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

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

> On 6 Aug 2025, at 10:22, Daniel Almeida <daniel.almeida@collabora.com> wrote:
> 
> Hi Andreas,
> 
>> On 11 Jul 2025, at 08:43, 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.
>> 
>> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.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

Ah, I just saw the next patch.

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