On Wed, Nov 29, 2023 at 12:51:07PM +0000, Alice Ryhl wrote:
> This introduces a struct for the EBADF error type, rather than just
> using the Error type directly. This has two advantages:
> * `File::from_fd` returns a `Result<ARef<File>, BadFdError>`, which the
> compiler will represent as a single pointer, with null being an error.
> This is possible because the compiler understands that `BadFdError`
> has only one possible value, and it also understands that the
> `ARef<File>` smart pointer is guaranteed non-null.
> * Additionally, we promise to users of the method that the method can
> only fail with EBADF, which means that they can rely on this promise
> without having to inspect its implementation.
> That said, there are also two disadvantages:
> * Defining additional error types involves boilerplate.
> * The question mark operator will only utilize the `From` trait once,
> which prevents you from using the question mark operator on
> `BadFdError` in methods that return some third error type that the
> kernel `Error` is convertible into. (However, it works fine in methods
> that return `Error`.)
I haven't looked at how Rust-for-Linux handles errors yet, but it's
disappointing to see that it doesn't do something like the PTR_ERR /
ERR_PTR / IS_ERR C thing under the hood.
> @@ -157,6 +158,12 @@ void rust_helper_init_work_with_key(struct work_struct *work, work_func_t func,
> }
> EXPORT_SYMBOL_GPL(rust_helper_init_work_with_key);
>
> +struct file *rust_helper_get_file(struct file *f)
> +{
> + return get_file(f);
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_get_file);
This is ridiculous. A function call instead of doing the
atomic_long_inc() in Rust?
