rust: DebugFS Bindings

index 8cbb660e2ec218021d16e6e0144acf6f4d7cca13..655d88b8e7fe717190ccfb7b8173e84213bf8331 100644
@@ -45,6 +45,7 @@
 #include <linux/cpufreq.h>
 #include <linux/cpumask.h>
 #include <linux/cred.h>
+#include <linux/debugfs.h>
 #include <linux/device/faux.h>
 #include <linux/dma-mapping.h>
 #include <linux/errname.h>

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index 6b4774b2b1c37f4da1866e993be6230bc6715841..43f40b1baa9717ea71e4586042e9e6979491ad37 100644
@@ -66,6 +66,7 @@
 pub mod cpufreq;
 pub mod cpumask;
 pub mod cred;
+pub mod debugfs;
 pub mod device;
 pub mod device_id;
 pub mod devres;

index e390278b8b7384f1d9e2b3d7a4f5f365f6447d0f..6a89557d8cf49327d2984d15741ffb6640defd70 100644
@@ -10,7 +10,10 @@
 use crate::str::CStr;
 #[cfg(CONFIG_DEBUG_FS)]
 use crate::sync::Arc;
+use core::fmt::Display;
 
+#[cfg(CONFIG_DEBUG_FS)]
+mod display_file;
 #[cfg(CONFIG_DEBUG_FS)]
 mod entry;
 

@@ -57,6 +60,43 @@ fn create(_name: &CStr, _parent: Option<&Dir>) -> Self {
         Self()
     }
 
+    #[cfg(CONFIG_DEBUG_FS)]
+    fn create_file<T: Display + Sized>(&self, name: &CStr, data: &'static T) -> File {
+        let Some(parent) = &self.0 else {
+            return File {
+                _entry: entry::Entry::empty(),
+            };
+        };
+        // SAFETY:
+        // * `name` is a NUL-terminated C string, living across the call, by `CStr` invariant.
+        // * `parent` is a live `dentry` since we have a reference to it.
+        // * `vtable` is all stock `seq_file` implementations except for `open`.
+        //   `open`'s only requirement beyond what is provided to all open functions is that the
+        //   inode's data pointer must point to a `T` that will outlive it, which we know because
+        //   we have a static reference.
+        let ptr = unsafe {
+            bindings::debugfs_create_file_full(
+                name.as_char_ptr(),
+                0o444,
+                parent.as_ptr(),
+                data as *const _ as *mut _,
+                core::ptr::null(),
+                &<T as display_file::DisplayFile>::VTABLE,
+            )
+        };
+
+        // SAFETY: `debugfs_create_file_full` either returns an error code or a legal
+        // dentry pointer, so `Entry::new` is safe to call here.
+        let entry = unsafe { entry::Entry::new(ptr, Some(parent.clone())) };
+
+        File { _entry: entry }
+    }
+
+    #[cfg(not(CONFIG_DEBUG_FS))]
+    fn create_file<T: Display + Sized>(&self, _name: &CStr, _data: &'static T) -> File {
+        File {}
+    }
+
     /// Create a DebugFS subdirectory.
     ///
     /// Subdirectory handles cannot outlive the directory handle they were created from.

@@ -73,6 +113,22 @@ pub fn subdir(&self, name: &CStr) -> Self {
         Dir::create(name, Some(self))
     }
 
+    /// Create a file in a DebugFS directory with the provided name, and contents from invoking
+    /// [`Display::fmt`] on the provided reference.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::c_str;
+    /// # use kernel::debugfs::Dir;
+    /// let dir = Dir::new(c_str!("my_debugfs_dir"));
+    /// dir.display_file(c_str!("foo"), &200);
+    /// // "my_debugfs_dir/foo" now contains the number 200.
+    /// ```
+    pub fn display_file<T: Display + Sized>(&self, name: &CStr, data: &'static T) -> File {
+        self.create_file(name, data)
+    }
+
     /// Create a new directory in DebugFS at the root.
     ///
     /// # Examples

@@ -86,3 +142,9 @@ pub fn new(name: &CStr) -> Self {
         Dir::create(name, None)
     }
 }
+
+/// Handle to a DebugFS file.
+pub struct File {
+    #[cfg(CONFIG_DEBUG_FS)]
+    _entry: entry::Entry,
+}

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index ae0e2c4e1d58e878ebb081a71e4ac0f4a7d99b91..2baaf31c326c3071b92b5bc37552907fa1102246 100644
@@ -38,6 +38,14 @@ pub(crate) unsafe fn new(entry: *mut bindings::dentry, parent: Option<Arc<Entry>
         }
     }
 
+    /// Constructs a placeholder DebugFS [`Entry`].
+    pub(crate) fn empty() -> Self {
+        Self {
+            entry: core::ptr::null_mut(),
+            _parent: None,
+        }
+    }
+
     /// Returns the pointer representation of the DebugFS directory.
     ///
     /// # Guarantees

index 6a89557d8cf49327d2984d15741ffb6640defd70..cd83f21cf2818f406575941ebbc6c426575643e4 100644
@@ -5,12 +5,13 @@
 //!
 //! C header: [`include/linux/debugfs.h`](srctree/include/linux/debugfs.h)
 
-#[cfg(CONFIG_DEBUG_FS)]
+use crate::alloc::KBox;
 use crate::prelude::GFP_KERNEL;
 use crate::str::CStr;
 #[cfg(CONFIG_DEBUG_FS)]
 use crate::sync::Arc;
 use core::fmt::Display;
+use core::ops::Deref;
 
 #[cfg(CONFIG_DEBUG_FS)]
 mod display_file;

@@ -61,40 +62,59 @@ fn create(_name: &CStr, _parent: Option<&Dir>) -> Self {
     }
 
