PTR_OFFSET` with `unsafe fn
raw_get_self_ptr` which returns a pointer to the field rather than
requiring the caller to do pointer arithmetic.

Implement `HasListLinks::raw_get_list_links` in `impl_has_list_links!`,
narrowing the interface of `HasListLinks` and replacing pointer
arithmetic with `container_of!`.

Modify `impl_list_item` to also invoke `impl_has_list_links!` or
`impl_has_list_links_self_ptr!`. This is necessary to allow
`impl_list_item` to see more of the tokens used by
`impl_has_list_links{,_self_ptr}!`.

A similar API change was discussed on the hrtimer series[1].

Link: https://lore.kernel.org/all/20250224-hrtimer-v3-v6-12-rc2-v9-1-5bd3bf0ce6cc@kernel.org/

 [1]
Tested-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Signed-off-by: default avatarTamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250709-list-no-offset-v4-6-a429e75840a9@gmail.com


[ Fixed broken intra-doc links. Used the renamed
  `Opaque::cast_into`. - Miguel ]
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 5d840b4c

rust/kernel/list.rs

+12 −11
Original line number Diff line number Diff line
@@ -57,14 +57,11 @@ 
///     }

/// }

///

/// impl_has_list_links! {

///     impl HasListLinks<0> for BasicItem { self.links }

/// }

/// impl_list_arc_safe! {

///     impl ListArcSafe<0> for BasicItem { untracked; }

/// }

/// impl_list_item! {

///     impl ListItem<0> for BasicItem { using ListLinks; }

///     impl ListItem<0> for BasicItem { using ListLinks { self.links }; }

/// }

///

/// // Create a new empty list.
@@ -320,9 +317,6 @@ unsafe impl<T: ?Sized + Send, const ID: u64> Send for ListLinksSelfPtr<T, ID> {} 
unsafe impl<T: ?Sized + Sync, const ID: u64> Sync for ListLinksSelfPtr<T, ID> {}



impl<T: ?Sized, const ID: u64> ListLinksSelfPtr<T, ID> {

    /// The offset from the [`ListLinks`] to the self pointer field.

    pub const LIST_LINKS_SELF_PTR_OFFSET: usize = core::mem::offset_of!(Self, self_ptr);



    /// 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
@@ -337,6 +331,16 @@ pub fn new() -> impl PinInit<Self> { 
            self_ptr: Opaque::uninit(),

        }

    }



    /// Returns a pointer to the self pointer.

    ///

    /// # Safety

    ///

    /// The provided pointer must point at a valid struct of type `Self`.

    pub unsafe fn raw_get_self_ptr(me: *const Self) -> *const Opaque<*const T> {

        // SAFETY: The caller promises that the pointer is valid.

        unsafe { ptr::addr_of!((*me).self_ptr) }

    }

}



impl<T: ?Sized + ListItem<ID>, const ID: u64> List<T, ID> {
@@ -711,14 +715,11 @@ fn next(&mut self) -> Option<ArcBorrow<'a, T>> { 
///     }

/// }

///

/// kernel::list::impl_has_list_links! {

///     impl HasListLinks<0> for ListItem { self.links }

/// }

/// kernel::list::impl_list_arc_safe! {

///     impl ListArcSafe<0> for ListItem { untracked; }

/// }

/// kernel::list::impl_list_item! {

///     impl ListItem<0> for ListItem { using ListLinks; }

///     impl ListItem<0> for ListItem { using ListLinks { self.links }; }

/// }

///

/// // Use a cursor to remove the first element with the given value.

rust/kernel/list/impl_list_item_mod.rs

+69 −76
Original line number Diff line number Diff line
@@ -4,21 +4,19 @@ 


//! Helpers for implementing list traits safely.



/// Declares that this type has a `ListLinks<ID>` field at a fixed offset.

/// Declares that this type has a [`ListLinks<ID>`] field.

///

/// This trait is only used to help implement `ListItem` safely. If `ListItem` is implemented

/// 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 methods on this trait must have exactly the behavior that the definitions given below have.

///

/// The behavior of `raw_get_list_links` must not be changed.

/// [`ListLinks<ID>`]: crate::list::ListLinks

/// [`ListItem`]: crate::list::ListItem

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
@@ -26,14 +24,7 @@ pub unsafe trait HasListLinks<const ID: u64 = 0> { 
    /// The provided pointer must point at a valid struct of type `Self`.

