Support linked lists that can have many different structs at once. This
is generally done using trait objects. The main challenge is figuring
what the struct is given only a pointer to the ListLinks.
We do this by storing a pointer to the struct next to the ListLinks
field. The container_of operation will then just read that pointer. When
the type is a trait object, that pointer will be a fat pointer whose
metadata is a vtable that tells you what kind of struct it is.
Heterogeneous lists are heavily used by Rust Binder. There are a lot of
so-called todo lists containing various events that need to be delivered
to userspace next time userspace calls into the driver. And there are
quite a few different todo item types: incoming transaction, changes to
refcounts, death notifications, and more.
Signed-off-by: Alice Ryhl <[email protected]>
---
rust/kernel/list.rs | 47 ++++++++++++++-
rust/kernel/list/impl_list_item_mod.rs | 105 +++++++++++++++++++++++++++++++++
2 files changed, 151 insertions(+), 1 deletion(-)
diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
index 641b434e3841..3e687401c6d3 100644
--- a/rust/kernel/list.rs
+++ b/rust/kernel/list.rs
@@ -7,12 +7,16 @@
use crate::init::PinInit;
use crate::sync::ArcBorrow;
use crate::types::Opaque;
+use core::cell::UnsafeCell;
use core::iter::{DoubleEndedIterator, FusedIterator};
use core::marker::PhantomData;
+use core::mem::MaybeUninit;
use core::ptr;
mod impl_list_item_mod;
-pub use self::impl_list_item_mod::{impl_has_list_links, impl_list_item, HasListLinks};
+pub use self::impl_list_item_mod::{
+ impl_has_list_links, impl_has_list_links_self_ptr, impl_list_item, HasListLinks, HasSelfPtr,
+};
mod arc;
pub use self::arc::{
@@ -180,6 +184,47 @@ unsafe fn from_fields(me: *mut ListLinksFields) -> *mut Self {
}
}
+/// Similar to [`ListLinks`], but also contains a pointer to the full value.
+///
+/// This type can be used instead of [`ListLinks`] to support lists with trait objects.
+#[repr(C)]
+pub struct ListLinksSelfPtr<T: ?Sized, const ID: u64 = 0> {
+ /// The `ListLinks` field inside this value.
+ ///
+ /// This is public so that it can be used with `impl_has_list_links!`.
+ pub inner: ListLinks<ID>,
+ self_ptr: UnsafeCell<MaybeUninit<*const T>>,
+}
+
+// SAFETY: The fields of a ListLinksSelfPtr can be moved across thread boundaries.
+unsafe impl<T: ?Sized + Send, const ID: u64> Send for ListLinksSelfPtr<T, ID> {}
+// SAFETY: The type is opaque so immutable references to a ListLinksSelfPtr are useless. Therefore,
+// it's okay to have immutable access to a ListLinks from several threads at once.
+//
+// Note that `inner` being a public field does not prevent this type from being opaque, since
+// `inner` is a opaque type.
+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
+ // not be constructed in an `Arc` that already has a `ListArc`.
+ Self {
+ inner: ListLinks {
+ inner: Opaque::new(ListLinksFields {
+ prev: ptr::null_mut(),
+ next: ptr::null_mut(),
+ }),
+ },
+ self_ptr: UnsafeCell::new(MaybeUninit::zeroed()),
+ }
+ }
+}
+
impl<T: ?Sized + ListItem<ID>, const ID: u64> List<T, ID> {
/// Creates a new empty list.
pub const fn new() -> Self {
diff --git a/rust/kernel/list/impl_list_item_mod.rs b/rust/kernel/list/impl_list_item_mod.rs
index 3ff483be89d1..96e90c0ec587 100644
--- a/rust/kernel/list/impl_list_item_mod.rs
+++ b/rust/kernel/list/impl_list_item_mod.rs
@@ -62,6 +62,49 @@ 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>`.
+///
+/// # Safety
+///
+/// The `ListLinks<ID>` field of this struct at the offset `HasListLinks<ID>::OFFSET` must be
+/// inside a `ListLinksSelfPtr<T, ID>`.
+pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0>
+where
+ Self: HasListLinks<ID>,
+{
+}
+
+/// Implements the [`HasListLinks`] and [`HasSelfPtr`] traits for the given type.
+#[macro_export]
+macro_rules! impl_has_list_links_self_ptr {
+ ($(impl$({$($implarg:tt)*})?
+ HasSelfPtr<$item_type:ty $(, $id:tt)?>
+ for $self:ident $(<$($selfarg:ty),*>)?
+ { self.$field:ident }
+ )*) => {$(
+ // SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the
+ // right type.
+ unsafe impl$(<$($implarg)*>)? $crate::list::HasSelfPtr<$item_type $(, $id)?> for
+ $self $(<$($selfarg),*>)?
+ {}
+
+ unsafe impl$(<$($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.
+ let ptr: *mut $crate::list::ListLinksSelfPtr<$item_type $(, $id)?> =
+ unsafe { ::core::ptr::addr_of_mut!((*ptr).$field) };
+ ptr.cast()
+ }
+ }
+ )*};
+}
+pub use impl_has_list_links_self_ptr;
+
/// Implements the [`ListItem`] trait for the given type.
