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 <[email protected]>

Author: Andreas Hindborg

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 @@ impl GenDiskBuilder {
         // 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

rust/kernel/block/mq/raw_writer.rs

@@ -24,6 +24,7 @@ impl<'a> 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>> {

rust/kernel/str.rs

@@ -881,7 +881,6 @@ impl<'a> 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 @@ impl<'a> NullBorrowFormatter<'a> {
             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<'_> {