[PATCH WIP 2/2] rust: debugfs: Extend sample to use attached data

[Matthew Maurer <mmaurer@google.com>]

Demonstrates how to attach data/handles needed for implementing DebugFS
file to a directory.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 samples/rust/rust_debugfs.rs | 110 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 106 insertions(+), 4 deletions(-)

diff --git a/samples/rust/rust_debugfs.rs b/samples/rust/rust_debugfs.rs
index 2b1119b7281fd15109b542e6853d4206c2c80afc..6da8dd2c91e8c206b2314eabb97d6d31843efeb5 100644
--- a/samples/rust/rust_debugfs.rs
+++ b/samples/rust/rust_debugfs.rs
@@ -4,10 +4,14 @@
 
 //! Sample DebugFS exporting module
 
+use core::fmt;
+use core::fmt::{Display, Formatter};
 use core::sync::atomic::{AtomicU32, Ordering};
 use kernel::c_str;
-use kernel::debugfs::Dir;
+use kernel::debugfs::{BoundDir, Dir, Values};
+use kernel::new_mutex;
 use kernel::prelude::*;
+use kernel::sync::{Arc, Mutex};
 
 module! {
     type: RustDebugFs,
@@ -20,7 +24,89 @@
 struct RustDebugFs {
     // As we only hold this for drop effect (to remove the directory) we have a leading underscore
     // to indicate to the compiler that we don't expect to use this field directly.
-    _debugfs: Dir<'static>,
+    _debugfs: Pin<KBox<Values<Backing>>>,
+}
+
+struct Composite {
+    major: u32,
+    minor: u32,
+}
+
+struct Record {
+    name: &'static CStr,
+    size: usize,
+    stride: usize,
+}
+
+struct Backing {
+    simple: u32,
+    composite: Composite,
+    custom: u32,
+    many: KVec<Record>,
+    atomic: AtomicU32,
+    locked: Arc<Mutex<u32>>,
+}
+
+impl Display for Composite {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{}.{}", self.major, self.minor)
+    }
+}
+
+impl Backing {
+    fn new() -> Result<Self> {
+        let mut many = KVec::new();
+        many.push(
+            Record {
+                name: c_str!("foo"),
+                size: 1,
+                stride: 2,
+            },
+            GFP_KERNEL,
+        )?;
+        many.push(
+            Record {
+                name: c_str!("bar"),
+                size: 3,
+                stride: 4,
+            },
+            GFP_KERNEL,
+        )?;
+        Ok(Self {
+            simple: 10,
+            composite: Composite { major: 1, minor: 2 },
+            custom: 37,
+            many,
+            atomic: AtomicU32::new(7),
+            locked: Arc::pin_init(new_mutex!(0), GFP_KERNEL)?,
+        })
+    }
+
+    fn build<'a>(&'a self, root: BoundDir<'a>) {
+        // Just prints out the number in the field
+        root.display_file(c_str!("simple"), &self.simple);
+        // Uses the custom display implementation to print major.minor
+        root.display_file(c_str!("composite"), &self.composite);
+        // Uses the custom hook print the number in 0-padded hex with some decorations.
+        root.fmt_file(c_str!("custom"), &self.custom, &|custom, f| {
+            writeln!(f, "Foo! {:#010x} Bar!", custom)
+        });
+        // Creates a directory for every record in the list, named the name of the item, with files
+        // for each attribute.
+        for record in self.many.iter() {
+            let dir = root.subdir(record.name);
+            dir.display_file(c_str!("size"), &record.size);
+            dir.display_file(c_str!("stride"), &record.stride);
+        }
+        // Access the attached atomic via `.load()`
+        root.fmt_file(c_str!("atomic"), &self.atomic, &|atomic, f| {
+            writeln!(f, "{}", atomic.load(Ordering::Relaxed))
+        });
+        // Access the attached mutex-guarded data via `.lock()`
+        root.fmt_file(c_str!("locked"), &self.locked, &|locked, f| {
+            writeln!(f, "{}", *locked.lock())
+        });
+    }
 }
 
 static EXAMPLE: AtomicU32 = AtomicU32::new(8);
@@ -28,11 +114,11 @@ struct RustDebugFs {
 impl kernel::Module for RustDebugFs {
     fn init(_this: &'static ThisModule) -> Result<Self> {
         // Create a debugfs directory in the root of the filesystem called "sample_debugfs".
-        let debugfs = Dir::new(c_str!("sample_debugfs"));
+        let root = Dir::new(c_str!("sample_debugfs"));
 
         {
             // Create a subdirectory, so "sample_debugfs/subdir" now exists.
-            let sub = debugfs.subdir(c_str!("subdir"));
+            let sub = root.subdir(c_str!("subdir"));
 
             // Create a single file in the subdirectory called "example" that will read from the
             // `EXAMPLE` atomic variable.
@@ -47,6 +133,22 @@ fn init(_this: &'static ThisModule) -> Result<Self> {
         EXAMPLE.store(10, Ordering::Relaxed);
         // Now, "sample_debugfs/subdir/example" will print "Reading atomic: 10\n" when read.
 
+        // We can also attach data scoped to our root directory
+        let backing = Backing::new()?;
+        // Grab a refcount pointing to the locked data
+        let locked = backing.locked.clone();
+        let debugfs = KBox::pin_init(Values::attach(backing, root), GFP_KERNEL)?;
+
+        // Once it's attached, we can invoke `Backing::build` to create the relevant files:
+        debugfs.as_ref().build(Backing::build);
+
+        // We can still access read-only references the contents of the attached values. If the
+        // values allow interior mutability, like atomics, this lets us still change them:
+        debugfs.as_ref().atomic.store(8, Ordering::Relaxed);
+
+        // If we attached refcounted data, we can use an external handle to access it
+        *locked.lock() = 42;
+
         // Save the root debugfs directory we created to our module object. It will be
         // automatically cleaned up when our module is unloaded because dropping the module object
         // will drop the `Dir` handle. The base directory, the subdirectory, and the file will all

-- 
2.49.0.906.g1f30a19c02-goog