///
/// Assumes that the type implements [`HasListLinks`].
@@ -95,5 +138,67 @@ unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
}
}
};
+
+ (
+ impl$({$($generics:tt)*})? ListItem<$num:tt> for $t:ty {
+ using ListLinksSelfPtr;
+ } $($rest:tt)*
+ ) => {
+ unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $t {
+ unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
+ // 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;
+ // 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);
+
+ // SAFETY: This value is not accessed in any other places than `prepare_to_insert`,
+ // `post_remove`, or `view_value`. By the safety requirements of those methods,
+ // none of these three methods may be called in parallel with this call to
+ // `prepare_to_insert`, so this write will not race with any other access to the
+ // value.
+ unsafe { ::core::ptr::write(cell_inner, me) };
+
+ links_field
+ }
+
+ unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
+ // SAFETY: The caller promises that `me` points at a valid value of type `Self`.
+ unsafe { <Self as HasListLinks<$num>>::raw_get_list_links(me.cast_mut()) }
+ }
+
+ // This function is also used as the implementation of `post_remove`, so the caller
+ // may choose to satisfy the safety requirements of `post_remove` instead of the safety
+ // requirements for `view_value`.
+ 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);
+ // This returns the same pointer as the one passes to the previous call to
+ // `prepare_to_insert` since that previous call wrote that pointer to this
+ // location, and the value has not been modified since.
+ //
+ // 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
+ // `post_remove`.
+ unsafe { ::core::ptr::read(cell_inner) }
+ }
+
+ unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
+ // SAFETY: This specific implementation of `view_value` allows the caller to
+ // promise the safety requirements of `post_remove` instead of the safety
+ // requirements for `view_value`.
+ unsafe { <Self as $crate::list::ListItem<$num>>::view_value(me) }
+ }
+ }
+ };
}
pub use impl_list_item;
--
2.45.0.rc1.225.g2a3ae87e7f-goog
On 06.05.24 11:53, Alice Ryhl wrote:
> Support linked lists that can have many different structs at once. This
have -> hold
> is generally done using trait objects. The main challenge is figuring
> what the struct is given only a pointer to the ListLinks.
>
> We do this by storing a pointer to the struct next to the ListLinks
> field. The container_of operation will then just read that pointer. When
> the type is a trait object, that pointer will be a fat pointer whose
> metadata is a vtable that tells you what kind of struct it is.
>
> Heterogeneous lists are heavily used by Rust Binder. There are a lot of
> so-called todo lists containing various events that need to be delivered
> to userspace next time userspace calls into the driver. And there are
> quite a few different todo item types: incoming transaction, changes to
> refcounts, death notifications, and more.
>
> Signed-off-by: Alice Ryhl <[email protected]>
> ---
> rust/kernel/list.rs | 47 ++++++++++++++-
> rust/kernel/list/impl_list_item_mod.rs | 105 +++++++++++++++++++++++++++++++++
> 2 files changed, 151 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
> index 641b434e3841..3e687401c6d3 100644
> --- a/rust/kernel/list.rs
> +++ b/rust/kernel/list.rs
> @@ -7,12 +7,16 @@
> use crate::init::PinInit;
> use crate::sync::ArcBorrow;
> use crate::types::Opaque;
> +use core::cell::UnsafeCell;
> use core::iter::{DoubleEndedIterator, FusedIterator};
> use core::marker::PhantomData;
> +use core::mem::MaybeUninit;
> use core::ptr;
>
> mod impl_list_item_mod;
> -pub use self::impl_list_item_mod::{impl_has_list_links, impl_list_item, HasListLinks};
> +pub use self::impl_list_item_mod::{
> + impl_has_list_links, impl_has_list_links_self_ptr, impl_list_item, HasListLinks, HasSelfPtr,
> +};
>
> mod arc;
> pub use self::arc::{
> @@ -180,6 +184,47 @@ unsafe fn from_fields(me: *mut ListLinksFields) -> *mut Self {
> }
> }
>
> +/// Similar to [`ListLinks`], but also contains a pointer to the full value.
> +///
> +/// This type can be used instead of [`ListLinks`] to support lists with trait objects.
> +#[repr(C)]
> +pub struct ListLinksSelfPtr<T: ?Sized, const ID: u64 = 0> {
> + /// The `ListLinks` field inside this value.
> + ///
> + /// This is public so that it can be used with `impl_has_list_links!`.
> + pub inner: ListLinks<ID>,
> + self_ptr: UnsafeCell<MaybeUninit<*const T>>,
Why don't you use `Opaque` instead?
> +}
> +
> +// SAFETY: The fields of a ListLinksSelfPtr can be moved across thread boundaries.
> +unsafe impl<T: ?Sized + Send, const ID: u64> Send for ListLinksSelfPtr<T, ID> {}
> +// SAFETY: The type is opaque so immutable references to a ListLinksSelfPtr are useless. Therefore,
> +// it's okay to have immutable access to a ListLinks from several threads at once.
