On Thu Sep 3, 2026 at 3:12 PM CEST, Gary Guo wrote: > This can be better done by storing `&'static bindings::file_operations` in > `FileOps<T>` instead of just by value. That is actually better than the > current > impl, IMO, because `mode` for example doesn't have to be in static storage. > (You > can also then make `FileOps<T>` `Copy`).
That's a great suggestion, thanks. It simplifies the patch to: Author: Danilo Krummrich <[email protected]> Date: Sat Aug 29 14:42:54 2026 +0200 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. Signed-off-by: Danilo Krummrich <[email protected]> diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs index d7b8014a6474..2beb55d444ca 100644 --- a/rust/kernel/debugfs.rs +++ b/rust/kernel/debugfs.rs @@ -538,7 +538,7 @@ pub fn dir<'dir2>(&'dir2 self, name: &CStr) -> ScopedDir<'data, 'dir2> { } } - fn create_file<T: Sync>(&self, name: &CStr, data: &'data T, vtable: &'static FileOps<T>) { + fn create_file<T: Sync>(&self, name: &CStr, data: &'data T, vtable: &FileOps<T>) { #[cfg(CONFIG_DEBUG_FS)] core::mem::forget(Entry::file(name, &self.entry, data, vtable)); } @@ -550,7 +550,7 @@ fn create_file<T: Sync>(&self, name: &CStr, data: &'data T, vtable: &'static Fil /// This function does not produce an owning handle to the file. The created /// file is removed when the [`Scope`] that this directory belongs /// to is dropped. - pub fn read_only_file<T: Writer + Send + Sync + 'static>(&self, name: &CStr, data: &'data T) { + pub fn read_only_file<T: Writer + Send + Sync>(&self, name: &CStr, data: &'data T) { self.create_file(name, data, &T::FILE_OPS) } @@ -560,11 +560,7 @@ pub fn read_only_file<T: Writer + Send + Sync + 'static>(&self, name: &CStr, dat /// /// This function does not produce an owning handle to the file. The created file is removed /// when the [`Scope`] that this directory belongs to is dropped. - pub fn read_binary_file<T: BinaryWriter + Send + Sync + 'static>( - &self, - name: &CStr, - data: &'data T, - ) { + pub fn read_binary_file<T: BinaryWriter + Send + Sync>(&self, name: &CStr, data: &'data T) { self.create_file(name, data, &T::FILE_OPS) } @@ -596,11 +592,7 @@ pub fn read_callback_file<T, F>(&self, name: &CStr, data: &'data T, _f: &'static /// This function does not produce an owning handle to the file. The created /// file is removed when the [`Scope`] that this directory belongs /// to is dropped. - pub fn read_write_file<T: Writer + Reader + Send + Sync + 'static>( - &self, - name: &CStr, - data: &'data T, - ) { + pub fn read_write_file<T: Writer + Reader + Send + Sync>(&self, name: &CStr, data: &'data T) { let vtable = &<T as ReadWriteFile<_>>::FILE_OPS; self.create_file(name, data, vtable) } @@ -612,7 +604,7 @@ pub fn read_write_file<T: Writer + Reader + Send + Sync + 'static>( /// /// This function does not produce an owning handle to the file. The created file is removed /// when the [`Scope`] that this directory belongs to is dropped. - pub fn read_write_binary_file<T: BinaryWriter + BinaryReader + Send + Sync + 'static>( + pub fn read_write_binary_file<T: BinaryWriter + BinaryReader + Send + Sync>( &self, name: &CStr, data: &'data T, @@ -655,7 +647,7 @@ pub fn read_write_callback_file<T, F, W>( /// This function does not produce an owning handle to the file. The created /// file is removed when the [`Scope`] that this directory belongs /// to is dropped. - pub fn write_only_file<T: Reader + Send + Sync + 'static>(&self, name: &CStr, data: &'data T) { + pub fn write_only_file<T: Reader + Send + Sync>(&self, name: &CStr, data: &'data T) { let vtable = &<T as WriteFile<_>>::FILE_OPS; self.create_file(name, data, vtable) } @@ -666,11 +658,7 @@ pub fn write_only_file<T: Reader + Send + Sync + 'static>(&self, name: &CStr, da /// /// This function does not produce an owning handle to the file. The created file is removed /// when the [`Scope`] that this directory belongs to is dropped. - pub fn write_binary_file<T: BinaryReader + Send + Sync + 'static>( - &self, - name: &CStr, - data: &'data T, - ) { + pub fn write_binary_file<T: BinaryReader + Send + Sync>(&self, name: &CStr, data: &'data T) { self.create_file(name, data, &T::FILE_OPS) } 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 @@ pub(crate) unsafe fn dynamic_file<T>( parent.as_ptr(), core::ptr::from_ref(data) as *mut c_void, core::ptr::null(), - &**file_ops, + file_ops.fops(), ) }; @@ -127,7 +127,7 @@ pub(crate) fn file<T>( 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..5c16a3196ca2 100644 --- a/rust/kernel/debugfs/file_ops.rs +++ b/rust/kernel/debugfs/file_ops.rs @@ -20,9 +20,6 @@ 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 @@ /// 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 @@ pub(super) const fn adapt(&self) -> &FileOps<T::Inner> { } #[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 } } @@ -130,11 +127,11 @@ 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), - open: Some(writer_open::<Self>), + open: Some(writer_open::<T>), ..pin_init::zeroed() }; // SAFETY: `operations` is all stock `seq_file` implementations except for `writer_open`. @@ -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),
