rust: debugfs: drop 'static bound from ScopedDir file creation methods

Drop the T: 'static bound from ScopedDir's file creation methods
(read_binary_file(), read_only_file(), etc.) to support registering
debugfs files backed by types that contain non-'static references, such
as dma::Coherent<'a, T>.

The previous 'static bound existed because ScopedDir::create_file() took
&'static FileOps<T>, and &'static requires T: 'static for well-
formedness. However, this was overly conservative: the file_operations
pointer passed to the C debugfs API just needs to be 'static, not the
entire FileOps<T>.

Store &'static bindings::file_operations in FileOps<T> instead of the
file_operations by value. In each trait impl, take a reference to the
file_operations struct within the const block; since
bindings::file_operations does not mention T, the reference is promoted
to 'static regardless of T's lifetime parameters.

Replace the Deref impl with an explicit fops() method that returns the
stored &'static reference.

Link: https://lore.kernel.org/driver-core/20260830193824.471089-2-dakr@kernel.org
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260830193824.471089-2-dakr@kernel.org
[ Remove unrelated change from Self to T. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

2 files changed, 15 insertions, 18 deletions

diff --git a/rust/kernel/debugfs/entry.rs b/rust/kernel/debugfs/entry.rs
index 46aad64896ec..88a870d8c295 100644
--- a/rust/kernel/debugfs/entry.rs
+++ b/rust/kernel/debugfs/entry.rs
@@ -74,7 +74,7 @@ impl Entry<'static> {
                 parent.as_ptr(),
                 core::ptr::from_ref(data) as *mut c_void,
                 core::ptr::null(),
-                &**file_ops,
+                file_ops.fops(),
             )
         };
 
@@ -127,7 +127,7 @@ impl<'a> Entry<'a> {
                 parent.as_ptr(),
                 core::ptr::from_ref(data) as *mut c_void,
                 core::ptr::null(),
-                &**file_ops,
+                file_ops.fops(),
             )
         };
 
diff --git a/rust/kernel/debugfs/file_ops.rs b/rust/kernel/debugfs/file_ops.rs
index f15908f71c4a..47acc4851d47 100644
--- a/rust/kernel/debugfs/file_ops.rs
+++ b/rust/kernel/debugfs/file_ops.rs
@@ -20,9 +20,6 @@ use crate::{
 
 use core::marker::PhantomData;
 
-#[cfg(CONFIG_DEBUG_FS)]
-use core::ops::Deref;
-
 /// # Invariant
 ///
 /// `FileOps<T>` will always contain an `operations` which is safe to use for a file backed
@@ -30,7 +27,7 @@ use core::ops::Deref;
 /// into a reference.
 pub(super) struct FileOps<T> {
     #[cfg(CONFIG_DEBUG_FS)]
-    operations: bindings::file_operations,
+    operations: &'static bindings::file_operations,
     #[cfg(CONFIG_DEBUG_FS)]
     mode: u16,
     _phantom: PhantomData<T>,
@@ -41,7 +38,7 @@ impl<T> FileOps<T> {
     ///
     /// The caller asserts that the provided `operations` is safe to use for a file whose
     /// inode has a pointer to `T` in its private data that is safe to convert into a reference.
-    const unsafe fn new(operations: bindings::file_operations, mode: u16) -> Self {
+    const unsafe fn new(operations: &'static bindings::file_operations, mode: u16) -> Self {
         Self {
             #[cfg(CONFIG_DEBUG_FS)]
             operations,
@@ -65,11 +62,11 @@ impl<T: Adapter> FileOps<T> {
 }
 
 #[cfg(CONFIG_DEBUG_FS)]
-impl<T> Deref for FileOps<T> {
-    type Target = bindings::file_operations;
-
-    fn deref(&self) -> &Self::Target {
-        &self.operations
+impl<T> FileOps<T> {
+    /// Returns a `'static` reference to the inner `file_operations`.
+    #[inline]
+    pub(crate) fn fops(&self) -> &'static bindings::file_operations {
+        self.operations
     }
 }
 
@@ -130,7 +127,7 @@ pub(crate) trait ReadFile<T> {
 
 impl<T: Writer + Sync> ReadFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             read: Some(bindings::seq_read),
             llseek: Some(bindings::seq_lseek),
             release: Some(bindings::single_release),
@@ -181,7 +178,7 @@ pub(crate) trait ReadWriteFile<T> {
 
 impl<T: Writer + Reader + Sync> ReadWriteFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             open: Some(writer_open::<T>),
             read: Some(bindings::seq_read),
             write: Some(write::<T>),
@@ -238,7 +235,7 @@ pub(crate) trait WriteFile<T> {
 
 impl<T: Reader + Sync> WriteFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             open: Some(write_only_open),
             write: Some(write_only_write::<T>),
             llseek: Some(bindings::noop_llseek),
@@ -290,7 +287,7 @@ pub(crate) trait BinaryReadFile<T> {
 
 impl<T: BinaryWriter + Sync> BinaryReadFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             read: Some(blob_read::<T>),
             llseek: Some(bindings::default_llseek),
             open: Some(bindings::simple_open),
@@ -344,7 +341,7 @@ pub(crate) trait BinaryWriteFile<T> {
 
 impl<T: BinaryReader + Sync> BinaryWriteFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             write: Some(blob_write::<T>),
             llseek: Some(bindings::default_llseek),
             open: Some(bindings::simple_open),
@@ -368,7 +365,7 @@ pub(crate) trait BinaryReadWriteFile<T> {
 
 impl<T: BinaryWriter + BinaryReader + Sync> BinaryReadWriteFile<T> for T {
     const FILE_OPS: FileOps<T> = {
-        let operations = bindings::file_operations {
+        let operations = &bindings::file_operations {
             read: Some(blob_read::<T>),
             write: Some(blob_write::<T>),
             llseek: Some(bindings::default_llseek),