> +//
> +// Note that `inner` being a public field does not prevent this type from being opaque, since
> +// `inner` is a opaque type.
> +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
> + // not be constructed in an `Arc` that already has a `ListArc`.
> + Self {
> + inner: ListLinks {
> + inner: Opaque::new(ListLinksFields {
> + prev: ptr::null_mut(),
> + next: ptr::null_mut(),
> + }),
> + },
> + self_ptr: UnsafeCell::new(MaybeUninit::zeroed()),
> + }
> + }
> +}
> +
> impl<T: ?Sized + ListItem<ID>, const ID: u64> List<T, ID> {
> /// Creates a new empty list.
> pub const fn new() -> Self {
> diff --git a/rust/kernel/list/impl_list_item_mod.rs b/rust/kernel/list/impl_list_item_mod.rs
> index 3ff483be89d1..96e90c0ec587 100644
> --- a/rust/kernel/list/impl_list_item_mod.rs
> +++ b/rust/kernel/list/impl_list_item_mod.rs
> @@ -62,6 +62,49 @@ 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>`.
> +///
> +/// # Safety
> +///
> +/// The `ListLinks<ID>` field of this struct at the offset `HasListLinks<ID>::OFFSET` must be
> +/// inside a `ListLinksSelfPtr<T, ID>`.
> +pub unsafe trait HasSelfPtr<T: ?Sized, const ID: u64 = 0>
> +where
> + Self: HasListLinks<ID>,
> +{
> +}
> +
> +/// Implements the [`HasListLinks`] and [`HasSelfPtr`] traits for the given type.
> +#[macro_export]
> +macro_rules! impl_has_list_links_self_ptr {
> + ($(impl$({$($implarg:tt)*})?
> + HasSelfPtr<$item_type:ty $(, $id:tt)?>
> + for $self:ident $(<$($selfarg:ty),*>)?
> + { self.$field:ident }
> + )*) => {$(
> + // SAFETY: The implementation of `raw_get_list_links` only compiles if the field has the
> + // right type.
> + unsafe impl$(<$($implarg)*>)? $crate::list::HasSelfPtr<$item_type $(, $id)?> for
> + $self $(<$($selfarg),*>)?
> + {}
> +
> + unsafe impl$(<$($implarg)*>)? $crate::list::HasListLinks$(<$id>)? for
Missing SAFETY comment.
> + $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.
> + let ptr: *mut $crate::list::ListLinksSelfPtr<$item_type $(, $id)?> =
> + unsafe { ::core::ptr::addr_of_mut!((*ptr).$field) };
> + ptr.cast()
> + }
> + }
> + )*};
> +}
> +pub use impl_has_list_links_self_ptr;
> +
> /// Implements the [`ListItem`] trait for the given type.
> ///
> /// Assumes that the type implements [`HasListLinks`].
> @@ -95,5 +138,67 @@ unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
> }
> }
> };
> +
> + (
> + impl$({$($generics:tt)*})? ListItem<$num:tt> for $t:ty {
> + using ListLinksSelfPtr;
> + } $($rest:tt)*
> + ) => {
> + unsafe impl$(<$($generics)*>)? $crate::list::ListItem<$num> for $t {
Missing SAFETY comment.
---
Cheers,
Benno
> + unsafe fn prepare_to_insert(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
> + // 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;
> + // 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);
> +
> + // SAFETY: This value is not accessed in any other places than `prepare_to_insert`,
> + // `post_remove`, or `view_value`. By the safety requirements of those methods,
> + // none of these three methods may be called in parallel with this call to
> + // `prepare_to_insert`, so this write will not race with any other access to the
> + // value.
> + unsafe { ::core::ptr::write(cell_inner, me) };
> +
> + links_field
> + }
> +
> + unsafe fn view_links(me: *const Self) -> *mut $crate::list::ListLinks<$num> {
> + // SAFETY: The caller promises that `me` points at a valid value of type `Self`.
> + unsafe { <Self as HasListLinks<$num>>::raw_get_list_links(me.cast_mut()) }
> + }
> +
> + // This function is also used as the implementation of `post_remove`, so the caller
> + // may choose to satisfy the safety requirements of `post_remove` instead of the safety
> + // requirements for `view_value`.
> + 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);
> + // This returns the same pointer as the one passes to the previous call to
> + // `prepare_to_insert` since that previous call wrote that pointer to this
> + // location, and the value has not been modified since.
> + //
> + // 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
> + // `post_remove`.
> + unsafe { ::core::ptr::read(cell_inner) }
> + }
> +
> + unsafe fn post_remove(me: *mut $crate::list::ListLinks<$num>) -> *const Self {
> + // SAFETY: This specific implementation of `view_value` allows the caller to
> + // promise the safety requirements of `post_remove` instead of the safety
> + // requirements for `view_value`.
> + unsafe { <Self as $crate::list::ListItem<$num>>::view_value(me) }
> + }
> + }
> + };
> }
> pub use impl_list_item;
>
> --
> 2.45.0.rc1.225.g2a3ae87e7f-goog
>