Re: [PATCH] uaccess: rust: add strncpy_from_user

[Danilo Krummrich <dakr@kernel.org>]

On Thu, Apr 24, 2025 at 03:17:48PM +0000, Alice Ryhl wrote:
> 
> +/// Reads a nul-terminated string into `buf` and returns the length.
> +///
> +/// Fails with [`EFAULT`] if the read happens on a bad address. If the end of `buf` is reached,
> +/// then the buffer will not be nul-terminated.
> +#[inline]
> +pub fn strncpy_from_user(ptr: UserPtr, buf: &mut [u8]) -> Result<usize> {

Should probably be named strcpy_from_user() instead.

> +    // CAST: Slice lengths are guaranteed to be `<= isize::MAX`.
> +    let len = buf.len() as isize;
> +
> +    // SAFETY: `buf` is valid for writing `buf.len()` bytes.
> +    let res = unsafe {
> +        bindings::strncpy_from_user(
> +            buf.as_mut_ptr(),
> +            ptr as *const u8,

kernel::ffi::c_char should always match u8, but should we use the FFI type
regardless?