Commit 6c2d0ad5 authored by Alice Ryhl's avatar Alice Ryhl Committed by Miguel Ojeda
Browse files

rust: implement ForeignOwnable for Pin<Box<T>> 



We already implement ForeignOwnable for Box<T>, but it may be useful to
store pinned data in a ForeignOwnable container. This patch makes that
possible.

This will be used together with upcoming miscdev abstractions, which
Binder will use when binderfs is disabled.

Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarBenno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20240730-foreign-ownable-pin-box-v1-1-b1d70cdae541@google.com


Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 08f983a5

rust/kernel/types.rs

+27 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
    marker::{PhantomData, PhantomPinned},

    mem::MaybeUninit,

    ops::{Deref, DerefMut},

    pin::Pin,

    ptr::NonNull,

};
@@ -89,6 +90,32 @@ unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self { 
    }

}



impl<T: 'static> ForeignOwnable for Pin<Box<T>> {

    type Borrowed<'a> = Pin<&'a T>;



    fn into_foreign(self) -> *const core::ffi::c_void {

        // SAFETY: We are still treating the box as pinned.

        Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }) as _

    }



    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Pin<&'a T> {

        // SAFETY: The safety requirements for this function ensure that the object is still alive,

        // so it is safe to dereference the raw pointer.

        // The safety requirements of `from_foreign` also ensure that the object remains alive for

        // the lifetime of the returned value.

        let r = unsafe { &*ptr.cast() };



        // SAFETY: This pointer originates from a `Pin<Box<T>>`.

        unsafe { Pin::new_unchecked(r) }

    }



    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {

        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous

        // call to `Self::into_foreign`.

        unsafe { Pin::new_unchecked(Box::from_raw(ptr as _)) }

    }

}



impl ForeignOwnable for () {

    type Borrowed<'a> = ();