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Wysocki" , Sami Tolvanen , Timur Tabi Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Matthew Maurer Content-Type: text/plain; charset="utf-8" Support creating DebugFS directories and subdirectories. Similar to the original DebugFS API, errors are hidden. By default, when a root directory handle leaves scope, it will be cleaned up. Subdirectories will by default persist until their root directory is cleaned up, but can be converted into a root directory if a scoped lifecycle is desired. Signed-off-by: Matthew Maurer --- MAINTAINERS | 1 + rust/bindings/bindings_helper.h | 1 + rust/kernel/debugfs.rs | 159 ++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 4 files changed, 162 insertions(+) diff --git a/MAINTAINERS b/MAINTAINERS index 906881b6c5cb6ff743e13b251873b89138c69a1c..a3b835e427b083a4ddd690d9e7739851f0af47ae 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -7271,6 +7271,7 @@ F: include/linux/kobj* F: include/linux/property.h F: include/linux/sysfs.h F: lib/kobj* +F: rust/kernel/debugfs.rs F: rust/kernel/device.rs F: rust/kernel/device_id.rs F: rust/kernel/devres.rs diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 8a2add69e5d66d1c2ebed9d2c950380e61c48842..787f928467faabd02a7f3cf041378fac856c4f89 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs new file mode 100644 index 0000000000000000000000000000000000000000..41ac1711e9c0e66de1a434217c363176f806f434 --- /dev/null +++ b/rust/kernel/debugfs.rs @@ -0,0 +1,159 @@ +// SPDX-License-Identifier: GPL-2.0 + +// Copyright (C) 2025 Google LLC. + +//! DebugFS Abstraction +//! +//! C header: [`include/linux/debugfs.h`](srctree/include/linux/debugfs.h) + +use crate::str::CStr; +use core::marker::PhantomData; + +/// Owning handle to a DebugFS directory. +/// +/// This directory will be cleaned up when it goes out of scope. +/// +/// # Invariants +/// +/// The wrapped pointer will always be `NULL`, an error, or an owned DebugFS `dentry`. +#[repr(transparent)] +pub struct Dir<'a, const KEEP: bool = false> { + #[cfg(CONFIG_DEBUG_FS)] + dir: *mut bindings::dentry, + // We need to be outlived by our parent, if they exist, but we don't actually need to be able + // to access the data. + _phantom: PhantomData<&'a Dir<'a, true>>, +} + +// SAFETY: [`Dir`] is just a `dentry` under the hood, which the API promises can be transferred +// between threads. +unsafe impl Send for Dir<'_, KEEP> {} + +// SAFETY: All the native functions we re-export use interior locking, and the contents of the +// struct are opaque to Rust. +unsafe impl Sync for Dir<'_, KEEP> {} + +impl<'a, const KEEP: bool> Dir<'a, KEEP> { + /// Create a new directory in DebugFS. If `parent` is [`None`], it will be created at the root. + #[cfg(CONFIG_DEBUG_FS)] + fn create(name: &CStr, parent: Option<&Dir<'a, PARENT_KEEP>>) -> Self { + let parent_ptr = match parent { + Some(parent) => parent.as_ptr(), + None => core::ptr::null_mut(), + }; + // SAFETY: + // * `name` argument points to a NUL-terminated string that lives across the call, by + // invariants of `&CStr`. + // * If `parent` is `None`, `parent` accepts null pointers to mean create at root. + // * If `parent` is `Some`, `parent` accepts live dentry debugfs pointers. + // so we can call `Self::from_ptr`. + let dir = unsafe { bindings::debugfs_create_dir(name.as_char_ptr(), parent_ptr) }; + + // SAFETY: `debugfs_create_dir` either returns an error code or a legal `dentry` pointer, + unsafe { Self::from_ptr(dir) } + } + + #[cfg(not(CONFIG_DEBUG_FS))] + fn create( + _name: &CStr, + _parent: Option<&Dir<'a, PARENT_KEEP>>, + ) -> Self { + Self() + } + + /// Constructs a new DebugFS [`Dir`] from the underlying pointer. + /// + /// # Safety + /// + /// The pointer must either be an error code, `NULL`, or represent a transfer of ownership of a + /// live DebugFS directory. + #[cfg(CONFIG_DEBUG_FS)] + unsafe fn from_ptr(dir: *mut bindings::dentry) -> Self { + Self { + dir, + _phantom: PhantomData, + } + } + + /// Returns the pointer representation of the DebugFS directory. + /// + /// # Guarantees + /// + /// Due to the type invariant, the value returned from this function will always be an error + /// code, NUL, or a live DebugFS directory. + // If this function is ever needed with `not(CONFIG_DEBUG_FS)`, hardcode it to return + // `ERR_PTR(ENODEV)`. + #[cfg(CONFIG_DEBUG_FS)] + fn as_ptr(&self) -> *mut bindings::dentry { + self.dir + } + + /// Create a DebugFS subdirectory. + /// + /// This returns a [`Dir<'_, true>`], which will not be automatically cleaned up when it + /// leaves scope. + /// To convert this to a handle governing the lifetime of the directory, use [`Dir::owning`]. + /// + /// Regardless of conversion, subdirectory handles cannot outlive the directory handle they + /// were created from. + /// + /// # Examples + /// + /// ``` + /// # use kernel::c_str; + /// # use kernel::debugfs::Dir; + /// let parent = Dir::new(c_str!("parent")); + /// let child = parent.subdir(c_str!("child")); + /// ``` + pub fn subdir<'b>(&'b self, name: &CStr) -> Dir<'b, true> { + Dir::create(name, Some(self)) + } +} + +impl<'a> Dir<'a, false> { + /// Create a new directory in DebugFS at the root. + /// + /// # Examples + /// + /// ``` + /// # use kernel::c_str; + /// # use kernel::debugfs::Dir; + /// let debugfs = Dir::new(c_str!("parent")); + /// ``` + pub fn new(name: &CStr) -> Self { + Dir::create::(name, None) + } +} + +impl<'a> Dir<'a, true> { + /// Upgrade a non-owning directory to one which will be removed on drop. + /// + /// # Examples + /// + /// ``` + /// # use kernel::c_str; + /// # use kernel::debugfs::Dir; + /// let debugfs = Dir::new(c_str!("parent")); + /// let subdir = debugfs.subdir(c_str!("child")); + /// // If subdir were dropped, the directory would not be removed. + /// let owned_subdir = subdir.owning(); + /// // If owned_subdir is dropped, "child" will be removed. + /// ``` + pub fn owning(self) -> Dir<'a, false> { + Dir { + dir: self.dir, + _phantom: self._phantom, + } + } +} + +impl Drop for Dir<'_, KEEP> { + fn drop(&mut self) { + #[cfg(CONFIG_DEBUG_FS)] + if !KEEP { + // SAFETY: `debugfs_remove` can take `NULL`, error values, and legal DebugFS dentries. + // `as_ptr` guarantees that the pointer is of this form. + unsafe { bindings::debugfs_remove(self.as_ptr()) } + } + } +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index c3762e80b314316b4b0cee3bfd9442f8f0510b91..86f6055b828d5f711578293d8916a517f2436977 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -45,6 +45,7 @@ #[doc(hidden)] pub mod build_assert; pub mod cred; +pub mod debugfs; pub mod device; pub mod device_id; pub mod devres; -- 2.49.0.906.g1f30a19c02-goog