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Previously, the `ForeignOwnable` trait had a method called `borrow_mut` that was intended to provide mutable access to the inner value. However, the method accidentally made it possible to change the address of the object being modified, which usually isn't what we want. (And when we want that, it can be done by calling `from_foreign` and `into_foreign`, like how the old `borrow_mut` was implemented.) In this patch, we introduce an alternate definition of `borrow_mut` that solves the previous problem. Conceptually, given a pointer type `P` that implements `ForeignOwnable`, the `borrow_mut` method gives you the same kind of access as an `&mut P` would, except that it does not let you change the pointer `P` itself. This is analogous to how the existing `borrow` method provides the same kind of access to the inner value as an `&P`. Note that for types like `Arc`, having an `&mut Arc<T>` only gives you immutable access to the inner `T`. This is because mutable references assume exclusive access, but there might be other handles to the same reference counted value, so the access isn't exclusive. The `Arc` type implements this by making `borrow_mut` return the same type as `borrow`. Signed-off-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org> Signed-off-by: Tamir Duberstein <tamird@gmail.com> Acked-by: Danilo Krummrich <dakr@kernel.org> Link: https://lore.kernel.org/r/20241120-borrow-mut-v6-6-80dbadd00951@gmail.com [ Updated to `crate::ffi::`. Reworded title slightly. - Miguel ] Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.