Re: [PATCH v6 09/18] rust: block: use `NullTerminatedFormatter`

[Daniel Almeida <daniel.almeida@collabora.com>]

> On 22 Aug 2025, at 09:14, Andreas Hindborg <a.hindborg@kernel.org> wrote:
> 
> Use the new `NullTerminatedFormatter` to write the name of a `GenDisk` to
> the name buffer. This new formatter automatically adds a trailing null
> marker after the written characters, so we don't need to append that at the
> call site any longer.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
> rust/kernel/block/mq/gen_disk.rs   | 12 +++++++-----
> rust/kernel/block/mq/raw_writer.rs |  1 +
> rust/kernel/str.rs                 |  1 -
> 3 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
> index 679ee1bb2195..20f1d46c774d 100644
> --- a/rust/kernel/block/mq/gen_disk.rs
> +++ b/rust/kernel/block/mq/gen_disk.rs
> @@ -7,9 +7,11 @@
> 
> use crate::{
>     bindings,
> -    block::mq::{raw_writer::RawWriter, Operations, TagSet},
> +    block::mq::{Operations, TagSet},
>     error::{self, from_err_ptr, Result},
> +    prelude::*,
>     static_lock_class,
> +    str::NullTerminatedFormatter,
>     sync::Arc,
> };
> use core::fmt::{self, Write};
> @@ -143,14 +145,14 @@ pub fn build<T: Operations>(
>         // SAFETY: `gendisk` is a valid pointer as we initialized it above
>         unsafe { (*gendisk).fops = &TABLE };
> 
> -        let mut raw_writer = RawWriter::from_array(
> +        let mut writer = NullTerminatedFormatter::new(
>             // SAFETY: `gendisk` points to a valid and initialized instance. We
>             // have exclusive access, since the disk is not added to the VFS
>             // yet.
>             unsafe { &mut (*gendisk).disk_name },
> -        )?;
> -        raw_writer.write_fmt(name)?;
> -        raw_writer.write_char('\0')?;
> +        )
> +        .ok_or(EINVAL)?;
> +        writer.write_fmt(name)?;
> 
>         // SAFETY: `gendisk` points to a valid and initialized instance of
>         // `struct gendisk`. `set_capacity` takes a lock to synchronize this
> diff --git a/rust/kernel/block/mq/raw_writer.rs b/rust/kernel/block/mq/raw_writer.rs
> index 7e2159e4f6a6..0aef55703e71 100644
> --- a/rust/kernel/block/mq/raw_writer.rs
> +++ b/rust/kernel/block/mq/raw_writer.rs
> @@ -24,6 +24,7 @@ fn new(buffer: &'a mut [u8]) -> Result<RawWriter<'a>> {
>         Ok(Self { buffer, pos: 0 })
>     }
> 
> +    #[expect(dead_code)]
>     pub(crate) fn from_array<const N: usize>(
>         a: &'a mut [crate::ffi::c_char; N],
>     ) -> Result<RawWriter<'a>> {
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index b185262b4851..a3e34f566034 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -886,7 +886,6 @@ pub(crate) struct NullTerminatedFormatter<'a> {
> 
> impl<'a> NullTerminatedFormatter<'a> {
>     /// Create a new [`Self`] instance.
> -    #[expect(dead_code)]
>     pub(crate) fn new(buffer: &'a mut [u8]) -> Option<NullTerminatedFormatter<'a>> {
>         *(buffer.first_mut()?) = 0;
> 
> 
> -- 
> 2.47.2
> 
> 
> 

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>