     #[cfg(CONFIG_DEBUG_FS)]
-    fn create_file<T: Display + Sized>(&self, name: &CStr, data: &'static T) -> File {
+    fn create_file<D: Deref<Target = T> + 'static + Send + Sync, T: Display>(
+        &self,
+        name: &CStr,
+        data: D,
+    ) -> File {
+        let mut file = File {
+            _entry: entry::Entry::empty(),
+            _data: None,
+        };
+        let Some(data) = KBox::new(data, GFP_KERNEL).ok() else {
+            return file;
+        };
+
         let Some(parent) = &self.0 else {
-            return File {
-                _entry: entry::Entry::empty(),
-            };
+            return file;
         };
+
         // SAFETY:
         // * `name` is a NUL-terminated C string, living across the call, by `CStr` invariant.
         // * `parent` is a live `dentry` since we have a reference to it.
         // * `vtable` is all stock `seq_file` implementations except for `open`.
         //   `open`'s only requirement beyond what is provided to all open functions is that the
         //   inode's data pointer must point to a `T` that will outlive it, which we know because
-        //   we have a static reference.
+        //   we have an owning `D` in the `File`, and we tear down the file during `Drop`.
         let ptr = unsafe {
             bindings::debugfs_create_file_full(
                 name.as_char_ptr(),
                 0o444,
                 parent.as_ptr(),
-                data as *const _ as *mut _,
+                data.deref() as *const _ as *mut _,
                 core::ptr::null(),
                 &<T as display_file::DisplayFile>::VTABLE,
             )
         };
 
+        file._data = Some(data);
+
         // SAFETY: `debugfs_create_file_full` either returns an error code or a legal
         // dentry pointer, so `Entry::new` is safe to call here.
-        let entry = unsafe { entry::Entry::new(ptr, Some(parent.clone())) };
+        file._entry = unsafe { entry::Entry::new(ptr, Some(parent.clone())) };
 
-        File { _entry: entry }
+        file
     }
 
     #[cfg(not(CONFIG_DEBUG_FS))]
-    fn create_file<T: Display + Sized>(&self, _name: &CStr, _data: &'static T) -> File {
-        File {}
+    fn create_file<D: Deref<Target = T> + 'static + Send + Sync, T: Display>(
+        &self,
+        _name: &CStr,
+        data: D,
+    ) -> File {
+        File {
+            _data: KBox::new(data, GFP_KERNEL).ok().map(|x| x as _),
+        }
     }
 
     /// Create a DebugFS subdirectory.

@@ -125,7 +145,11 @@ pub fn subdir(&self, name: &CStr) -> Self {
     /// dir.display_file(c_str!("foo"), &200);
     /// // "my_debugfs_dir/foo" now contains the number 200.
     /// ```
-    pub fn display_file<T: Display + Sized>(&self, name: &CStr, data: &'static T) -> File {
+    pub fn display_file<D: Deref<Target = T> + 'static + Send + Sync, T: Display>(
+        &self,
+        name: &CStr,
+        data: D,
+    ) -> File {
         self.create_file(name, data)
     }
 

@@ -147,4 +171,7 @@ pub fn new(name: &CStr) -> Self {
 pub struct File {
     #[cfg(CONFIG_DEBUG_FS)]
     _entry: entry::Entry,
+    // The data needs to be kept in a `Box` to prevent it from moving when the file does, as
+    // this might invalidate the pointer that's been passed to debugfs.
+    _data: Option<KBox<dyn Send + Sync>>,
 }

index cd83f21cf2818f406575941ebbc6c426575643e4..78544653b46d959c1520b1210170d22a0e973989 100644
@@ -10,6 +10,7 @@
 use crate::str::CStr;
 #[cfg(CONFIG_DEBUG_FS)]
 use crate::sync::Arc;
+use core::fmt;
 use core::fmt::Display;
 use core::ops::Deref;
 

@@ -153,6 +154,46 @@ pub fn display_file<D: Deref<Target = T> + 'static + Send + Sync, T: Display>(
         self.create_file(name, data)
     }
 
+    /// Create a file in a DebugFS directory with the provided name, and contents from invoking `f`
+    /// on the provided reference.
+    ///
+    /// `f` must be a function item or a non-capturing closure, or this will fail to compile.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use core::sync::atomic::{AtomicU32, Ordering};
+    /// # use kernel::c_str;
+    /// # use kernel::debugfs::Dir;
+    /// let dir = Dir::new(c_str!("foo"));
+    /// static MY_ATOMIC: AtomicU32 = AtomicU32::new(3);
+    /// let file = dir.fmt_file(c_str!("bar"), &MY_ATOMIC, &|val, f| {
+    ///   let out = val.load(Ordering::Relaxed);
+    ///   writeln!(f, "{out:#010x}")
+    /// });
+    /// MY_ATOMIC.store(10, Ordering::Relaxed);
+    /// ```
+    pub fn fmt_file<
+        D: Deref<Target = T> + 'static + Send + Sync,
+        T: Sync,
+        F: Fn(&T, &mut fmt::Formatter<'_>) -> fmt::Result + Send + Sync,
+    >(
+        &self,
+        name: &CStr,
+        data: D,
+        f: &'static F,
+    ) -> File {
+        #[cfg(CONFIG_DEBUG_FS)]
+        let data_adapted = display_file::FormatAdapter::new(data, f);
+        #[cfg(not(CONFIG_DEBUG_FS))]
+        let data_adapted = {
+            // Mark used
+            let (_, _) = (data, f);
+            &0
+        };
+        self.display_file(name, data_adapted)
+    }
+
     /// Create a new directory in DebugFS at the root.
     ///
     /// # Examples

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