linux-kernel - [PATCH v2 05/14] rust: block: use `NullBorrowFormatter`

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Message-Id: <20250708-rnull-up-v6-16-v2-5-ab93c0ff429b@kernel.org>
Date: Tue, 08 Jul 2025 21:45:00 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: 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>
Cc: linux-block@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v2 05/14] rust: block: use `NullBorrowFormatter`

Use the new `NullBorrowFormatter` 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   | 8 ++++----
 rust/kernel/block/mq/raw_writer.rs | 1 +
 rust/kernel/str.rs                 | 7 -------
 3 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
index 679ee1bb21950..e0e42f7028276 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::NullBorrowFormatter,
     sync::Arc,
 };
 use core::fmt::{self, Write};
@@ -143,14 +144,13 @@ 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 = NullBorrowFormatter::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')?;
+        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 7e2159e4f6a6f..0aef55703e71d 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 05d79cf40c201..4140b4af64e50 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -881,7 +881,6 @@ pub(crate) fn new(buffer: &'a mut [u8]) -> Result<NullBorrowFormatter<'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<NullBorrowFormatter<'a>> {
@@ -891,12 +890,6 @@ pub(crate) fn from_array<const N: usize>(
             unsafe { core::slice::from_raw_parts_mut(a.as_mut_ptr().cast::<u8>(), N) },
         )
     }
-
-    /// Return the position of the write pointer in the underlying buffer.
-    #[expect(dead_code)]
-    pub(crate) fn pos(&self) -> usize {
-        self.pos
-    }
 }
 
 impl Write for NullBorrowFormatter<'_> {

-- 
2.47.2