linux-kernel - Re: [PATCH v3 07/16] rust: block: use `NullTerminatedFormatter`

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Message-Id: <2B209DA7-1989-40EF-9535-2A9CC98E0980@collabora.com>
Date: Wed, 6 Aug 2025 10:22:45 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>,
 Jens Axboe <axboe@...nel.dk>,
 linux-block@...r.kernel.org,
 rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/16] rust: block: use `NullTerminatedFormatter`

Hi Andreas,

> On 11 Jul 2025, at 08:43, Andreas Hindborg <a.hindborg@...nel.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.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
> rust/kernel/block/mq/gen_disk.rs   | 11 ++++++-----
> rust/kernel/block/mq/raw_writer.rs |  1 +
> rust/kernel/str.rs                 |  1 -
> 3 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
> index 679ee1bb2195..39be2a31337f 100644
> --- a/rust/kernel/block/mq/gen_disk.rs
> +++ b/rust/kernel/block/mq/gen_disk.rs
> @@ -7,9 +7,10 @@
> 
> use crate::{
>     bindings,
> -    block::mq::{raw_writer::RawWriter, Operations, TagSet},
> +    block::mq::{Operations, TagSet},
>     error::{self, from_err_ptr, Result},
>     static_lock_class,
> +    str::NullTerminatedFormatter,
>     sync::Arc,
> };
> use core::fmt::{self, Write};
> @@ -143,14 +144,14 @@ 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::from_array(
>             // 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(error::code::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)]

Not sure I understand, is this superseded by..

>     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 c58925438c6e..7396c49174cd 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -858,7 +858,6 @@ pub(crate) fn new(buffer: &'a mut [u8]) -> Option<NullTerminatedFormatter<'a>> {
>         Some(Self { buffer })
>     }
> 
> -    #[expect(dead_code)]

… this?

>     pub(crate) fn from_array<const N: usize>(
>         buffer: &'a mut [crate::ffi::c_char; N],
>     ) -> Option<NullTerminatedFormatter<'a>> {
> 
> -- 
> 2.47.2
> 
> 
> 

— Daniel