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

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Message-ID: <874iuk8pqr.fsf@kernel.org>
Date: Wed, 06 Aug 2025 16:54:36 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Daniel Almeida <daniel.almeida@...labora.com>
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`

"Daniel Almeida" <daniel.almeida@...labora.com> writes:

> 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>> {
>>

Yes. Alice suggested combining patch 8/16 that removes
`block::mq::raw_writer` with this one.


Best regards,
Andreas Hindborg