The most likely thing someone needs a custom hook for is a simple
wrapper function around `write!`. This macro lets them just specify the
format string directly rather than the fully expanded closure.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 rust/kernel/debugfs.rs | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs
index 835df2b5d7311f278d1d15fc8d688809d0ca363f..edc6dd4cc5aedd4d3f1abc1a3793b39fce110d7b 100644
--- a/rust/kernel/debugfs.rs
+++ b/rust/kernel/debugfs.rs
@@ -8,9 +8,9 @@
 
 use crate::error::{from_err_ptr, Result};
 use crate::seq_file::SeqFile;
-use crate::seq_print;
 use crate::str::CStr;
 use crate::types::{ARef, AlwaysRefCounted, Opaque};
+use crate::{debugfs_fmt_file, seq_print};
 use core::fmt;
 use core::fmt::{Display, Formatter};
 use core::marker::{PhantomData, PhantomPinned};
@@ -124,7 +124,7 @@ pub fn display_file<T: Display + Sized>(
         name: &CStr,
         data: &'static T,
     ) -> Result<ARef<Self>> {
-        self.fmt_file(name, data, &|val, f| write!(f, "{val}\n"))
+        debugfs_fmt_file!(self, name, data, "{}\n")
     }
 
     /// Create a file in a DebugFS directory with the provided name, and contents from invoking `f`
@@ -383,7 +383,7 @@ unsafe fn new(inner: &'a Dir) -> Self {
     /// # Ok::<(), Error>(())
     /// ```
     pub fn display_file<T: Display + Sized>(&self, name: &CStr, data: &'a T) -> Result<()> {
-        self.fmt_file(name, data, &|val, f| write!(f, "{val}\n"))
+        debugfs_fmt_file!(self, name, data, "{}\n")
     }
 
     /// Creates a nested directory that may live as long as its parent
@@ -494,3 +494,21 @@ unsafe fn materialize_zst_fmt<F>() -> &'static F {
     // we can materialize it.
     unsafe { zst_dangle.as_ref() }
 }
+
+#[macro_export]
+/// Allows defining a debugfs file with a format string directly
+///
+/// # Example
+///
+/// ```
+/// # use kernel::debugfs::Dir;
+/// # use kernel::{c_str, debugfs_fmt_file};
+/// let dir = Dir::new(c_str!("foo"), None)?;
+/// debugfs_fmt_file!(dir, c_str!("bar"), &3, "bar={}")?;
+/// # Ok::<(), Error>(())
+/// ```
+macro_rules! debugfs_fmt_file {
+    ($dir:expr, $name:expr, $data:expr, $($arg:tt),*) => {
+        $dir.fmt_file($name, $data, &|binding, fmt| write!(fmt, $($arg),*, binding))
+    }
+}

-- 
2.49.0.901.g37484f566f-goog