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rust: add container_of! macro

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This macro is used to obtain a pointer to an entire struct
when given a pointer to a field in that struct.

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>
Link: https://lore.kernel.org/r/20240219-b4-rbtree-v2-1-0b113aab330d@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Wedson Almeida Filho 2024-02-19 11:48:08 +00:00 committed by Miguel Ojeda
parent 4951ddd51b
commit e944171070
1 changed files with 32 additions and 0 deletions
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32
rust/kernel/lib.rs
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@ -101,3 +101,35 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
// SAFETY: FFI call.
unsafe { bindings::BUG() };
}
/// Produces a pointer to an object from a pointer to one of its fields.
///
/// # Safety
///
/// The pointer passed to this macro, and the pointer returned by this macro, must both be in
/// bounds of the same allocation.
///
/// # Examples
///
/// ```
/// # use kernel::container_of;
/// struct Test {
/// a: u64,
/// b: u32,
/// }
///
/// let test = Test { a: 10, b: 20 };
/// let b_ptr = &test.b;
/// // SAFETY: The pointer points at the `b` field of a `Test`, so the resulting pointer will be
/// // in-bounds of the same allocation as `b_ptr`.
/// let test_alias = unsafe { container_of!(b_ptr, Test, b) };
/// assert!(core::ptr::eq(&test, test_alias));
/// ```
#[macro_export]
macro_rules! container_of {
($ptr:expr, $type:ty, $($f:tt)*) => {{
let ptr = $ptr as *const _ as *const u8;
let offset: usize = ::core::mem::offset_of!($type, $($f)*);
ptr.sub(offset) as *const $type
}}
}