Re: [PATCH v6 1/4] rust: uaccess: add userspace pointers

[Alice Ryhl]

On Fri, Apr 19, 2024 at 7:11 PM Boqun Feng <boqun.feng@xxxxxxxxx> wrote:
>
> On Thu, Apr 18, 2024 at 08:59:17AM +0000, Alice Ryhl wrote:
> [...]
> > +    /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
> > +    ///
> > +    /// Fails with `EFAULT` if the read happens on a bad address.
> > +    pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
> > +        let len = self.length;
> > +        buf.reserve(len, flags)?;
>
> (Reportedy by Miguel)
>
> When compile with `make rusttest`, kernel crate is compiled as userspace
> program, so we need to explicitly pick where the `reserve` comes from
> (Vec or VecExt), the current version will hit the following error:
>
>         error[E0061]: this method takes 1 argument but 2 arguments were supplied
>            --> rust/kernel/uaccess.rs:296:13
>             |
>         296 |         buf.reserve(len, flags)?;
>             |             ^^^^^^^    -------
>             |                        | |
>             |                        | unexpected argument of type `Flags`
>             |                        help: remove the extra argument
>             |
>         note: method defined here
>            --> /home/boqun/linux-rust/rust/test/sysroot/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:910:12
>             |
>         910 |     pub fn reserve(&mut self, additional: usize) {
>             |            ^^^^^^^
>
>         error[E0277]: the `?` operator can only be applied to values that implement `Try`
>            --> rust/kernel/uaccess.rs:296:9
>             |
>         296 |         buf.reserve(len, flags)?;
>             |         ^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `()`
>             |
>             = help: the trait `Try` is not implemented for `()`
>
>         error: aborting due to 2 previous errors
>
>         Some errors have detailed explanations: E0061, E0277.
>         For more information about an error, try `rustc --explain E0061`.
>
> and we need to the following fix
>
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index 39481e374c40..80f7e7ca2f5e 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -293,7 +293,7 @@ pub fn read<T: FromBytes>(&mut self) -> Result<T> {
>      /// Fails with `EFAULT` if the read happens on a bad address.
>      pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
>          let len = self.length;
> -        buf.reserve(len, flags)?;
> +        VecExt::<u8>::reserve(buf, len, flags)?;
>
>          // The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
>          // long.

I'm sorry, what? This seems like a problem with `make rusttest`.

Alice