    ///

    /// [`ListLinks<T, ID>`]: crate::list::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 crate::list::ListLinks<ID> {

        // SAFETY: The caller promises that the pointer is valid. The implementer promises that the

        // `OFFSET` constant is correct.

        unsafe { ptr.cast::<u8>().add(Self::OFFSET).cast() }

    }

    unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut crate::list::ListLinks<ID>;

}



/// Implements the [`HasListLinks`] trait for the given type.
@@ -46,14 +37,15 @@ macro_rules! impl_has_list_links { 
    )*) => {$(

        // 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$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self {

            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>)? {

                // Statically ensure that `$(.field)*` doesn't follow any pointers.

                //

                // Cannot be `const` because `$self` may contain generics and E0401 says constants

                // "can't use {`Self`,generic parameters} from outer item".

                if false { let _: usize = ::core::mem::offset_of!(Self, $($field).*); }



                // 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.
@@ -64,12 +56,16 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$ 
}

pub use impl_has_list_links;



/// Declares that the `ListLinks<ID>` field in this struct is inside a `ListLinksSelfPtr<T, ID>`.

/// Declares that the [`ListLinks<ID>`] field in this struct is inside a

/// [`ListLinksSelfPtr<T, ID>`].

///

/// # Safety

///

/// The `ListLinks<ID>` field of this struct at the offset `HasListLinks<ID>::OFFSET` must be

/// inside a `ListLinksSelfPtr<T, ID>`.

/// The [`ListLinks<ID>`] field of this struct at [`HasListLinks<ID>::raw_get_list_links`] must be

/// inside a [`ListLinksSelfPtr<T, ID>`].

///

/// [`ListLinks<ID>`]: crate::list::ListLinks

/// [`ListLinksSelfPtr<T, ID>`]: crate::list::ListLinksSelfPtr

pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0>

where

    Self: HasListLinks<ID>,
@@ -89,8 +85,6 @@ macro_rules! impl_has_list_links_self_ptr { 
        unsafe impl$(<$($generics)*>)? $crate::list::HasSelfPtr<$item_type $(, $id)?> for $self {}



        unsafe impl$(<$($generics)*>)? $crate::list::HasListLinks$(<$id>)? for $self {

            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.
@@ -120,16 +114,12 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$ 
///     links: kernel::list::ListLinks,

/// }

///

/// kernel::list::impl_has_list_links! {

///     impl HasListLinks<0> for SimpleListItem { self.links }

/// }

///

/// kernel::list::impl_list_arc_safe! {

///     impl ListArcSafe<0> for SimpleListItem { untracked; }

/// }

///

/// kernel::list::impl_list_item! {

///     impl ListItem<0> for SimpleListItem { using ListLinks; }

///     impl ListItem<0> for SimpleListItem { using ListLinks { self.links }; }

/// }

///

/// struct ListLinksHolder {
@@ -143,16 +133,12 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$ 
///     links: ListLinksHolder,

/// }

///

/// kernel::list::impl_has_list_links! {

///     impl{T, U} HasListLinks<0> for ComplexListItem<T, U> { self.links.inner }

/// }

///

/// kernel::list::impl_list_arc_safe! {

///     impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; }

/// }

///

/// kernel::list::impl_list_item! {

///     impl{T, U} ListItem<0> for ComplexListItem<T, U> { using ListLinks; }

///     impl{T, U} ListItem<0> for ComplexListItem<T, U> { using ListLinks { self.links.inner }; }

/// }

/// ```

///
@@ -168,12 +154,8 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$ 
///     impl ListArcSafe<0> for SimpleListItem { untracked; }

/// }

///

/// kernel::list::impl_has_list_links_self_ptr! {

///     impl HasSelfPtr<SimpleListItem> for SimpleListItem { self.links }

/// }

///

/// kernel::list::impl_list_item! {

///     impl ListItem<0> for SimpleListItem { using ListLinksSelfPtr; }

///     impl ListItem<0> for SimpleListItem { using ListLinksSelfPtr { self.links }; }

/// }

///

/// struct ListLinksSelfPtrHolder<T, U> {
@@ -191,21 +173,23 @@ unsafe fn raw_get_list_links(ptr: *mut Self) -> *mut $crate::list::ListLinks$(<$ 
///     impl{T, U} ListArcSafe<0> for ComplexListItem<T, U> { untracked; }

/// }

///

/// kernel::list::impl_has_list_links_self_ptr! {

///     impl{T, U} HasSelfPtr<ComplexListItem<T, U>> for ComplexListItem<T, U> { self.links.inner }

/// }

///

/// kernel::list::impl_list_item! {

///     impl{T, U} ListItem<0> for ComplexListItem<T, U> { using ListLinksSelfPtr; }

///     impl{T, U} ListItem<0> for ComplexListItem<T, U> {

///         using ListLinksSelfPtr { self.links.inner };

///     }

/// }

/// ```

#[macro_export]

macro_rules! impl_list_item {

    (

        $(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty {

            using ListLinks;

            using ListLinks { self$(.$field:ident)* };

        })*

    ) => {$(

        $crate::list::impl_has_list_links! {

            impl$({$($generics)*})? HasListLinks<$num> for $self { self$(.$field)* }

        }



        // SAFETY: See GUARANTEES comment on each method.

        unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self {

            // GUARANTEES:
@@ -221,20 +205,19 @@ unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 
            }



            // 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`.

            // * `me` originates from the most recent call to `prepare_to_insert`, which calls

            //   `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`.

            //   This method uses `container_of` to perform the inverse operation, 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 }

                // points at the field `$field` in a value of type `Self`. Thus, reversing that

                // operation is still in-bounds of the allocation.

                $crate::container_of!(me, Self, $($field).*)

            }



            // GUARANTEES:
@@ -251,25 +234,28 @@ unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$nu 
            }



            // 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`.

            // * `me` originates from the most recent call to `prepare_to_insert`, which calls

            //   `raw_get_list_link`, which is implemented using `addr_of_mut!((*self)$(.$field)*)`.

            //   This method uses `container_of` to perform the inverse operation, 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 }

                // points at the field `$field` in a value of type `Self`. Thus, reversing that

                // operation is still in-bounds of the allocation.

                $crate::container_of!(me, Self, $($field).*)

            }

        }

    )*};



    (

        $(impl$({$($generics:tt)*})? ListItem<$num:tt> for $self:ty {

            using ListLinksSelfPtr;

            using ListLinksSelfPtr { self$(.$field:ident)* };

        })*

    ) => {$(

        $crate::list::impl_has_list_links_self_ptr! {

            impl$({$($generics)*})? HasSelfPtr<$self> for $self { self$(.$field)* }

        }



        // SAFETY: See GUARANTEES comment on each method.

        unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $self {

            // GUARANTEES:
@@ -284,13 +270,15 @@ unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$nu 
                // SAFETY: The caller promises that `me` points at a valid value of type `Self`.

                let links_field = unsafe { <Self as $crate::list::ListItem<$num>>::view_links(me) };



                let spoff = $crate::list::ListLinksSelfPtr::<Self, $num>::LIST_LINKS_SELF_PTR_OFFSET;

                // Goes via the offset as the field is private.

                //

                // SAFETY: The constant is equal to `offset_of!(ListLinksSelfPtr, self_ptr)`, so

                // the pointer stays in bounds of the allocation.

                let self_ptr = unsafe { (links_field as *const u8).add(spoff) }

                    as *const $crate::types::Opaque<*const Self>;

                let container = $crate::container_of!(

                    links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner

                );



                // SAFETY: By the same reasoning above, `links_field` is a valid pointer.

                let self_ptr = unsafe {

                    $crate::list::ListLinksSelfPtr::raw_get_self_ptr(container)

                };



                let cell_inner = $crate::types::Opaque::cast_into(self_ptr);



                // SAFETY: This value is not accessed in any other places than `prepare_to_insert`,
@@ -331,12 +319,17 @@ unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> { 
            //   `ListArc` containing `Self` until the next call to `post_remove`. The value cannot

            //   be destroyed while a `ListArc` reference exists.

            unsafe fn view_value(links_field: *mut $crate::list::ListLinks<$num>) -> *const Self {

                let spoff = $crate::list::ListLinksSelfPtr::<Self, $num>::LIST_LINKS_SELF_PTR_OFFSET;

                // SAFETY: The constant is equal to `offset_of!(ListLinksSelfPtr, self_ptr)`, so

                // the pointer stays in bounds of the allocation.

                let self_ptr = unsafe { (links_field as *const u8).add(spoff) }

                    as *const ::core::cell::UnsafeCell<*const Self>;

                let cell_inner = ::core::cell::UnsafeCell::raw_get(self_ptr);

                let container = $crate::container_of!(

                    links_field, $crate::list::ListLinksSelfPtr<Self, $num>, inner

                );



                // SAFETY: By the same reasoning above, `links_field` is a valid pointer.

                let self_ptr = unsafe {

                    $crate::list::ListLinksSelfPtr::raw_get_self_ptr(container)

                };



                let cell_inner = $crate::types::Opaque::cast_into(self_ptr);



                // SAFETY: This is not a data race, because the only function that writes to this

                // value is `prepare_to_insert`, but by the safety requirements the

                // `prepare_to_insert` method may not be called in parallel with `view_value` or